INHIBITION OF SEX-PHEROMONE COMMUNICATIONS OF TRICHOGRAMMA-BRASSICAE (HYMENOPTERA) BY THE INSECTICIDE CHLORPYRIFOS

Biological control agents such as entomophagus insects (e.g., Trichogr amma sp.) are important components of integrated pest management (IPM) programs. Because pesticides are also an important component of IPM p rograms, it is essential to understand how biological control agents a re affected by pesticides and how these effects may affect the effecti veness of the biological control agents. Contrary to most insect speci es that use volatile pheromones for mate location, T. brassicae is one of the few species using a substrate-borne sex pheromone for mating. In this work we determined the effects of an organophosphorus insectic ide, chlorpyrifos, on sex pheromone reception by males and emission by virgin females. The insects used in the pheromone tests were survivor s from an acute toxicity test in which individuals were exposed to a d ose of chlorpyrifos equivalent to a 20% lethal dose. Males that surviv ed the insecticide exposure spent much less time on the area marked wi th the female pheromone than control males (mean choice indexes, 0.46 [0.34 SD] vs 0.70 [0.25 SD], p < 0.001). The kinetics of the response of males to marking by control and treated females indicated that chlo rpyrifos decreased the emission of sex pheromone by females surviving the insecticide. Therefore, chlorpyrifos inhibited pheromone reception by males and decreased pheromone emission by virgin females. These re sults are interpreted in the context of sex pheromone regulation by th e nervous system of insects and according to the mode of action of chl orpyrifos. Extensions of these results on actual work on sex pheromone , the use of pheromone traps, and the population biology of Trichogram ma sp. are discussed.