Genética da resistência de Spodoptera frugiperda (J. E. Smith, 1797) a clorpirifós e resistência cruzada com outros inseticidas

Abstract

The fall armyworm, Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae), is a polyphagous species of global relevance due to the damage it inflicts to agricultural crops and its ability to evolve resistance to control tactics. In this study, a genotype of S. frugiperda resistant to chlorpyrifos (acetylcholinesterase inhibitor), was selected from a field population (collected in an area with a history of control failures by chlorpyrifos). After selection, studies were carried out to characterize the inheritance of resistance, estimate fitness costs, evaluate cross-resistance with other modes of action and mechanisms of resistance using synergists. In the resistance inheritance study, dose-response curves were obtained applying chlorpyrifos in topical bioassays in the resistant (Clorp-R), susceptible (Sus) and F1 progeny from reciprocal crosses (heterozygotes). To assess cross-resistance, the Clorp-R and Sus genotypes were exposed to acephate, thiodicarb, methomyl, chlorfenapyr, flubendiamide, methoxyfenozide, spinetoram and teflubenzuron. To evaluate mechanisms of resistance, larvae from Clorp-R genotype were previously exposed to synergists piperonyl butoxide (PBO), diethyl maleate (DEM) and S,S,S-tributyltriphosphorotrithioate (DEF), and then received doses of chlorpyrifos. The fitness costs of resistance were estimated by comparing the biological parameters of the Clorp-R, Sus and heterozygotes in leaves of cotton, maize, soybean, and oats. The LD50 values of chlorpyrifos for the Clorp-R and Sus genotypes were 24,26 and 0,023 μg a.i./larva, respectively, representing a resistance ratio >1050-fold. The LD50 values of chlorpyrifos for the heterozygotes were 3,34 and 4,00 μg a.i./larva, suggesting that resistance is autosomally inherited. The chlorpyrifos resistance in FAW was influenced by few genes, with the minimum number of segregations being 1.74 and 1.88. On chlorpyrifos-sprayed plants and leaves, Clorp-R and heterozygotes genotypes showed >95% and >52% survival, respectively, whereas the Sus genotype had no survival, indicating that the resistance is incompletely dominant at the field rate of chlorpyrifos. The Clorp-R genotype presented some cross-resistance to acephate, but low cross-resistance to thiodicarb, methomyl, chlorfenapyr, flubendiamide, methoxyfenozide, spinetoram, and teflubenzuron. The synergists did not have relevant effects on the Clorp-R genotype, suggesting a minor role for metabolic resistance. It was also found that the Clorp-R genotype showed fitness costs of the resistance in all host plants evaluated. In summary, the inheritance of resistance to chlorpyrifos in S. frugiperda is autosomal, incompletely dominant, polygenic and associated with fitness costs. Low cross-resistance between chlorpyrifos and insecticides with different modes of action occurs in S. frugiperda. Therefore, performing the rotation of modes of action is a strategy to delay the evolution of S. frugiperda resistance to chlorpyrifos and other insecticides.