Simulated Field Evaluation of Six Techniques for Controlling the Drywood Termite Incisitermes minor (Isoptera: Kalotermitidae) in Residences

Simulated Field Evaluation of Six Techniques for Controlling the

Drywood Termite Incisitermes minor (Isoptera: Kalotermitidae)

in Residences

VERNARD R. LEWIS and MICHAEL I. HAVERTY

1 Department of Environmental Sciences, Policy & Management, Division of

Insect Biology, 201 Wellman Hall, University of California,

Berkeley, CA 94720

2 Pacific Southwest Research Station, Forest Service, U.S. Department of

Agriculture, P.O. Box 245, Berkeley, CA 94701

3 This document reports the results of reseach only. Mention of

proprietary products or techniques does not constitue an

endorsement or a recommendation for its use by the University of

California or USDA.

ABSTRACT Nonchemical and chemical methods for control of drywood

termites were evaluated under simulated field conditions. Specifically, we

assessed the efficacy of four methods currently marketed as alternatives to

whole-structure fumigation for control of drywood termites: excessive heat,

excessive cold, electrocution, and microwaves. In addition, we evaluated a

reduced dosage of methyl bromide synergized with carbon dioxide, as well as

a standard fumigation treatment with sulfuryl fluoride.

Tests were conducted using Incisitermes minor (Hagen) in

artificially infested or naturally infested boards of various dimensions

used in construction. Infested boards were placed into the attic,

drywalls, or subarea of the Villa Termiti, a symmetrical building

constructed specifically for these tests. Commercial pest control

operators performed 5 of the 6 control methods; liquid nitrogen was applied

by University of California personnel. For artificially infested boards,

mortality was measured 3-d and 4-wk post-treatment. For naturally infested

boards, mortality was evaluated only 4-wk post-treatment. Efficacy

performance of all treatments was compared to 90, 95, and 99 percent levels

of mortality.

Termite mortality in artificial boards was 100 percent at 3-d and

4-wk post-treatment for both fumigant gases. Heating the whole-structure

or spot-applications using microwaves resulted in 96 and 90 percent

mortality, respectively, 3-d post-treatment. Mortality levels 4-wk

post-treatment increased to 98 percent for heating and 92 percent for

microwaves. Spot-applications of liquid nitrogen at the 30-min@1.4 kg/min

dose (highest dose tested) achieved 100 percent mortality 3-d

post-treatment. However, for the 15-min@ 0.9 kg/min and 7-min@ 0.9 kg/min

dosages, 4-wk post-treatment mortality levels were 99 percent and 87

percent, respectively. Mortality by electrocution of termites in

artificially infested boards was 44 percent 3-d post-treatment in the first

test. Four-weeks post-treatment drywood termite mortality increased to 82

percent. In a second electrocution test, using spot-application techniques

infrequently used in structures, mortality levels increased to 93 percent

3-d and 98 percent 4-wk post-treatment.

For naturally infested boards, both fumigants exceeded the 99

percent level of mortality. Nonchemical applications of heat for

whole-structure and spot-applications with microwaves resulted in 100

percent and 99 percent mortality levels for naturally infested boards.

Chemical applications of liquid nitrogen were at or near 100 percent for

naturally infested boards tested at the 30-min@1.4 kg/min and 15-min@0.9

kg/min dosages. However, mortality was significantly lower (74 percent)

for the 7-min@0.9 kg/min dose. Mortality levels from electrocution were 89

percent and 95 percent 4-wk post-treatment, respectively, in the two tests.

The distribution of termite survivors varied for some techniques by

: 1) location within the test structure and 2) galleries within test

boards. Visual signs of damage to test boards, drywall, and the Villa

Termiti were noted for some treatment techniques. This study provides

information for evaluation of the relative efficacy of nonchemical

alternatives and fumigation technology for the eradication/elimination of

drywood termite infestations in structures.

THE DAMAGE CAUSED by wood-destroying insects results in a significant

economic impact on many structures throughout the United States.

Nationwide, the cost for wood-destroying insect control and repairs of

damage approaches $5 billion per year; the outlay in California and Hawaii

alone probably exceeds $1 billion per year (Su & Scheffrahn 1990, Brier et

al. 1988). In California, a breakdown of these expenditures by insect

species reveals that subterranean termites, primarily Reticulitermes

species, and drywood termites, specifically the western drywood termite,

Incisitermes minor (Hagen), are responsible for over 95 percent of all

costs due to wood-destroying insects (Rust et al. 1988, Brier 1987).

Damage attributed to wood-boring beetles and carpenter ants amounts to

about 3 percent of the total cost (Rust et al. 1988, Brier 1987).

Subterranean termites cause problems throughout California; however, damage

by drywood termites is more common in the southern portion of the state

(Wilcox 1979). According to Wilcox (1979), over 70 percent of all

inspection reports from Los Angeles and San Diego Counties submitted to the

California Structural Pest Control Board from 1976 to 1977 indicate the

presence of damage by drywood termites. Infestations in northern

California, including the San Francisco Bay Area, the Sacramento and San

Joaquin Valleys, appear to be increasing (Lewis & Haverty, unpublished

observations). Kofoid (1934) stated that I. minor exhibited a preference

to infest rafters, roof sheathing and southern exposures of dwellings in

the northern part of its range. In southern or desert areas, infestations

are more likely to be found lower in the structure.

For many years, the standard treatment for elimination of drywood

termite infestations was fumigation with either methyl bromide or sulfuryl

fluoride. The use of fumigants is considered a "whole-structure treatment"

(for treating simultaneously all wooden members and extensive or difficult

to access infestations in structures) (Scheffrahn & Su 1994). When

properly applied, these toxic gases are effective in eliminating

infestations of drywood termites throughout the treated structure. Both

gases are highly toxic biocides that kill termites and other organisms by

disruption of biochemical pathways. Specifically, these fumigants cause

cessation of lipid catabolism and glycolysis (Meikle et al. 1963, Su &

Scheffrahn 1986). For methyl bromide, symptomology includes the darkening

of unpigmented appendages (Scheffrahn & Su 1992).

Several studies have demonstrated the effectiveness of chemical

fumigants against a variety of termite species (Bess & Ota 1960, Osbrink et

al. 1987); however, relatively little information has been presented on the

effectiveness of fumigation on an operational basis. Ebeling and Wagner

(1964) found that 26 to 37 percent of structures in Los Angeles that had

been fumigated with methyl bromide showed evidence of active drywood

termite infestations within 3 to 5 years. In the same study, they found

comparable rates of "re-infestation" for drill-and-pin applications,

ranging from 63 to 79 percent. We suggest, however, that the

"re-infestation" rate of this insecticidal spot-treatment includes a

significant proportion of termite infestations that were never eliminated.

The public is showing increased interest in nonchemical or "least

toxic" approaches to insect control. In a survey in Indiana, 87 percent of

the respondents claimed to have attempted a nonchemical method for control

of household insect pests (Bennett et al. 1983). In a similar survey, 72

percent of the respondents in Berkeley, California, said that they had

personally used nonchemical control techniques in their homes (Levenson &

Frankie 1983). A more telling statistic from this study is that 67 percent

of respondents, representing three different geographic locations of the

United States (Berkeley, California; Dallas, Texas; and New Brunswick, New

Jersey), said they were increasingly cautious about the use of pesticides.

Closely paralleling the public's interest in "Urban Environmentalism" in

California is the development and commercialization of nonchemical

alternatives directed against wood-destroying insects. The list of these

control techniques presently marketed in California for control of drywood

termites is growing and currently includes excessive heat, excessive cold,

electrocution, and microwaves (also based on temperature elevation).

Excessive cold, electrocution, and microwaves are "spot or localized"

treatment methods (treatment often restricted to a single spot within a

board or small group of boards). Whole-structure heating of homes comes

closest to conventional fumigation.

A reason for interest in the effectiveness of alternatives to

fumigation is that ownership of homes change, on average, every three years

in California (Ebeling & Forbes 1988). A usual requirement of home sales

is a guarantee that the home is free of infestations and infections of

wood-destroying organisms. Assurance of pest-free homes, without the use

or overuse of chemical pesticides, is becoming more important in closing

real estate transactions.

There has been limited published research, either in the laboratory

or in the field, on any of the alternative control methods examined in our

study. Forbes and Ebeling (1987) found that nymphs of I. minor died if

exposed to 51o C for more than 10 min. Those results form the basis for

recommendations for heat fumigation of structures. Death from exposure to

excessive heat no doubt has a complex mechanism. Hyperthermia affects

insects at the cellular level, disrupting the function of cell membranes

and stability of enzymes (Bowler 1981, Ebeling 1994).

The effects of low temperatures on termites have scarcely been

investigated. Lund (1962) determined that workers of the eastern

subterranean termite, Reticulitermes flavipes (Kollar), succumbed after

less than 5 min exposure at -9.5o C (14.9o F) to -13.0o C (8.6o F).

Temperate species such as the drywood termite Kalotermes flavicollis (F.),

the Pacific dampwood termite, Zootermopsis angusticollis (Hagen), and a

European subterranean termite, Reticulitermes lucifugus (Rossi) were able

to survive for long periods of time when held below 18o C (64o F) (Becker

1967). Feeding was minimal when the Formosan subterranean, Coptotermes

formosanus Shiraki, and R. flavipes were maintained at 5o C (41o F) and 10o

C (50o F) (Smythe & Williams 1972). At 5o C all termites of both species

died within 8 wk. All C. formosanus died when maintained at 10o C, whereas

R. flavipes survived (Smythe & Williams 1972).

In initial experiments with I. minor, Forbes and Ebeling (1986)

reported that individuals died within 5 min at temperatures between

-18.5 to -19.4o C (-1.3 to 2.9o F). Rust et al. (1995) corroborated the

experiments of Forbes and Ebeling (1986) and found that exposure of workers

(sic) and alates in wooden blocks to temperatures below -21.4o C resulted

in 100 percent mortality. This temperature is apparently below that which

causes the formation of ice crystals in the hemolymph resulting in

disruption of cell membranes and eventual death of the insect (Heinrich

1981). Both studies surmised that chilling wood below that minimum lethal

temperature will result in the elimination of all I. minor present in

timbers.

To date, there has been only one published study evaluating

efficacy of electrocution for control of drywood termites in wood. Ebeling

(1983) used the Electrogun® to treat blocks of wood artificially infested

with nymphs of I. minor. When the probe of this device was placed into a

hole near the gallery in wood containing nymphs and short bursts of

electricity were applied, sparks were seen jumping from termite to termite.

The mode of action for mortality in termites is not known. Even after

exposure to the electric shock, not all termites were killed immediately.

However, within 5 days of treatment, all termites in each "test" were dead.

Ebeling (1983) attributed delayed mortality to the destruction of

intestinal protozoans.

Similarly, when nymphs within galleries were treated by passing the

Electrogun® over the surface of the wood for one minute many termites

survived initially, although efficacy in these tests was equivocal (Ebeling

1983). As with the technique of drilling and inserting the Electrogun®

probe into the gallery, there was delayed mortality as a result of passing

the probe over the surface of the wood. After 5 days, all termites in

treated blocks were dead.

