Custo adaptativo associado à resistência de Spodoptera frugiperda (J. E. Smith) (Lepidoptera:Noctuidae) a metomil

Abstract

The incorrect use of synthetic chemical insecticides has shown control failures and promoted the selection of populations of resistant pest species, such as Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), a species that represents a constant threat to world agriculture. Insect resistance to insecticides may have an adaptive cost, impairing their development compared to susceptible individuals in the absence of insecticide selection pressure. Identifying the presence or absence of this cost is crucial for the adoption of resistance management strategies. Thus, the objective was to evaluate the existence of adaptive costs associated with the resistance of S. frugiperda to Methomyl. The susceptible population (SUS) of S. frugiperda was collected in the field and kept at the Laboratory of Applied Entomology (LEA) of UFC. To obtain the Methomyl-resistant population, part of the number of caterpillars of the SUS population started to be fed with corn leaves treated with the active ingredient Methomyl, being kept under selection pressure, exposed to LC50, for six generations. The parameters of the life and fertility table of the two populations of S. frugiperda were evaluated. The longevity of each life stage (larva-pupa, pupa-adult), pupal mass and biological parameters such as survival rate, sex ratio, fertility, fecundity and resistance ratio (RR) were analyzed. According to the results, the LC50 of Methomyl obtained for the susceptible population was lower than the LC50 of the resistant population after 6 generations, indicating a response to selection pressure with Methomyl. The population presents low resistance, according to the resistance ratio value. The values for the duration of the larval, larva-adult period differed, being higher in the methomyl resistant population, and the generation time was longer in the resistant population by 3.3 days. Pupal mass was lower in the resistant population. The lowest percentage of survival of the phases was observed in the resistant population. The parameters of the fertility table: Intrinsic (r) and finite (λ) rate of increase and net reproductive rate (R0) ratio of the resistant population were significantly lower. The Rf value, based on the net reproductive rate, was less than 1, which indicates the presence of adaptive costs in the resistant population of S. frugiperda. A reduction in fertility was observed in the resistant population compared to the susceptible population. It is possible to conclude that there is an adaptive cost associated with resistance to Methomyl in the population of S. frugiperda studied.