|Woodson, W. - USDA-ARS-SRRC|
Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 8, 2002
Publication Date: N/A
Interpretive Summary: Subterranean termite damage and control efforts cost Americans an estimated 2 billion dollars annually. The Formosan subterranean termite was introduced into the United States shortly after World War II and is considered the most serious threat to wood structures in the U.S. Although insecticides have been used to control subterranean termites for decades, very little research has been conducted on their detoxification systems or relative susceptibilities to insecticides. It is crucial to effective control that we know the relative insecticide susceptibility among different colonies of termites. Therefore, scientists at the Center for Medical, Agricultural and Veterinary Entomology and Southern Region Research Center examined insecticide susceptibility among 20 colonies of Formosan subterranean termites sampled from the New Orleans area. Interestingly, all colonies were equally susceptible to the insecticides evaluated. Furthermore, the detoxification systems in these insects, although very competent, were essentially similar among all colonies examined. These data suggest that increased tolerance to insecticides is not occurring in the Formosan subterranean termite.
Technical Abstract: Coptotermes formosanus Shiraki worker termites were sampled from twenty locations in the City Park area of New Orleans, LA. The termites were subsequently assayed to determine their susceptibility to cypermethrin, chlordane, and chlorpyrifos and detoxification enzyme activity. Cypermethrin was most toxic against Formosan subterranean termite workers, chlorpyrifos exhibited intermediate toxicity and chlordane was least toxic A comparison of insecticide susceptibility between the most and least tolerant colonies revealed 1.9-, 1.7- and 1.8-fold differences in susceptibility for cypermethrin, chlorpyrifos and chlordane, respectively. As with the bioassay data, although significant differences were noted, a great deal of overlap was observed among the colonies for total cytochrome P450 content (difference of 2.2-fold between high and low value) aldrin epoxidation (3.6-fold) and cytosolic esterase (3.9-fold) activities. No significant differences were observed among the colonies for methoxyresorufin O-demethylase or glutathione S-transferase activities. Conversely, microsomal esterase activity varied greatly; a 38-fold difference was observed between the most (Cf1776) and least (Cf1387) active colonies. However, no significant correlation was observed between insecticide susceptibility and microsomal esterase activity. In fact, no significant correlations were observed between any of the enzyme activities measured and insecticide susceptibility. These results are discussed in the context of insecticide selection and future control effectiveness.