Direct treatment of termites in natural gallery systems for one

minute caused 10 percent mortality (Ebeling 1983). By placing the probe of

the Electrogun® in a "kick-out" hole, direct observation of sparking and

termite mortality demonstrated the fact that galleries in that piece of

wood were interconnected, and the device was effective in killing I. minor

nymphs.

Microwaves have been investigated as a means of destroying insects

in nuts and stored grain (Locatelli & Traversa 1989, D'Ambrosio et al.

1982, Tilton & Vardell 1982a&b, Nelson & Payne 1982, Nelson 1977, Watters

1976, Rosenberg & Bögl 1987) and for preserving textiles and museum

specimens (Hall 1981, 1988, and Philbrick 1984, Regan et al. 1980). Direct

application of microwaves to insects does not affect various life stages of

insects equally (Del Estal et al. 1986).

Microwaves can be used to heat the substrate and then subsequently

kill the infesting insects by extreme temperature (Locatelli & Traversa

1989). Microwaves can also act directly on insects within relatively dry

substrates by agitating water and/or fat molecules. Friction caused by

this agitation creates heat which likely causes death by protein

denaturation and membrane disruption (Hall 1981). Most investigators

measure the effect of the time of exposure on insects and/or substrate,

keeping the power and wavelength constant (Crocker et al. 1987). Thus far,

there have been no published reports on effects of microwaves on termites

either in the laboratory or under field conditions.

Field tests of these alternative control methods are scant. Forbes

& Ebeling (1987) reported on a demonstration of heating a mock-up house

above a critical temperature. Air from an electronically-driven blower was

passed through a gas-fired heater and delivered into the interior of this

"house." This treatment eventually raised the internal temperature of wood

in the crawl space, attic, and wall voids. Their objective was to

determine a relationship between a given room temperature and the time

required to reach lethal temperatures within structural timbers with

various cross-sectional dimensions (3.8 X 8.6, 8.9 X 28.6, or 13.9 X 28.6

cm (2 X 4, 4 X 12, or 6 X 12 inches, respectively)). For nymphs of I.

minor, 100 percent mortality was achieved when the temperature within wood

was maintained at >48o C for at least 30 min.

Forbes and Ebeling (1986) documented a method for chilling infested

structural members below the survival threshold temperature for drywood

termites. They reported that wall voids do not have to be chilled below

-80o C (-112o F) in order to reach temperatures within wooden structural

members that are lethal to drywood termites. To speed the process,

however, liquid nitrogen was used to produce temperatures as low as -180o C

(-292o F) in wall voids. These spaces remained at temperatures lethal to

termites for more than 2 hours. These authors suggested that the use of

strategically placed insulated mats decreased the amount of liquid nitrogen

required to chill the area and prevented frost formation on the walls.

There have been no published reports on the efficacy of the

Electrogun® under actual or simulated field conditions. Ebeling (1983)

reported empirical observations on the efficacy of this device after

routine commercial treatments. Softwood boards in a pile in a shed were

treated by a pest control operator who spent about 5 min treating a 3.8 X

13.9 cm (2 X 6 inches) by approximately 1 m long timber. Mortality from

this treatment was 74 percent immediately after treatment, 81.3 percent

after 26 days, and 96.3 percent after 57 days. It is important to

emphasize that this particular piece of wood was not treated in situ,

rather it "...was placed on a concrete slab and was treated with

Electrogun®, paying special attention to 'thin areas' and 'kick-out' holes."

Ebeling (1983) also examined 35 termite colonies 1-4 mo after

treatment with the Electrogun® by pest control operators. His measure of

efficacy was the appearance of new fecal pellets. Three of the 35 colonies

needed retreatment. In a survey of pest control operators who used the

Electrogun®, nearly all reported fewer call-backs than with previously

employed drill-and-treat localized chemical treatment methods (Ebeling

1983). However, Mampe (1990), citing Ebeling (1983), considered the use of

the Electrogun® to be similar to localized chemical treatments. He

described the use of the Electrogun® as follows: "the operator moves the

gun along wood members, creating an arc of high-voltage which penetrates

the wood." He does not mention penetrating the wood or galleries with the

probe of the Electrogun®. Mampe (1990) claimed that this technique "...has

met with only limited success, but may be useful for isolated infestations."

Nonchemical methods have been proposed as replacements for

structural fumigation for drywood termite control. Several of these

methods are now being applied operationally by pest control companies in

California, Florida, and Hawaii.

The economic impact of wood-destroying insects in our structures

will likely continue to increase significantly into the next century, as

will the demand for protection of wood-in-service. The reasons for this

increase are many including: 1) increased urbanization and population

growth, 2) additional environmental constraints on timber cutting and an

increase in the value of wood in North America, 3) the apparent reduced

efficacy of currently registered soil termiticides, and 4) a growing

concern of the public over the use of toxic chemicals in and around

households. Justification for development of nonchemical control

technology for drywood termites is obvious. However, the public must be

assured that alternatives to fumigation offered to them are efficacious

when properly applied.

Here we report the efficacy test results of two types of fumigation

and four methods currently marketed as alternatives to whole-structure

fumigation. We tested each method against three levels of efficacy: 90,

95, and 99 percent, after 3-d and 4-wk post-treatment. Our purpose in this

research was solely to evaluate the efficacy of each treatment, not to make

direct comparisons among treatments.

Materials and Methods

Insects. In this study, two types of infested material were used:

artificially infested and naturally infested boards. Termites placed in

artificially infested boards were extracted from naturally infested wood

(lumber, firewood, and grape prunings) containing I. minor. Infested wood

was collected from 12 cities in California: Concord, Fremont, Fresno, Los

Angeles, Novato, Oakland, Riverside, Sacramento, San Jose, San Luis Obispo,

San Rafael, and Ventura. Termites were removed from wood using Berlese

funnels or direct extraction. For the Berlese technique, cut sections of

wood were placed into the 0.5-m diameter anterior ends of funnels and

covered with friction-fitting lids containing a 100-watt light bulb. Wood

sections were left in the Berlese funnels overnight; termites fleeing from

the heat were collected at the bottom of funnels in 0.9 l glass Mason® jars

containing a damp paper towel. The method of direct extraction consisted

of using hammers and wood chisels to tap termites out of naturally infested

wood.

Termites removed by either collection technique were put into

hollowed-out birch tongue depressor rearing chambers 1.9 X 15.9 cm

long.(Bess & Ota 1960); the hollowed-out space was 1.2 X 5.0 cm long (Fig.

1). Seven of these tongue depressors were stacked onto each other and held

together with masking tape. The top and bottom of the chamber was sealed

with intact depressors; the entire unit was held together at both ends with

2-cm wide masking tape and a rubber band.

Each tongue depressor's chamber contained approximately 200

termites. Termite groups were from mixed colonies. It has been shown that

drywood termites can be mixed together with minimal mortality (Atkinson,

1994). All rearing chambers were stored in 14.3 X 10.4 X 3.4 cm (length,

width, height; lwh) clear plastic boxes with friction-fitting lids.

Plastic boxes containing the rearing chambers were held in an incubator in

a glass greenhouse for several weeks before use. Environmental conditions,

which ranged from 18 to 37 oC with relative humidities of 40 to 80 percent,

were monitored with a hygrothermograph maintained inside the incubator.

For all treatments, only healthy termites were used. Primarily, we

selected pseudergates of at least the fourth instar; however, some younger

nymphs were occasionally used. Alates and soldiers were not used in the

study.

Villa Termiti. To simulate field conditions, a mock-structure we

call the Villa Termiti, was built specifically for these tests of drywood

termite control methods. The Villa Termiti is a 6.1 X 6.1 m (37.2 m2; 20

by 20 ft or 400 ft2) building constructed of construction-grade Pacific

Douglas fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii). Walls

were built with 3.6 X 14.5 cm (2 X 6 in) studs on 30.5 cm (12 in) centers.

These studs allowed for easy installation of test boards of varying sizes.

Other dimensional sizes of wood used in construction were 2.0 X 11.6, 3.7 X

8.6, 3.8 X 23.5, 9 X 9, and 8.7 X 23.5 cm (approximately 1 X 5, 2 X 4, 2 X

10, 4 X 4, and 4 X 10 in). No pressure-treated or otherwise

chemically-treated wood was used in this building. Foundation-grade

redwood (Sequoia sempervirens (D. Don) Endl.) mudsill plates were used in

lieu of pressure-treated wood.

The Villa Termiti was designed to be symmetrical with doors and

windows on all four sides (Fig. 2). This symmetry of design allowed for

testing unbiased by construction or aspect, and it enabled internal

replication using an entire wall of wall voids. To better reflect the

different building styles used in northern versus southern California

(wooden exteriors on raised foundations versus stucco exteriors on slabs),

combination exterior walls and foundation were included in the Villa

Termiti design. The Villa Termiti contains an attic, "living space," and a

subarea (Figs. 3 & 4). The exterior of the Villa Termiti consists of

stucco walls and a shingled roof. Wooden panels with a door and two

windows are detachable and centered on each of the four walls. There are

no interior walls, insulation, or fire-blocking. However, the building

does have electrical wiring and a nonfunctional waste-water plastic (ABS)

pipe. The foundation consists of slab and a raised perimeter wall (Fig.

4C).

TheVilla Termiti was designed and constructed by licensed

contractors approved by the Operations Center, Richmond Field Station

(RFS), University of California, Berkeley. Design, construction, building

materials, and safety permits for the Villa Termiti complied with

University of California and Contra Costa County building codes and were

approved by RFS and the Fire Marshall's office, University of California,

Berkeley.

Preparation of Artificially Infested Boards. Kiln-dried, vertical

grain, and clear Douglas fir "'1 X 4s," "2 X 4s," and "4 X 6s" (1.8 X 8.7,

3.8 X 8.7, and 8.5 X 13.7 cm cross-sectional dimensions, respectively) were

cut into 61 cm lengths. On each board, 3 longitudinal cuts were made. The

first cut was a 0.6-cm thick veneer piece cut along the 3.8-cm and 8.5-cm

edge for the 2 X 4s and 4 X 6s, respectively. For 1 X 4s, a 0.3-cm thick

longitudinal cut was made along the 1.8-cm edge. The second cut was also a

0.6-cm thick veneer piece along the 8.7-cm and 13.7-cm edge for the 2 X 4s

and 4 X 6s, respectively. The 1 X 4s had a slightly thinner (0.3 cm) cut

on the 8.7-cm edges. The third longitudinal cut divided the non-veneer

8.7-cm and 13.7-cm side of each board in half (Fig. 5).

Three gallery spaces were routed into each board. The dimensions

of each routed space was 50.8 X 1.9 X 0.6 cm (lwh) for 2 X 4s and 4 X 6s.

Due to the smaller size of the 1 X 4s, the routed spaces were slightly

smaller: 50.8 X 1.6 X 0.9 cm on the 1.8-cm side and 50.8 X 1.9 X 0.3 cm on

the 8.7-cm side. Each gallery had a unique designation (Fig. 5). Gallery

1 was a centrally-routed space just under the veneer piece on the 1.8-,

3.8- or 8.5-cm side of the 1 X 4s, 2 X 4s, 4 X 6s, respectively. Gallery 2

was also a centrally-routed space just under the veneer piece on the 8.7-

or 13.7-cm sides of the boards. Gallery 3 was the routed space centrally

located in the half of the board that did not contain Gallery 2 (Fig. 5).

