Boletín de la AeE

Most insect species use volatile pheromone for mate location (Hansson, 1995). While volatile and contact sex pheromones have been found in several parasitoids (Eller et al., 1984; Mohamed and Coppel, 1987), little is known about the role of substrate-borne chemicals in sexual communication. Here we report the existence of a substrate-borne sex pheromone laid down by virgin female Trichogramma brassicae, an egg parasitoid of various lepidopteran pests. Moreover, evidences that insecticides interact with communication using sex pheromone were obtained.

For the experiments, one female was first allowed to walk for 30 min in one half of an arena and removed. Then a male was introduced and allowed to move within the cutiré arena. Its moves were recorded by a computerized video tracking device. Results demonstrated that virgin females (<1 or 5 days oíd) deposit chemicals that are attractive for males whatever their own mating status. Male response decreases over time but is always significant for the 8 min of videotracking, even when male response is tested 15 min after the end of marking. Hexane extraéis also induce a positive response of males. On the other hand, the arrestment response of males to female pheromone is greatly reduced when they survived an LD20 of chlorpyrifos, an organophosphorus insecticide. Furthermore, the kinetics of the response of males to marking by control and treated females, indicate that chlorpyrifos decreases the emission of sex pheromone by females surviving the insecticide.

While sublethal effects of insecticides on pest insects that communicate with volatile pheromones have been well documented in moths (Floyd and Crowder, 1981; Linn and Roelofs, 1984; Haynes and Baker, 1985; Moore, 1987; Clark and Haynes, 1992), our work is the flrst evidence of sublethal effects of an insecticide on substrate-borne sex pheromone Communications in a natura! enemy. Knowing that organophosphorus insecticides are widely used in agriculture and actively particípate to environmental pollution by pesticides (Lartiges and Garrigues, 1995), one can imagine the possible impact for the population biology of Trichogramma.