EVALUATION OF SIX TECHNIQUES FOR CONTROL OF THE WESTERN DRYWOOD TERMITE (ISOPTERA: KALOTERMITIDAE) IN STRUCTURES
VERNARD R. LEWIS AND MICHAEL I. HAERTY
The damage caused by wood-destroying insects has an important economic effect. Nationwide, the cost of control and repair of damage nears $5 billion per year; the outlay in California and Hawaii exceeds $1 billion per year (Brier et al. 1988, Su and Scheffrahn 1990). In California, subterranean and drywood termites are responsible for >95% of all costs resulting from wood-destroying insects (Brier 1987, Rust et al. 1988). Damage by drywood termites is more common in southern California (Wilcox 1979).
For many years, the standard treatment for control of drywood termites has been fumigation with methyl bromide (MB) or sulfuryl fluoride (SF). These fumigants are effective against a variety of termite species in laboratory tests (Bess and Ota 1960, Osbrink et al. 1987, Scheffrahn and Su 1992). The theoretical dosages for MB and SF (3.5 and 3.0 mg/m3, respectively) are similar (Stewart 1957). Depending on label instructions and conditions, the amount of fumigant used to treat a typical home ranges from app. 5 - 20 kg (Scheffrahn et al. 1995). For CO2-synergized MB, an additonal 106 kg of carbon dioxide (app. 10% of the total volume of structure) are also required (Scheffrahn et al. 1995). The use of fumigants is considered a "whole-structure treatment" (the simultaneous treatment of all wooden members and extensive or difficult to access infestations) and should completely eradicate drywood termites within a strecture (Scheffrahn and Su 1994). Unfortunately, there is relatively little scientific information on the effectiveness of fumigation from field studies.
The public is showing increased interest in non-chemical insect control in homes (Bennett et al. 1983, Levenson and Frankie 1983). The nonchemical alternatives presently marketed for control of drywood termites currently includes excessive heat or cold, electrocution, and microwaves. With the exception of excessive heat, the remaining non-chemical treatments are classified as "local or spot treatment" applications (Scheffrahn and Su 1994). These treatments are often restricted to a single spot within a board or small group of boards.
There is limited published research on any of the alternative control methods presented in this article. Forbes and Ebeling (1987) found that pseudergates of the western drywood termite, Incisitermes minor (Hagen), died if exposed to 51 degrees C for >10 min during laboratory studies. When the temperature within wood was maintained at greater or equal to 48 degrees C for at least 30 min in field demonstrations, Ebeling (1994) reported 100% mortality for I. minor pseudergates. Forbes and Ebeling (1986) reported that I. minor individuals died within 5 min at temperatures between -18.5 and -19.4 degrees C. Rust et al. (1995) found that exposure of nymphs and alates in wooden blocks to temperatures below -21.4 degrees C resulted in 100% mortality. Forbes and Ebeling (1986) were the first to demonstrate the spot-application method for killing drywood termites using liquid nitrogen (-180 degrees C) in wall voids. There are no published reports on the efficacy of electrocution under field conditions. Ebeling (1983) reported empirical observations of routine commerical treatments. Mortality from one observed treatment was 74, 81.3, and 96.3% at 0, 26, and 57 d after treatment. Although highly speculative, Ebeling (1983) attributed delayed mortality to the destruction of intestinal protozoans.
Microwaves have been investigated as a means of destroying insects in dried foods, nuts, and stored grain (Watters 1976; Nelson 1977; Reagan et al. 1980; D'Ambrosio et al. 1982; Nelson and Payne 1982; Tilton and Vardell 1982a, b; Del Estal et al. 1986; Rosenberg and Bögl 1987; Locatelli and Traversa 1989) and for preserving textiles and museum specimens (D. Hall 1981, Philbrick 1984, A. Hall 1988). Thus far, there have been no published reports on effects of microwaves on termites.
Nonchemical methods are currently being marketed as replacements for structural fumigation for drywood termite control. Several of these methods are now being applied by pest control companies in several states. Here we report the test results of 2 types of fumigation and 4 methods marketed as alternatives to whole-structure fumigation. We tested each method against 2 levels of efficacy: 90 and 99% at 3 d and 4 wk after treatment.