Since individual treatments may have varying penetration within

wood, the exposure of individual galleries to treatment could be important.

The random and asymmetrical positioning of galleries within boards allowed

us to determine how gallery orientation and wood thickness affected

treatment performance. Prior to installation, boards were held together

with two rubber bands and stored at ambient environmental conditions in the

laboratory away from excessive light. With the exception of boards used in

the untreated group, no individual board was exposed to more than one

treatment or used in more than one test.

Insertion of Insects into Boards. Seventy-five drywood termites

were placed within each board, 25 into each of the three routed galleries.

Once the termites were in place, boards were held together with a 2.5-cm

wide masking tape and individually labeled with a unique identification

number and treatment type.

Placement in the Villa Termiti. Since all treatment methods varied

in application and mode of action, two testing options, A and B, were

offered to vendors participating in this study. Option A consisted of

localized treatment of test boards only behind drywall in the Villa Termiti

wall voids. Option B consisted of a whole-structure treatment, with test

(or infested) boards positioned in the attic, the wall voids of the "living

space" and the subarea.

For Option A, 24 test boards were installed in the Villa Termiti.

The dimensional sizes of boards used were: four 1 X 4s, sixteen 2 X 4s and

four 4 X 6s. Excluding the detachable segments (the four side panels each

with one door and two windows), 24 wall voids (six in each wall) in the

drywall area of the Villa Termiti could be used (Fig. 3). The experimental

design required the use of two wall voids from each of the four sides of

the building (8 wall void spaces total). These 8 wall voids were randomly

selected from the available 24 voids, excluding the 6 wall voids which

contained electrical wiring. Three test boards were placed into each of

the randomly selected wall voids: two 2 X 4s and either one 1 X 4 or one 4

X 6. All test boards were also randomly selected.

Within each void space, there were four possible positions for

board placement, the upper and lower locations for both the right and left

studs (Fig. 3). The upper locations were positioned mid-stud and lower

locations rested on the sill plate. Three of these positions were randomly

chosen for installation of three test boards.

The orientation of galleries in the test boards within a wall void

was also randomized for each board. When viewed straight on, Gallery 1 had

two possible positions: facing the back wall of the void space or rotated

180 degrees and facing the installer. Gallery 2 also had two possible

positions, affixed to the stud or rotated 180 degrees directed away from

the stud. Because Gallery 3 was centrally located within boards, its

orientation was not greatly affected by rotation. Each board was affixed

to the studs with two 0.3-cm diameter drywall screws 5.1-cm long.

For Option B, the same methods employed in Option A were used.

Twenty-four boards were installed in wall voids behind the drywall in the

"living area." In addition, 12 boards were installed in the attic and the

subarea. Thus, a total of 48 boards were installed within the entire

structure. Treatment locations of test boards in the attic were exposed

void spaces located near the mid-line of the gable roof (Fig 3.). Two

possible sampling locations, the right or left void space, were used in

each of the four exterior walls of the attic. After randomly selecting a

void space, three test boards were installed: two 2 X 4s and either one 1 X

4 or one 4 X 6. There were three possible board locations within the void

space: the right or left stud, or against the void's exterior wall.

Individual boards were randomly assigned to a location. Two drywall

screws, described in Option A, were used to affix boards to test locations.

In the subarea, test board installation consisted of affixing

boards to the mudsill; overhanging them onto the concrete foundation or

affixing them along the mudsill plate (Fig. 3). There were three test

locations per side of the building: right and left locations on the

concrete wall and the middle of the mudsill plate.

As mentioned above, boards were randomly selected and galleries

randomly oriented prior to installation. For boards overhanging the

concrete, Gallery 1 had two possible orientations, up or rotated down 180

degrees in a vertical plane. Gallery 2, when viewed straight on, either

faced towards or was rotated 180 degrees away from the concrete wall. The

orientation of Gallery 3 remained unchanged through rotation. Boards

installed centrally on the mudsill plate were affixed midway in a

horizontal plane. The orientation for Gallery 1 when viewed straight on,

either faced the installer or was rotated 180 degrees towards the outside

wall. Gallery 2 also had two possible orientations, down towards the

mudsill or rotated 180 degrees facing upwards in a vertical plane. The

orientation of Gallery 3 remained unchanged through rotation. Two drywall

screws, aforementioned, were used to affix boards in place.

Treatment boards were installed in the Villa Termiti approximately

24 h before testing. Untreated boards were left undisturbed in a separate

building approximately 30 m from the Villa Termiti.

Placement of Naturally Infested Boards. The criteria used for

selecting naturally infested boards for the study were: 1) standard

dimensional lumber, 2) 1.8 X 18.4 cm, but not more than 8.5 X 13.7 cm in

cross-section, and 3) acoustical emission readings greater than 10 counts

per min in at least one monitored position within the board (Scheffrahn et

al. 1993). Boards were further stratified into low, medium, and high

acoustic activity. Corresponding acoustic emission readings for stratified

levels were approximately 10, 30, and >40 counts/min as registered by a

hand-held acoustic emission detector (Wood-destroying Insect Detector®,

DowElanco Indianapolis, IN). When possible, an equal number of boards

within each stratum were installed in the three areas of the Villa Termiti.

An additional consideration in the placement of boards was its ability to

fit within selected test positions in the Villa Termiti.

The actual test positions within the Villa Termiti varied between

whole-structure and localized treatment methods. For whole-structure

treatments, boards were installed in the attic, "living space," and

subarea. Three boards were placed in the attic, two in spaces between the

ceiling joists (one on the east side of the building and one on the west

side) and one in an exposed north-facing wall space (Fig. 3). In the

"living space", three boards were installed: one on the east and west

header beneath the drywall and one in a wall void (Fig. 3). For the

subarea, three boards were installed, one on each east and west 4 X 8 (8.3

X 18.4 cm) subfloor support joists and one laid on top of the north-facing

mudsill (Fig. 3).

All test boards were randomly selected and test positions randomly

assigned among boards. Localized treatments, for the most part, used the

same test positions (for exceptions, see Vendor Cooperation section). In

total, nine naturally infested boards with measurable termite activity (>10

acoustical counts/min) were used for each test.

Vendor Cooperation. The authors did not conduct any of the

applications. Licensed commercial vendors were solicited for all

applications in the Villa Termiti. All control methods tested are services

offered by firms licensed by the Structural Pest Control Board of the State

of California. Letters soliciting cooperation were written to the vendors

providing the six methods undergoing tests. Cooperation was voluntary.

We felt treatments should represent standard procedures in the

field as outlined by usage levels and vendor training manuals. Before

treatments, we requested detailed information on procedures to be used by

vendors. We also requested that all vendors use procedures that minimize

test board and structural damage. Photographs and video-recording, if

allowed by vendors, were also used to document exact procedures. All

vendor treatments were conducted separately when vendor schedules and

availability of termites allowed. Treatment effects such as temperature

and gas composition were monitored by the vendor. For a complete review of

operating procedures, safety and limitations, individual vendors should be

contacted for complete training and operating manuals. The following are

the names and normal operating procedures for firms that agreed to

participate in this efficacy study.

Fumigant gases. Sulfuryl fluoride, Vikane® fumigant gas (a

licensed product of DowElanco), was one of the two fumigants used during

the study. This fumigant is colorless, odorless and extremely harmful or

fatal to humans; therefore, it must be handled with extreme caution by

trained and certified personnel. This technique is a whole-structure

treatment. Two firms conducted the work during the testing period: Knight

Fumigation and Ultratech Division, both from San Jose, California. In

addition, the Senior Industry Specialist of DowElanco for northern

California also participated.

Normal fumigation procedure for the treatment of homes involves

sealing the house with vinyl-coated nylon tarpaulins, fans (5 amps) for

circulation of the fumigant, gas dosage calculation, infusion of the

warning agent chloropicrin, and aeration and clearing for occupant

re-entry. Dosage rate (g/m3) is dependent upon many factors: condition of

tarps, soil type, soil and air temperature, and wind conditions.

Monitoring gas concentrations is optional.

Many studies have been conducted which describe, in detail, pre-

and post-treatment preparations (Thoms & Scheffrahn 1994). For safety, all

pets, plants, and occupants must be removed from the premises during

treatment. Normal treatment time is approximately 22 h. After treatment,

the structure is aerated and cleared for re-entry according to mandated

regulatory and industry standards (Anonymous 1993). Since the entire

structure was treated, knowledge of the exact location of boards in the

Villa Termiti was not known to the vendor.

The Villa Termiti was treated three times with sulfuryl fluoride

(November 19, 1993, April 11, 1994, and September 29, 1994). In the first

fumigation 48 artificially infested boards were placed in the structure.

For the second treatment, only naturally infested boards (9 total) were

placed. For the last fumigation, both artificially and naturally infested

boards were included: 36 artificially and 9 naturally infested. All

treatment days were clear and sunny. The temperature, soil readings from

the subarea, was 10, 15.5, and 18.9o C, respectively. Wind speed was less

than 1.4 km/hr, except for the November 1993 treatment, when the wind was

recorded at 3.6 km/hr. The tarp conditions were good or excellent. Soil

type was clay and the seal condition was good. The total calculated volume

treated was 198 m3 (the actual volume of the Villa Termiti is 154 m3). The

extra treated volume included the additional tarp space for eave overhangs

and porches. The amount of sulfuryl fluoride used for each fumigation was

7.4, 2.3, and 2.5 kg. Differences in the amounts of the fumigant used

reflected the varying temperature and wind conditions for each day. A

Fumiguide® was used to calculate exact dosages required for successful

treatment. All treatments were monitored with a fumiscope; readings (ppm)

were taken in the attic, drywall, and subarea. Sulfuryl fluoride gas

levels were monitored at approximately 1 h and 22 h (just prior to tarp

removal) after gas insertion. First hour fumiscope readings for all three

treatments, 39.1 g/m3, 14.4 g/m3 and 13.5 g/m3, were at or above

recommended rates. Twenty-two hour post-fumigation fumiscope readings for

the three treatments was 14.0 g/m3, 8.9 g/m3 and 5.9 g/m3, respectively.

The second fumigant used during the study was CO2-synergized methyl

bromide, employing the MAKR® Fumigation Process. This fumigant is also

colorless, odorless, and extremely harmful or fatal to humans and must be

handled with extreme caution by trained and certified personnel.

Participating vendors included A-1 Fumigation and Farmer Pest Control

(Bellflower, California), Cal Ag (Woodland, California), and Discount

Fumigation (San Jose).

The active ingredient of this gas is methyl bromide. To enhance

the effects of the active ingredient and to minimize aeration time and

toxic gas release into the atmosphere, carbon dioxide is added as a

synergist. This synergized mixture allows a two-thirds reduction of the

normal application rate: 7.3 g/m3 reduced to 2.4 g/m3 (24 oz per 1,000 ft3

reduced to 8 oz per 1,000 ft3). The amount of carbon dioxide used is

approximately 10% of the total cubic volume of structure treated.

