Electrophysiological study of the effects of deltamethrin, bioresmethrin, and DDT on the activity of pheromone receptor neurones in two moth species

Abstract

Electrophysiological techniques were used to study the effects of deltamethrin, bioresmethrin, and DDT on the olfactory system of Mamestra suasa and M. brassicae male moths (Noctuidae). Direct applications on the antenna of sublethal doses of pesticides were found not to modulate the activity of olfactory neurones. Thus lethal doses of the insecticides were applied topically in acetone solution on the abdomen of individuals. None of the three insecticides assayed modified the amplitude of EAG or receptor potentials in response to pheromone stimulations. In return, action potential initiation was susceptible to the insecticides. Deltamethrin inhibited both the spontaneous firing activity and that following pheromone or electrical stimulations. Under the influence of DDT olfactory neurones emitted bursts of impulses spontaneously in place of single spikes and discharged bursts of spikes in high frequency in response to pheromone stimulations instead of the usual regular volley. Despite the change of the firing pattern induced by DDT, the sensitivity and the specificity of the olfactory system remained unchanged. Bioresmethrin modified neither the neurone activity at rest nor the specificity of pheromone receptor neurones. In contrast, applications of this pyrethroid significantly reduced the number of action potentials emitted in response to pheromone stimulations. The differences in effects of deltamethrin, DDT, and bioresmethrin on the activity of pheromone receptor neurones are discussed on the basis of studies carried out both on the central and the peripheral nervous system.