Abstract
AbstractResistance to pyrethroid insecticides and dichlorodiphenyltrichloroethane (DDT) was investigated in the napts (no action potential, temperature sensitive) mutant of Drosophila melanogaster. In surface contact bioassays, the napts strain showed threefold resistance to deltamethrin at the LC50 level when compared to susceptible Canton‐S flies. Cross‐resistance was also observed to DDT and the pyrethroids NRDC 157 [3‐phenoxybenzyl [1R,cis]‐3‐(2,2‐dibromovinyl)‐2,2‐dimethylcyclopropanecarboxylate], fenfluthrin, and MTI‐800 [1‐(3‐phenoxy‐4‐fluorophenyl)‐4‐(4‐ethoxyphenyl)‐4‐methylpentane]. The onset of intoxication by pyrethroids in napts flies was markedly delayed, a finding that is consistent with the existence of a resistance mechanism involving reduced neuronal sensitivity. Resistance at the level of the nerve was confirmed by electrophysiological recordings of spontaneous and evoked activity in the dorsolongitudinal flight muscles of poisoned flies. Preparations from napts insects treated with fenfluthrin displayed longer latencies to the appearance of spontaneous activity and also an absence or reduction in burst discharges compared to equivalent preparations from susceptible individuals. These results are discussed in light of competing hypotheses concerning the mechanism underlying knockdown resistance and reduced nerve sensitivity in insects.
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