The Villa Termiti was fumigated three times with CO-synergized

methyl bromide (September 24, 1993, January 20, 1994, and October 13,

1994). The treatment pattern involving separate dates for treating

artificially and naturally infested boards plus one treatment combing both

types of test boards. The number of treated boards was similar to those

described above for sulfuryl fluoride. The climatic conditions for all

treatment days were sunny and clear with air temperatures of 26.7, 15.6,

and 20.0o C, respectively. Wind speed for all treatments was less than 2.4

km/hr. Trap and seal conditions were excellent for all treatments. The

total calculated volume treated was 178 m3. As with the other fumigant,

vinyl-coated nylon tarpaulins were used to enclose the entire structure.

The amount of methyl bromide used was the same for each treatment (1.4 kg)

because this fumigant has only one dosage rate irrespective of climatic

conditions. The amount of CO2 used was 31.3 kg (approximately 53.7 g/m3).

The time of exposure for all treatments was 22 h. The mixture of methyl

bromide and carbon dioxide was heated to a minimum of 70o C and then

introduced into the structure in less than 1-min through a hose. The gases

were dispersed by two 5-amp fans. A warning agent, chloropicrin, was also

added. The presence of methyl bromide and CO-2 gases was documented by

piercing the tarps and taking an internal air sample using a Draeger® tube.

Tube readings for all treatments exceeded 1,500 ppm MB and 10% for CO2

(both values are according to labeled rates). Since the entire structure

was being treated, knowledge of the exact location of boards was not known

to the vendor.

Heat. The Villa Termiti was treated with heat three times. All

test days (October 29, 1993, January 17, 1994, and December 1, 1994) were

sunny and clear. The coldest initial temperatures in the Villa Termiti

prior to heating for each treatment date were 15o, 12.2o, and 8.9o C: all

were found in the same attic beam. J. H. Steffenson Termite Control

(Campbell, California) in conjunction with Isothermics/Thermal Pest

Eradication® (TPE) (Orange, California) applied the heat treatments. Two

vinyl-coated nylon tarpaulins were needed to enclose the structure prior to

treatment. The tarpaulins had several tears to allow air movement through

the structure (hot air was continuously circulated through the Villa

Termiti). Thermocouples were placed throughout the structure to record

temperature changes (Fig. 6). The number of thermocouples used varied with

each test: 6 thermocouples were used during the first test, 10 for the

second, and 11 for the third. Four convection heaters (each 400,000 BTUs),

through flexible Mylar® ducts.

The objective of heat treatment is to have the temperature of the

coolest thermocouple, normally in a large wooden member or mudsill in the

subarea, reach at least 48.9o C and remains at that temperature for 30 min.

Total treatment time is typically about 6 h for a two-bedroom home (Ebeling

1994). Two 4.3-amp fans were positioned in the structure (subarea and

drywall areas) to insure uniform heat distribution. During normal

operations, air temperatures within living spaces are not to exceed 65.6o C

to minimize any damage to the treated structure or its contents. The Villa

Termiti was vacated during treatment; however, entry into the building was

possible, though uncomfortable, even at these elevated temperatures. Since

it as a whole-structure treatment, knowledge of the exact location of test

boards was not known to the vendor.

Liquid Nitrogen. There was no vendor cooperation for this

treatment method. All liquid nitrogen treatments in the Villa Termiti were

conducted by research personnel from the University of California, Berkeley

and Riverside. Since this is a spot-treatment technique, knowledge of the

location of test boards in the Villa Termiti was made known to personnel

conducting the treatments. Optimal performance of liquid nitrogen requires

an enclosed void space for containment of the liquid and vapor. A 1.3-cm

diameter hole was drilled through the drywall near the top plate of the

void space being treated. Liquid nitrogen (Altair Gases & Equipment, Inc.,

Oakland, California) was then injected from 160 l dewars into the wall

cavity through a 1.2-m flexible woven stainless steel hose. The

temperature inside the dewar may be lower than -195.8o C.

In our tests we attempted to have a constant amount of liquid

nitrogen delivered to each wall void. We calibrated the time it took to

deliver a standard dose. In the first test, we delivered liquid nitrogen

at approximately 30 min @ 1.4 kg/min into each 14.5 X 30.5 X 244 cm wall

void (n = 13 separate wall voids). In the second test, we delivered

slightly less than one-half and the third test one-fourth the rate applied

during the first test (0.9 kg/min for either 15 min or 7 min). A digital

scale (Pennsylvania 66000, 1.2 m2 platform, 2,268 kg capacity) was used

during the first test to determine pre- and post-application weights of

liquid nitrogen. A full-capacity beam scale (Howe Richardson Mechano-Weigh

54 XL) was used to record changes in liquid nitrogen weights for the two

additional tests.

Twelve thin-wire thermocouples were used to monitor temperature

changes within studs and test boards in wall voids of the Villa Termiti.

The ends of the wires were inserted into a scanning thermocouple

thermometer (Cole-Parmer model #92800-00) that was connected to a serial

printer via an RS-232 output. Temperature readings were taken every minute

from 12 different locations in "2 X 6-in" (3.6 X 14.5 cm) studs and test

boards for each corner of the building (6 possible void spaces per corner)

(Fig. 7). Control should be reached when the temperature falls below

-28.9o C for at least 5 min (Tallon 1992); the temperature inside the dewar

may be less than -184.4o C.. Insulation blankets were used to help

maintain the frigid temperatures for the last two tests. For safety, the

oxygen content of the living space was monitored, protective clothing was

worn, and the "buddy system" was used.

Electrocution. Etex, Ltd., Las Vegas, Nevada, manufacturer and

distributor of the Electrogun®, supplied all equipment and personnel for

the treatment. The equipment used is commercially marketed as the

Electrogun®, a device that kills drywood termites by emitting high

frequency electricity (100 kHz), high voltage (90,000), but low current (<1

amp). Whole-house and spot-treatment options are offered by vendors. For

exposed 2 X 4s and smaller pieces of wood, the probe end of the device was

placed against the wood surface. For larger pieces of wood and wood

concealed behind drywall, a "drill-and-pin" method was used.

For the "drill-and-pin" method, small (1.6 mm diameter) holes were

drilled through the drywall and into the wood. Approximately 15.2-cm long

straight copper wires were inserted into the holes and into the termite

galleries. Several consecutive drillings per hole were used to insure that

the electrical current was delivered at various depths within the boards.

For tests in the Villa Termiti, knowledge of the location of test boards

behind drywall was revealed to the vendor.

For optimal performance, thorough coverage of infested wood is

crucial. This method may also be used with other treatments such as

chemical liquids or dusts that can be applied into galleries or onto the

surface of infested timbers. The training information and equipment manual

do not recommend using this method in close proximity to metals, concrete,

excessive moisture, laminated finishes or electronic items. Use in

inaccessible areas is also not recommended (nor is it practical). This

treatment method is available only to licensed professional operators who

lease the equipment and undergo an extensive mandatory training program.

When properly used, this device is reportedly safe for operator and

building occupants; no potentially harmful radiation is emitted.

An additional and different test in the Villa Termiti was requested

by the Etex Corporation because they felt the conditions of the first test

produced results biased against the Electrogun®. They were concerned about

proximity of test boards to metal (wire-mesh in stucco and metal support

bars in detachable walls) and to concrete in the foundation of the subarea.

They felt the performance of the Electrogun® would be improved if tested

against infested boards in locations without interfering metal or concrete.

For the second electrocution test, 18 artificially infested boards

were installed in locations away from sources of metal and concrete. Six

boards each were installed in the attic, "living space," and subarea. In

the attic, boards were randomly placed on one of two 2.7-m long rafters

adjacent to the vertical wall for each side of the building; thus, there

was a total of 8 possible sampling locations (Fig. 3). In the "living

space", each board was installed in a wall void (2.0 X 0.2 X 0.1 m) in the

detachable walls only. There were 16 total wall voids possible for

selection; four for each side of the building (Fig. 3). Except for the

metal window frames and nails, the detachable walls do not contain

significant amounts of metal. For the subarea, floor joists were used for

board installation; no boards were placed on or near the sill plates or

foundation. Six joists were randomly chosen from a possible total of 46.

The preparation, fastening, randomization, and orientation of test boards

were similar to the earlier test. The vendor was asked to treat the boards

as before. Fifteen controls, or untreated boards, were kept in the same

nearby building (see above).

Naturally infested boards were similarly installed. In total, nine

naturally infested boards were installed in the Villa Termiti for this

second test: three boards each in the attic, living space, and subarea. In

the attic, two ceiling bays and one rafter were used. In the living space,

three void spaces in the detachable walls (different from those containing

artificial boards) were used. In the subarea, three floor joists

(different from those containing artificial boards) were used. The

preparation, fastening, randomization, and orientation of boards were also

similar to the earlier test.

Microwaves. The Termite Inspector (Mission Hills, California)

supplied the equipment and personnel to conduct all tests in the Villa

Termiti. Treatment procedures included treating infested wood with a

700-watt (more powerful devices are available from other vendors). The 2.4

GHz frequency oscillation causes vibration of water molecules within

termites, which produces lethal temperatures above 48.9o C. This

spot-application method treats a section of wood approximately 10.2 X 30.5

cm when operating. For safety, the device is operated remotely, and all

persons are kept a minimum of 9.1 m from the apparatus while it is

operating. Protective blankets are used, if necessary, for added safety.

Under field conditions, the vendor uses visual, acoustical, or fiber

optical devices to locate infestations. For tests in the Villa Termiti,

the location of test boards was disclosed to the vendor. Once boards were

identified for treatment, the microwave instrument was positioned over the

treatment spot, technicians left the room, and the device was operated by

remote. Treatment time was approximately 8 min per spot (10.2 X 30.5 cm;

311 cm2). A hand-held microwave detection device (Model HI-1801, Holaday

Industries, Inc.) was used to selectively monitor emissions from the

opposite side of the wall during treatment.

Assessment of Treatment Efficacy. The day following treatment, all

artificially infested boards (24 to 48 total) were removed from the Villa

Termiti and stored in the laboratory until they were opened for 3-d

post-treatment assessment of mortality. Live and dead termites were

counted and removed from each gallery in every board. Live termites from

each gallery were placed in a separate tongue depressor holding chamber

(Fig. 1). each individual holding chamber was stored in a clear, 15.5-cm

diameter plastic container with a lid and placed in an incubator stored in

a glass greenhouse. The percent mortality of these termites was determined

at 4-wk post-treatment. Percent mortality was defined to include both

carcasses and those missing. Since termites are cannibalistic and eat

their dead and injured, we used this measure of mortality. Termites

smashed by handling and recording miscounts (gained numbers of termites)

were excluded from the analysis. Dead insects were stored in clear 23 X 23

X 20 mm plastic boxes with lids for future verification. Untreated boards

("controls") containing 25 termites in each of three galleries were

assessed in the same manner as treated boards.

After each test, the nine naturally infested boards were removed

from the Villa Termiti and stored in the same glass greenhouse as the

artificial boards. Boards were acoustically monitored at 1-, 2-, and 4-wk

post-treatment (these data will be reported separately). At 4-wk

post-treatment, the boards were cut into small lengths (approximately

10-cm) and carefully dissected. The sections of board were split with a

hammer and wood chisel until it was clear there were no more termites in

every gallery and chamber in the board. Live and dead termites were

counted and sorted by caste (alate, soldier, and nymph/pseudergate) and

percent mortality was calculated based on these data for each board. All

insects, dead and alive, were stored in labeled, clear 23 X 23 X 20 mm

plastic boxes with lids for future verification.

For each artificially infested board, the percent mortality was

calculated by combining the counts of live and dead termites for all three

galleries. Thus, the experimental unit for this portion of the test was

the board. In addition, separate records were kept for each gallery so

that we could explain anomalies in mortality as a function of the unique

placement of a particular gallery within the wall voids or near the

foundation. Occasionally the termites burrowed through the sawed portion

of the board and moved from one gallery to another. An additional

complication was that as a result of the "drill-and-pin" method of applying

the Electrogun®, holes were left in the boards, allowing termites to

escape. If the total number of termites remaining in an individual

artificially infested board was less than 48, the data for that particular

board was discarded for analysis. Galleries not containing any termites

were also discarded from further analysis. Since we had little control

over the number of termites in a naturally infested board, we calculated

percent mortality using all of the live and dead termites removed from the

board.

For each treatment, the weighted mean response ( ) and the standard

error of the weighted mean ( ) for artificially infested and naturally

infested boards were determined using the following formulae:

where

= the mean mortality for a board in the th location in the building and

for the th size board.

= the standard error associated with a particular mortality ( ).

= the proportion of lumber of dimension placed in test within location .

= location in the building: (1) attic, (2) living area, and (3) subarea.

= dimension of lumber: (1) 1 X 4 or 1 X 8; (2) 2 X 4; and (3) 4 X 4, 4 X

6, 4 X 8, or 4 X 12.

The relative proportion of wood, 1 X 4s, 2 X 4s, and 4 X 6s, for

each location within the Villa Termiti was calculated using the following

formula and was equal to one.

In calculating a weighted percent mortality for a building, we

assumed equal rates of infestation for all three areas of a home. For a

given locality this may not be true. For example in Riverside and Palm

Springs, California, or Phoenix, Arizona, infestations of drywood termites

would likely be restricted to the subarea or window and door frames.

Infestations are not common in the attic area in these desert locations.

In contrast, drywood termite infestations in coastal California are common

in the attic, walls, and even in the subarea.

We assumed no density dependence in efficacy of any of the

treatments. For the artificially infested boards, this is not a problem

since we kept density constant. For the naturally infested boards we were

not able to regulate density of drywood termite populations. We did

estimate relative densities of the populations in each board before each

test using acoustic emission counts (Lewis et al. 1991). We then

stratified the boards used for a particular test into low, medium, and high

populations. We positioned these boards, stratified on the basis of

apparent termite density, throughout the Villa Termiti by placing an equal

number of each category in each location/level.

Treatments were not statistically compared to one another. The

efficacy of each treatment was tested against a set of standards. Our null

hypothesis was that each treatment is ineffective, i.e. the treatment

resulted in mortality less than or equal to 90 percent (Ho: p < 0.90). The

alternative hypothesis was that each treatment resulted in a mortality

greater than 90, 95 or 99 percent (Ha: p > 0.90). The equation used to

test the significance of the hypothesis is:

where

m = level of mortality desired or required.

All statistical tests of efficacy were determined by a one-tailed

t-test to determine whether the mean response exceeded the standard level

of mortality (Steel and Torrie 1960). Statistical significance was tested

at the a = 0.05 level with degrees of freedom equal to the number of boards

minus 1. The number of boards, or replicates, varied among treatment

methods. For spot-treatments, a replicate was an individual board. For

whole-structure treatments, one application of the method to the entire

structure would ideally be considered a replicate. However, for this

study, each board for all treatment methods was considered a replicate.

Summary statistics for mortality levels among location, board

dimension, and gallery designation were derived with the MEAN procedure

(PROC MEAN, SAS Institute 1994). Means for termite mortality levels among

Villa Termiti locations, board dimension, and gallery designation were

analyzed for significant differences using the Ryan-Einot-Gabriel-Welsch Q

multiple range test (PROC GLM, SAS Institute 1994). Untreated board

replicates for each treatment method were pooled and mortality levels

analyzed by board dimensional size and gallery designation using

Ryan-Einot-Gabriel-Welsch Q multiple range test (PROC GLM, SAS Institute

1994). All artificially infested boards were visually inspected after

treatment for signs of damage: drilled holes and burn marks. Differences

in the number of damaged boards among treatment methods were analyzed using

the Ryan-Einot-Gabriel-Welsch Q multiple range test (PROC GLM, SAS

Institute 1994). Differences in treatment time and number of drilled holes

between the two electrocution tests were analyzed using paired t-tests

(PROC TTEST, SAS Institute 1994).

Results and Discussion

Fumigant Gases

Sulfuryl fluoride. Termite mortality for all treated

artificially infested boards was 100% (Table 1). The overall mean

mortality value for the entire structure was significantly greater than the

90, 95, and 99% levels of acceptance (Table 2). Therefore, the efficacy of

this treatment significantly exceeds the 99% mortality level. These data

agree with previously reported laboratory studies in sulfuryl fluoride

efficacy (Su & Scheffrahn 1986, Osbrink et al. 1987, Thoms & Scheffrahn

1994). Control mortality at 3-d was low (< 5%), suggesting high

survivorship in test boards prior to treatment. However, mortality after

4-wk increased more than 5-fold, suggesting increased natural and handling

mortality post-treatment. Differences in mortality among board dimensions

for controls were nonsignificant (F test, P > 0.05) at 3-d and 4-wk

post-treatment.

The overall mean mortality value for naturally infested boards was

also significantly greater than the 99% (Tables 2 & 3). Only a solitary

soldier survived. Although a single survivor among thousands is

insignificant, this finding is scientifically curious. Lethal sulfuryl

fluoride dosages for soldier castes for a number of termite species have

been previously reported (Osbrink et al. 1987). However, values for I.

minor were not included. Perhaps future studies may include the

determination of the lethal dose for the soldier caste for I. minor.

Except for warping, no visual signs of damage were noted for test

boards treated with sulfuryl fluoride (Table 4). However, all test boards

experienced some signs of wood distortion, especially the thin veneer

pieces. Desorption and residual studies for sulfuryl fluoride report its

safety for many household commodities if properly used and aerated after

treatment (Kenaga 1957, Osbrink et al. 1988, Scheffrahn et al. 1987, 1989a,

1989b).

CO2-synergized methyl bromide. Termite mortality for all

artificially infested boards was 100% (Table 5). The overall mean

mortality value was significantly greater than the 99% level of efficacy

(Table 2). Control board mortality at 3-d was moderate and ranged from 8.0

to 16.2% (Table 5). Natural and handling mortalities for controls

increased at least 2-fold 4-wk post-treatment. The differences in

mortality among board dimension for control boards for 3-d and 4-wk

post-treatment was nonsignificant (P > 0.05). The mortality level for

naturally infested boards was also significantly above the 99% level

(Tables 2 & 6). However, 30 survivors were found in one 2 by 4 in the

subarea. None of the survivors were reproductives. Therefore, we conclude

that this synergized, reduced application rate of methyl bromide

significantly exceeds the 99% mortality level.

Dose mortality curves for drywood termites (I. synderi) using

CO2-synergized methyl bromide have been reported (Scheffrahn et al. 1995).

Scheffrahn & Su (1992) have also reported that label rates for methyl

bromide were excessive by as much as 4-fold. Both papers support claims of

high levels of efficacy for reduced methyl bromide dosages. Results from

this study support these earlier findings and suggest that care must be

taken in calculating dosage, as well as placement and number of fans when

using reduced methyl bromide methods, especially in subareas.

Visual signs of damage to test boards was minimal for this

treatment and restricted to warping of some 2 by 4 and 4 by 6 test boards

(Table 4). However, other studies have shown that some household foods, if

not enclosed in protective nylon bags, can serve as sorptive matrices for

this fumigant (Scheffrahn et al. 1990, 1992). (Rudi, can your "Indoor

airborne residues of methyl bromide and sulfuryl fluoride following

aeration of fumigated houses" paper be cited?). Methyl bromide has also

been reported to be an ozone depletor (Cicerone 1987). Registration of

methyl bromide is scheduled for phase-out by the U. S. Environmental

Protection Agency (EPA) by the end of the decade (Kramer 1992).

Nonchemical Methods

Excessive heat. Termite mortality in artificially infested boards

was 100 percent except in the subarea (Table 7). Mortality levels were

significantly greater than the 90 percent efficacy levels after 3-d and

significantly greater than the 90 and 95 percent levels after 4-wk (Table

2). The subarea was the only location that mortality levels did not reach

100 percent. Mortality values for the subarea at 3-d and 4-wk

post-treatment was 85.8 and 91.1 percent. Both values were significantly

different from mortality values for the attic and "living space" (F = 17.6;

df = 2, 80; P < 0.0001; F = 11.4; df = 2, 83; P < 0.0001). It was

initially thought that the early removal of test boards during the first

test, immediately after treatment to protect termites from predation by

Argentine ants, Linepithema humile (formerly Iridomyremex humilus), may

have interfered with test results. However, results from the second test,

when boards were not removed early, revealed a similar pattern of

survivorship in the subarea.

Analysis of data for the subarea revealed an uneven distribution of

mortality for artificially infested test boards. The size of the

artificially infested boards did not have a significant impact on mortality

levels achieved at 3-d or 4-wk post-treatment (P > 0.05)(Table 7).

However, the data for individual galleries within boards revealed that

survivorship only occurred in Gallery 2; locations affixed against the

foundation wall (Fig. 4). At 3-d post-treatment the mortality value for

Gallery 2 (78.2 percent) was significantly lower than Gallery 1 (94.5

percent) and Gallery 3 (92.2 percent)(F = 7.1; df = 2, 208; P < 0.0011).

Similarly at 4-wk post-treatment the mortality value for Gallery 2 (80.7

percent) was significantly lower than Gallery 1 (95.3 percent) and Gallery

3 (92.8 percent) (F = 6.4; df = 2, 208; P < 0.002). Data from

thermocouples revealed that all probes reached the 50o C lethal temperature

for at least 1 h (Table 8); however there were still survivors. It is not

known how much more additional time would have been required to achieve 100

percent mortality for test boards in the subarea. Perhaps future studies

can focus more on thermocouple position and number in subareas and sill

plates on slabs.

Termite mortality for controls was initially high for 1 by 4s

(Table 7). Four-week control mortality values among boards, albeit were

large and ranged from 24.2 percent in 2 by 4s to 43.5 in 1 by 4s, were not

significant (P > 0.05). These results, probably due to overheating of some

boards while in transit to the laboratory from the Villa Termiti, suggest

termite robustness was less for the heat treatment than for other methods

tested.

Mortality results for naturally infested boards was 100 percent for

all test locations in the Villa Termiti (Table 9). Mean mortality was

statistically significant at the 90, 95, and 99 percent levels of efficacy

(Table 2). From the results with artificially infested and naturally

infested boards we conclude that excessive heat, applied as described,

results in a mortality level that significantly exceeds 95 percent and

perhaps as high as 99 percent.

There were a few visual signs of damage, minor warping for some 2

by 4 and 4 by 6 test boards (Table 4). Other changes noted in the Villa

Termiti included sticking of doors (reversible), fluorescent lights

going-out (reversible) and warping of a non-functional ABS plastic

waste-water pipe (non-reversible). However, under normal field conditions,

a low volume of cold running water is left on to prevent the warping of

plastic pipes. Minor structural damage from heat treatment, as well as

pre-treatment preparations to minimize damage to household items, have been

previously reported (Forbes & Ebeling 1987, Ebeling 1994).

Excessive Cold. Our assessment of the effectiveness of

spot-treatments with liquid nitrogen was mixed and highly influenced by

dosage and thermocouple placement. At the highest dosage tested, 30 min

@1.2 kg/min, both 3-d and 4-wk mortality of drywood termites in

artificially infested boards was 100 percent (Table 10). At this dosage,

mortality was significant for all efficacy levels tested (Table 2).

Similarly, the 3-d and 4-wk mortality levels for the 15-min @ 0.9 kg/min

dosage was statistically significant at the 90 and 95 percent efficacy

levels (Tables 2 and 10). However, for the lowest dosage of 7-min @ 0.9

kg/min, the 3-d mortality value, 84.4 percent, was much less efficacious

(Table 10); this value was not statistically different at the 90 percent

level (Table 2). The 4-wk mortality value, 87 percent, although slightly

higher, was still not statistically significant at the 90 percent level of

efficacy (Tables 2 and 10). Control mortality levels at 3-d post-treatment

were less than 5 percent, suggesting termites were robust prior to

treatments. However, 4-wk mortality increased approximately 5-fold for

controls indicating considerable natural and handling mortality. There

were no significant difference in mortality levels among board dimensional

size or gallery designation for control boards (P > 0.05). Rust et al.

(1995) contain data tables that report the minimum dosage rate required to

achieve 100 percent control with liquid nitrogen was at least 21 min @0.9

kg/min in an uninsulated 2.4 by 2.0 m (8-ft by 6.6-ft) artificial wall used

in their tests. Their results are clearly in agreement with those reported

in Table 10. Lower dosage rates and application times are not likely to

achieve the minimal lethal temperature.

Lumber dimensions appear to affect termite mortality, at least for

the two lower dosages of liquid nitrogen tested. The 4 by 6 boards

suffered less mortality than the other board dimensional sizes when treated

with the 15-min and 7-min @ 0.9 kg/min dosages (Table 10). The termites in

the 1 by 4 boards always experienced the greatest level of mortality in

these two lower dosages. However these differences were not statistically

significant (P > 0.05). Wood is a poor thermal conductor (Forest Products

Laboratory 1987). Results from the current suggest that wood, if

relatively sound, may provide termites with insulation and protection from

the lethal effects of excessive cold.

Considerable variance in temperature was recorded in wall voids for

all liquid nitrogen dosages tested (Tables 11, 12, and 13). Treated boards

containing live termites for the 15-min and 7-min @ 0.9 kg/min dosage rates

appeared to be associated with thermocouples failing to achieve lethal

temperatures (Tables 12 and 13). However, for the 7-min @ 0.9 kg/min dose,

three artificially infested boards (two 2 by 4s and one 4 by 6) contained

termite survivors. These boards were located in treated wall voids

containing thermocouples that reported minimum lethal temperatures (S3 and

W2, Table 13). These results suggest that higher dosage rates and

thermocouple placement are critical for achieving high levels of efficacy.

Naturally infested boards revealed a similar pattern to that of

artificial boards; decreasing levels of mortality with decreasing dosage

rates (Table 14). For the 30-min @1.4 kg/min rate, termite mortality was

100 percent. The overall mean mortality value was significantly greater

than 90, 95 and 99 percent (Table 2). Similarly, at the 15-min @ 0.9

kg/min dosage, mortality was significantly greater than all efficacy levels

tested (Table 2). However, the 7-min @ 0.9 kg/min dosage rate achieved an

overall mortality level of 74.3 percent (Table 14). This mortality rate

was not significantly greater than the 90 percent level of efficacy (Table

2) and live alates were found among the survivors for the 15-min and 7-min

@ 0.9 kg/min rates. Similar to the results with artificially infested

boards, the existence of termite survivors was associated with failure of

achieving minimum lethal temperatures. Three termite survivors were found

in a naturally infested 2 by 4 at the 15-min @ 0.9 kg/min dose rate albeit

lethal minimum temperatures were achieved for top and bottom positioned

thermocouples (N3, Table 12).

Because we were not able to obtain information on application rates

from a vendor who applies liquid nitrogen, we had to assess different

dosage rates to determine a minimum application rate that was efficacious.

The wall voids in the Villa Termiti are approximately 14 by 28 by 224 cm

with an internal volume of 87,808 cm2 (87.8 l). Clearly, the 7-min @ 0.9

kg/min (63 kg of liquid nitrogen) dosage is not an effective treatment for

any reasonable level of mortality that would be desired. We feel that the

15-min @ 0.9 kg/min (13.5 kg of liquid nitrogen) application rate is the

absolute minimum to achieve a reasonable level of mortality (> 95 percent).

This application rate places liquid nitrogen into the wall void at a

concentration of 154 g of liquid nitrogen/liter. Application rates

exceeding this level are more likely to provide mortality levels in excess

of 99 percent.

Visual damage to boards from liquid nitrogen treatments was minimal

(Table 4). Frost formation during treatment can be considerable and may

cause damage to some wall coverings. However, the possibility exists for

microscopic wood damage that may result in structural failure during stress

(e.g., earthquakes). Future studies are needed to explore microscopic

damage and the possible loss of wood strength for varying dosage levels of

liquid nitrogen. With this treatment, repair of drilled insertion holes is

required.

Electrocution. Efficacy of electrocution treatments from the first

test were below the minimum level of acceptance for artificially infested

boards. Drywood termite mortality levels at 3-d post-treatment in

artificially infested boards were well below 50 percent in the attic and

subarea (Table 15). Only in the drywall area did mortality levels reach 50

percent or higher. The overall mortality value for the entire structure

was 43.8 percent 3-d post-treatment (Table 2). Four weeks post-treatment,

mortality levels increased to 81.2 percent. However, this efficacy value

was still significantly below the minimum 90 percent level of acceptance

(Table 2). For treated locations within the Villa Termiti, the attic,

drywall, and subarea locations had mortality values of 25.5, 54.2, and 46.3

respectively. At 3-d post-treatment, mortality values for the drywall and

subarea locations were significantly greater than the attic (F = 9.6; df =

2, 142; P < 0.0001). The were no significant difference in mortality

values among board dimensional sizes (P > 0.05). However, gallery

differences in percent mortality within boards were considerable; 61.8

percent for gallery 1, 26. 8 percent for gallery 2, and 46.0 percent for

gallery 3. All gallery mortality levels were significantly different from

each other (F = 13.9; df = 2 142; P < 0.0001). Similarly, 4-wk

post-treatment, mortality values among treated areas within the Villa

Termiti and gallery locations within boards were still significantly

different (F = 31.3; df = 3, 187; P < 0.0001; F = 13.6; df = 2, 187; P <

0.0001). Variable results while using electrocution ranging from 3 - 100

percent mortality for boards artificially infested with drywood termites

have previously been reported (Ebeling 1983). Mortality results for

naturally infested boards in the first test resulted in a similar pattern

to artificially infested boards of low mortality (Table 16); 8 of 9 boards

contained termite survivors while 2 of these 8 boards had several hundred

survivors. The overall mortality level, 88.6 percent at 4-wk

post-treatment, did not significantly exceed the 90 percent level of

efficacy (Table 2).

There are several reasons that may explain the poor performance of

electrocution during the first test. First, penetration of electric

current into wood is limited. Ebeling (1983) reported that the surface

application of electricity is restricted to only 1.3 cm deep into wood.

However, for the current study, the size of boards containing termites was

not a factor; there were no significant differences in mortality among

board dimensional sizes (P > 0.05)). The depth of galleries containing

termites also appeared to be unrelated to termite mortality since the

deepest gallery, Gallery 3, had a higher mortality percentage than Gallery

2, the shallowest. In fact, the drywall locations, sites on non-exposed

wood had significantly higher levels of mortality than the exposed test

boards in the attic (3-d and 4-wk results, Table 15).

A second possible limiting factor for electrocution treatments is

delayed mortality (Ebeling 1983). However, the increased mortality

observed at 4-wk post-treatment, as high as 4-fold, was probably not due to

the effects of electrocution. Levels of mortality in the controls were

also higher, as high as 60-fold, and suggest that increased mortality seen

in boards treated by electrocution at 4-wk post-treatment was due to

natural mortality and handling (Table 15).

The results from the first test of both artificially and naturally

infested boards were challenged by the vendor conducting the electrocution

techniques as being bias against the electrocution techniques because

standard operating procedures were not strictly adhered to. The reasons

given for this poor performance (the presence of test boards next to stucco

walls, wire supports in stucco, and concrete in the subarea) suggest that

electric current was drawn away from the treated areas and thus away from

the targeted termites. A second test, smaller in scope and with test

boards positioned in more favorable, "wooden" locations was conducted to

remedy these concerns.

The results from a second test of electrocution of boards in

locations away from metal and concrete were much improved. Three-day

assessment of artificially infested boards resulted in mortality levels

that were not significantly above the 90 percent level (Tables 2, 16).

Mortality levels at 4-wk post-treatment (98.5 percent) significantly

exceeded the 90 and 95 percent levels of efficacy (Table 2).

Mortality of naturally infested boards was also higher than in the

first test (Table 16). Only 5 boards contained survivors, as compared to 8

in the first test. However, one board contained over 100 survivors. The

mortality level in naturally infested boards for the entire structure was

95.1 percent and significantly exceeded only the 90 percent level of

efficacy (Table 2).

The improved performance of electrocution in the second test

requires some discussion. Ebeling (1983) claimed the mortality effects of

electrocution are heightened when test boards were placed on a metal table.

The results of the current study suggest an opposite interpretation: metal

impedes the effects of electrocution. However, this finding is confounded

by 2 factors: significantly more time was spent treating test boards in the

second test as opposed to the first (7.5 min vs. 20.0 min, t = 5.9; df = 1,

38; p < 0.0001) and significantly more holes were drilled per board during

the second test (6.5 versus 12.0, t = 3.3; df = 1, 61; p < 0.0015). Range

in treatment time for each board varied from 5 min to 1.75 h. Since most

of the test boards were treated with the drill-and-pin technique (59 of 66

for artificially infested boards and 14 of 18 naturally infested boards),

statements cannot be made about passing the probe end emitting electricity

over boards when treating. Future studies are needed to determine the

effects of treatment exposure time and insertion of metal pins upon termite

mortality.

We conclude that the efficacy of this treatment appears to be

technique-driven. Clearly, electrocution causes mortality in termites.

However, to achieve reasonable levels of mortality the operator should use

the drill-and-pin technique and spend as much time as possible treating an

infested area. This control method, more than any of the other tests in

this study, requires precise information as to the extent and location of

the drywood termite infestation. Without accurate delimiting of the

infestation, efficacy will surely drop to unacceptable levels.

Damage to test boards using electrocution was considerable (Table

4). Eighty percent (53 of 66) of artificially infested boards and

seventy-eight percent (14 of 18) of naturally infested boards, revealed

visual signs of damage. Most signs of damage were drill holes from

administration of the drill-and-pin technique. However, 29 boards revealed

minor burn marks within test boards. Ebeling (1983) reported wood is a

poor insulator and could be carbonized or destroyed as a current seeks a

path to ground during treatment. Future studies including varying time

exposures and currents are necessary to more fully understand the effects

of electrocution on wood strength and appearance, especially for wood in

concealed locations.

Microwaves. Considerable variability in mortality was observed

in artificially infested boards treated by microwaves. Mortality at 3-d

and 4-wk post-treatment did not significantly exceed the 90 percent level

of efficacy (Tables 2 and 18). There were no significant differences in

termite mortality between the attic and "living space" at 3-d or 4-wk

post-treatment (P > 0.05). However there was considerable variance (SD) in

mortality especially among 1 by 4s in the attic and "living space" and 2 by

4s in the "living space." 1 by 4 test boards in the "living space" had

lower mortality values than 2 by 4s and 4 by 6s but this difference was not

significant (P > 0.05). Control mortality values were low (< 5 percent at

3-d post-treatment) and suggest high survivorship in test boards prior to

treatment. However, a 5-fold increase 4-wk post-treatment suggest elevated

mortality due to handling and natural causes (Table 18). Mortality values

among control boards of various size dimensions were not significant (P >

0.05).

The overall mortality value for naturally infested boards was 97.4

percent (Table 19). This mortality value significantly exceeded the 90 and

95 percent levels of efficacy. Forty-five survivors were found among three

boards containing live termites, none of which were alates.

The results of this study were mixed. Without a doubt, microwave

energy applied to infested wood will kill termites. Mortality of termites

in artificially infested boards approached 90 percent but did not exceed 90

percent with statistical certainty. Mortality of termites in naturally

infested boards was good, statistically exceeding the 95 percent level of

control. As with electrocution, definition of the extent of an

infestation, location of the infested wood, and access to the infested wood

are all critical to achievement of the desired level of mortality with

microwave treatments.

Visual signs of damage were noted for some artificial boards (Table

4). Minor warping of test boards was noted and 6 boards were burned, 2

severely (Table 4). For shielded ovens, there is no uniform heating of

materials in the microwave field due to internal oven reflection and

non-uniform absorption of energy (Locatelli & Traversa 1989). From the

current study, it appears that unshielded microwave devices also may

produce non-uniform heating of boards during treatment for termites.

Monitored microwave emissions were not detectable at the 9.1 m required

safe operating distance and were less than 6 mw/cm2 within 0.3 m of a

treated wall.

This is the first published report on the efficacy and safety of

microwaves for the control of drywood termites. This method of nonchemical

control appears to have promise as an effective spot-treatment technique.

However, more information is needed to determine the correct time necessary

to achieve the desired level of control and wood penetration of microwave

energy for varying levels of wattage output. Monitoring of temperature

changes in building materials during treatment could improve efficacy and

promoted increased safety.

Handling and Controls. During the course of investigation, over

86,000 termites were handled. I. minor, like most termites, are fragile

and excessive handling can result in mortality (REFERENCE?). Sources of

handling mortality include smashed individuals and miscounts (Table 20).

Less than 3 percent of all handled insects for treated artificially

infested boards resulted in non-treatment mortality. The greatest source

of handling mortality was from the smashing of individuals between the

veneer sections of boards. Boards placed in the subarea had significantly

more smashed individuals than the attic and drywall areas (F = test?).

Dragging boards in the subarea prior to installation was probably

responsible for the increased levels of smashed individuals as compared to

control boards. More secure closing of test boards might/could have

reduced this source of handling mortality.

Control boards were placed into the Villa Termiti, but removed

before treatment -- check hard copy. Handling mortality of control boards

was also low; less than 7 percent. For control boards, the greatest source

of handling error was missing individuals; these individuals could be the

result of miscounts or cannibalism. For this current study, missing

individuals were more likely to have resulted from cannibalism because

"gained individual" counts, another form of miscounts, were very low for

both treated and control boards. Since handling mortality was minimal, we

conclude that any post-treatment mortality observed was primarily due to

natural or delayed treatment effects, not experimental error.

For naturally infested boards, the accuracy of the detection

equipment used (Wood-Destroying Insect Detector®) was also investigated.

Over 94 percent (102/108) of treated, naturally infested boards contained

termites when dissected. Boards determined to contain active termite

infestations by acoustic emissions and used as controls did, in fact,

contain termites 100 percent of the time upon dissection (Table 21). False

positives occurred 17 percent of the time (3/18) (Table 21). Three of

these false positives were boards that contained 1, 2, or 18 live

individuals. Our work substantiates earlier claims on the potential use of

the Wood-Destroying Insect Detector® by identifying pieces of structural

lumber as actively infested by I. minor (Scheffrahn et al. 1993). However,

the authors reported a poor relationship between acoustical counts and

termite population density for detection experiments conducted with I.

synderi (Scheffrahn et al. 1993). From observations of the 140 naturally

infested boards included in this report, a significant correlation (r2 >

0.5) between detection level and termite number was found (Lewis & Haverty,

unpublished data). More technologically advanced acoustic emission devices

may be developed which could improve the predictability of termite

population density in naturally infested wood.

Conclusions

Over 90 percent of all test insects for both artificially and

naturally infested boards were killed during treatment. This high

mortality level attests to the fact that all techniques "work" to some

degree. Prior to testing in the Villa Termiti, all vendors claimed high or

total elimination of drywood termite infestations within homes. Test

results from whole-structure treatments for artificially and naturally

infested boards reveal that at the very highest standard of efficacy, 99

percent, only the fumigant gases demonstrated near 100 percent elimination.

Whole-structure treatment with heat was, however, very similar in efficacy

level to the fumigant gases. Perhaps improved application techniques or

the addition of synergists could elevate heat to higher levels of efficacy.

For localized treatments, 30-min @ 1.4 kg/min and 15-min @ 0.9

kg/min dosages of liquid nitrogen and long application times using

drill-and-pin techniques with electrocution were significantly efficacious

at the 95 percent level. Microwave treatments (750 W) were deemed

efficacious at the 95 percent level, but only when treating naturally

infested boards. Not efficacious, even at the 90 percent level, were

electrocution without drill-and-pin techniques and 8-min @ 0.9 kg/min

treatments of liquid nitrogen.

In general, monitored treatments fared better than non-monitored

treatments. Although damage may occur from fumigation, heat or microwaves,

it is a certainty for liquid nitrogen (repairs to drilled holes in wall

voids) and electrocution (drill-and-pin applications). The development of

improved termite monitoring devices in situ could also improve the

performance of all spot-treatment techniques. Field efficacy rates for all

available drywood termite control methods, including drill-and-treat with

chemicals, mode-of action, and damage to structures especially at the

micro-level are potential and important areas for future research. In

addition, standardization of acceptance levels of efficacy and damage to

structures and stricter oversight for advertising claims will be needed.

Acknowledgments

The authors wish to thank the many agencies, private firms,

institutions, and individuals that contributed to the study. These include

the Structural Pest Control Board of California for major funding, the Pest

Control Operators of California, Inc., and dozens of private pest control

firms for donations of money for construction of the Villa Termiti. A

special thanks to Director Frank Beall and staff of the Forest Products

Laboratory for accommodating property for the study. We would also like to

thank the tireless efforts of the laboratory crew: Steve Suoja, Edward

Dunbar, Calvin Fouche, Michelle Gaither, Lori Nelson, Carnet Williams, Gail

Getty, Peter Haverty, Ariel Power, Miwako Takano, Miguel Fernandez,

Salvador Rubio-Garcia, Daniel Gaither, Kirsten Copren, Lila Greb, Rebecca

Pollard, Ken Wong, Aikane Lewis, Gail Atilano, Mechelle Cochran, and Thien

Nguyen. Dr. Michael Rust and Eileen Paine from the University of

California at Riverside provided liquid nitrogen treatments. Sources of

drywood termites and naturally infested boards were provided by Ken

Abrahamian, Dr. Thomas Atkinson and dozens of pest control operators

throughout California. Statistical consultations were provided by Dr.

James Baldwin, Pacific Southwest Station, USDA Forest Service, Albany, CA.

The Wood-Destroying Insect Detector® was provided by DowElanco. Reviewers

of earlier drafts of this manuscript include: Dr. Ian Carmichael,

University of California, Berkeley; Dr. Richard Kramer, National Pest

Control Association, Dunn Loring, VA; Dr. Rudolf Scheffrahn, University of

Florida, Ft. Lauderdale, FL; Dr. James Baldwin, Pacific Southwest Station,

USDA Forest Service, Albany, CA. and Dr. Barbara Thorne, University of

Maryland, College Park, MD. Their comments and suggestions have greatly

improved the presentation and interpretation of this study. Lastly, the

authors wish to thank all participating vendors who, very graciously and at

their expense, conducted all treatments.

References Cited

Anonymous. 1990. California Statistical Abstract. California Department

of Finance, Sacramento. 204 p.

Anonymous. 1993. Manual for Vikane gas fumigant. DowElanco,

Indianapolis, Indiana.

Atkinson, T. H. 1994. Long Term Effects of Temperature and Humidity on

Survival, Differentiation, and Reproduction of Drywood Termites:

Preliminary Summary (unpublished report).

Atkinson, T. H. 1995. Efficacy of chemical and nonchemical treatments

against drywood termites and incidence of termite damage in southern

California (unpublished report).

Becker, G. 1967. Die Temperatur-Abhangigkeit der Frasstatigkeit einger

Termitenarten. Z. ange. Entomol. 60: 97-123.

Bennett, G. W., E. S. Runstrum & J. A. Wieland. 1983. Pesticide use in

homes. Bull. Entomol. Soc. Am. 29: 31-38.

Bess, H. A. & A. K. Ota. 1960. Fumigation of buildings to control the

dry-wood termite, Cryptotermes brevis. J. Econ. Entomol. 53(4): 503-510.

Bowler, K. 1981. Heat death and cellular heat injury. J. Thermal Biology

6: 171-178.

Brier, A. N. 1987. California homes: characteristics of decay and insect

attack. Wood Building Research Center Publication, Forest Products

Laboratory, University of California, Berkeley. 60 p.

Brier, A. N., W. A. Dost & W. W. Wilcox. 1988. Characteristics of decay

and insect attack in California homes. Calif. Agric. 42(5): 21-22.

Cicerone, R. J. 1987. Changes in stratospheric ozone. Science 237: 35-42.

Collins, M. S., M. I. Haverty, J. P. La Fage & W. L. Nutting. 1973.

High-temperature tolerance in two species of subterranean termites from the

Sonoran Desert in Arizona. Environ. Entomol. 2(6): 1122-1123.

Crocker, R. L., D. L. Morgan, & M. T. Longnecker. 1987. Effects of

microwave treatment of live oak acorns on germination and on Curculio sp.

(Coleoptera: Curculionidae) larvae. J. Econ. Entomol. 80: 916-920.

D'Ambrosio, G., G. Ferrara & A. Tranfaglia. 1982. Teratogenesis due to

microwaves in Tenebrio molitor (Coleoptera: Tenebrionidae) and Sitophilus

granarius (Coleoptera: Curculionidae). Influence of impulse modulation.

Boll. Lab. Entomol. Agrar. Filippo Silvestri 39: 3-9.

Del Estal, P., E. Vinuela, E. Page & C. Camacho. 1986. Lethal effects of

microwaves on Ceratitis capitata Wied. (Diptera: Trypetidae) Influence of

developmental stage and age. J. Appl. Entomol. 102: 245-253.

Dost, W. A., W. W. Wilcox & A. N. Brier. 1987. California structural pest

control: a diverse industry. Voice of the PCOC, Fall 1987: 10, 24.

Ebeling, W. 1983. The Extermax system for control of the western drywood

termite, Incisitermes minor. Etex Ltd., Las Vegas. 11 p.

Ebeling, W. 1990. Heat and boric acid: an example of synergism. Pest

Control Technology April 1990: 44-46.

Ebeling, W. 1994. The Thermal Pest Eradication System for structural pest

control. The IPM Practitioner 16(2): 1-7.

Ebeling, W. & C. F. Forbes. 1988. Sand barriers for subterranean termite

control. The IPM Practitioner 10(5): 23-28.

Ebeling, W. & R. E. Wagner. 1964. Built-in pest control. Pest Control

32(2): 20-32.

Forbes, C. A. & W. Ebeling. 1986. Update: liquid nitrogen controls

drywood termites. The IPM Practitioner 8(8): 1-4.

Forbes, C. A. & W. Ebeling. 1987. Update: use of heat for elimination of

structural pests. The IPM Practitioner 9(8): 1-5.

Forest Products Laboratory. 1987. Wood handbook: Wood as an engineering

material. USDA Forest Service Agric. Handb. 72; rev. 1987. 466 p.

Hall, A. V. 1988. Pest control in herbaria. Taxon 37(4): 885-907.

Hall, D. W. 1981. Microwave: a method to control herbarium insects.

Taxon 30(4): 818-819.

Haverty, M. I., J. P. La Fage & W. L. Nutting. 1974. Seasonal activity

and environmental control of foraging of the subterranean termite,

Heterotermes aureus (Snyder), in a desert grassland. Life Sciences 15:

1091-1101.

Heinrich, B. 1981. Insect Thermoregulation. John Wiley and Sons, New

York, NY.

Kenaga, E. E. 1957. Some biological, chemical and physical properties of

sulfuryl fluoride as an insecticidal fumigant. J. Econ. Entomol. 50(1):1-6.

Kofoid, C. A. 1934. Climatic factors affecting the local occurrence of

termites and their geographical distribution, pp. 13-21. In C. A. Kofoid

[ed.], Termites and Termite Control. Univ. Calif. Press, Berkeley.

Kramer, R. 1992. The methyl bromide controversy heats up. Pest

Management 11(7): 26.

La Fage, J.P., M. I. Haverty & W. L. Nutting. 1976. Environmental factors

correlated with the foraging behavior of a desert subterranean termite,

Gnathamitermes perplexus (Banks) (Isoptera:Termitidae). Sociobiology 2(2):

155-169.

Levenson, H. & G. W. Frankie. 1983. A study of homeowner attitudes and

practices toward arthropod pests and pesticides in three U.S. metropolitan

area, pp 67-106. In G. W. Frankie and C. S. Koehler [eds], Urban

Entomology: Interdisciplinary Perspectives. Praeger, New York.

Lewis, V. R. & R. L. Lemaster. 1991. The potential of using acoustical

emission to detect termites within wood, pp. 34-37. In M.I. Haverty & W.W.

Wilcox [tech. coords] Proceedings of the Symposium on Current Research on

Wood-Destroying Organisms and Future Prospects for Protecting Wood in Use,

September 13, 1989, Bend, Oregon. USDA Forest Service General Technical

Report PSW-128.

Lewis, V. R., R. L. Lemaster, F. C. Beall & D. L. Wood. 1991. Using AE

monitoring for detecting economically important species of termites in

California. International Research Group on Wood Preservation, Document

IRG/WP/2375.

Locatelli, D. P. & S. Traversa. 1989. Microwaves in the control of rice

infestants. Ital. J. Food Sci. No. 2: 53-62.

Lund, A. 1962. Subterraneans and their environment. Pest Control 30:

3034, 36, 60-61.

Mampe, C.D. 1990. Termites, p. 201-262. In A. Mallis [ed.], Handbook of

Pest Control. Franzak & Foster Co, Cleveland, Ohio.

Meikle, R. W., D. Stewart & O. A. Globus. 1963. Drywood termite

metabolism of Vikane fumigant as shown by labeled pool technique. J.

Agraic. Food Chem. 11(3): 226-230.

Nelson, W. O. 1977. Microwave di electric properties of insects and grain

kernels. J. Microwave Power 12: 39.

Nelson, S. O. & J. A. Payne. 1982. Pecan weevil Curculio caryae control

by di electric heating. J. Microwave Power 17: 51-56.

Osbrink, W. L. A., R. H. Scheffrahn, N.-Y. Su & M. K. Rust. 1987.

Laboratory comparisons of sulfuryl fluoride toxicity and mean time of

mortality among ten termite species (Isoptera: Hodotermitidae,

Kalotermitidae, Rhinotermitidae). J. Econ. Entomol. 80(5): 1044-1047.

Osbrink, W. L. A., R. H. Scheffrahn, R.-C. Hsu & N.-Y. Su. 1988. Sulfuryl

fluoride residues of fumigated foods protected by polyethylene film. J.

Agric. Food Chem. 36(4): 853-855.

Philbrick, C. T. 1984. Comments on the use of microwave as a method of

herbarium insect control: possible drawbacks. Taxon 33(1): 73-74.

Reagan, B. M., J.-H. Chiao-Cheng & N. J. Streit. 1980. Effects of

microwave radiation on the webbing clothes moth, Tineola bisselliella and

textiles. J. Food Prot. 43(8): 658-663.

Rosenberg, U. & W. Bögl. 1987. Microwave pasteurization, sterilization,

blanching, and pest control in the food industry. Food Technology. June

1987: 92-99.

Rust, M.K., E. O. Paine & D. A. Reierson. 1995. Laboratory evaluation of

low temperature for controlling drywood termites. (In preparation).

Rust, M. K., J. K. Grace, D. L. Wood & D. A. Reierson. 1988. The search

for new termite control strategies. Calif. Agric. 42(5): 15-18.

SAS Institute. 1994. SAS/STAT guide for personal computers, version 6.10

ed. SAS Institute, Cary, NC.

Scheffrahn, R. H., W. L. A. Osbrink, R.-C. Hsu & N.-Y. Su. 1987.

Desorption of residual sulfuryl fluoride from structural and household

commodities by headspace analysis using gas chromatography. Bull. Environ.

Contam. Toxicol. 39: 769-775.

Scheffrahn, R. H., R.-C. Hsu, W. L. A. Osbrink & N.-Y. Su. 1989a.

Fluoride and sulfate residues in foods fumigated with sulfuryl fluoride.

J. Agric. Food Chem. 37: 203-206.

Scheffrahn, R. H., R.-C. Hsu & N.-Y. Su. 1989b. Fluoride residues in

frozen foods fumigated with sulfuryl fluoride. Bull. Environ. Contam.

Toxicol. 43: 899-903.

Scheffrahn, R. H., R.-C. Hsu & N.-Y. Su. 1990. Evaluation of polymer film

enclosures as protective barriers for commodities from exposure to

structural fumigants. J. Agric. Food Chem. 38(3): 904-908.

Scheffrahn, R. H. and N.-Y. Su. 1992. Comparative toxicity of methyl

bromide against ten nearctic termite species (Isoptera: Termopsidae,

Kalotermitidae, Rhinotermitidae). J. Econ. Entomol. 85(3): 845-847.

Scheffrahn, R. H., L. Bodalbhai, & N.-Y. Su. 1992. Residues of methyl

bromide and sulfuryl fluoride in manufacturer-packaged household foods

following fumigation. Bull. Environ. Contam. Toxicol.48: 821-827.

Scheffrahn, R. H., W. P. Robbins, P. Busey, N.-Y. Su & R. K. Mueller.

1993. Evaluation of a novel, hand-held, acoustic emissions detector to

monitor termites (Isoptera: Kalotermitidae, Rhinotermitidae) in wood. J.

Econ. Entomol. 86(6): 1720-1729.

Scheffrahn, R. H., G. S. Wheeler, and N.-Y. Su. 1995. Synergism of methyl

bromide and sulfuryl fluoride toxicity against termites (Isoptera:

Kalotermitidae, Rhinotermitidae) by admixture with carbon dioxide. J.

Econ. Entomol. 88(3): 649-653.

Scheffrahn, R. H., C. L. Bloomcamp & N.-Y. Su. 199?. Indoor airborne

residues of methyl bromide and sulfuryl fluoride following aeration of

fumigated houses. (In review/press??).

Smythe, R. V. & L. H. Williams. 1972. Feeding and survival of two

subterranean termite species at constant temperature. Ann. Entomol. Soc.

Am. 65(1): 226-229.

Steel, R. G. F. & J. H. Torrie. 1960. Principles and Procedures of

Statistics. McGraw-Hill Book Company, Inc. New York.

Su, N.-Y. & R. H. Scheffrahn. 1986. Field comparison of sulfuryl fluoride

susceptibility among three termite species (Isoptera: Kalotermitidae,

Rhinotermitidae) during structural fumigation. J. Econ. Entomol. 79:

903-908.

Su, N.-Y. & R. H. Scheffrahn. 1990. Economically important termites in

the United States and their control. Sociobiology 17: 77-94.

Tallon, J. C. 1992. Non-toxic method of exterminating insects. U. S.

Patent 5,165,199.

Thoms, E. M. & R. H. Scheffrahn. 1994. Control of pests by fumigation with

Vikane gas fumigant (sulfuryl fluoride). Down to Earth 49(2): 23-30.

Tilton, E. W. & H. H. Vardell. 1982a. An evaluation of a pilot-plant

microwave vacuum drying unit for stored-product insect control. J. Ga.

Entomol. Soc. 17(1): 133-138.

Tilton, E. W. & H. H. Vardell. 1982b. Combination of microwaves and

partial vacuum for control of four stored-products insects in stored grain.

J. Ga. Entomol. Soc. 17(1): 106-112.

Watters, F. L. 1976. Microwave radiation for control of Tribolium

confusum in wheat and flour. J. Stored Prod. Res. 12: 19-25.

Wilcox, W. W. 1979. Decay of wood in structures. Calif. Agric. 33: 32-33.

Figure Captions

Figure 1. Tongue depressor holding chambers used for maintaining groups of

Incisitermes minor prior to testing or after testing to measure 4-wk

mortality.

Figure 2. Villa Termiti used to test fumigation techniques and nonchemical

alternatives to fumigation for control of drywood termites. The Villa

Termiti is symmetrical with all four sides structurally identical.

Figure 3. Sagittal view of Villa Termiti showing test board placement

locations for attic, drywall, and subarea.

Figure 4. Sagittal view of foundation showing test board placement

locations for tests on or near the sill plate.

Figure 5. Douglas-fir "2 by 4" cut so that artificial infestations of 25

I. minor pseudergates and nymphs could be placed in each of three galleries.

Figure 6. Thermocouple placement for attic, drywall, and subarea treated

by excessive heat.

Figure 7. Schematic drawing of drywall area in Villa Termiti. Shaded

circles indicate points of introduction for liquid nitrogen. Location of

thermocouples are indicted by arrows.