Dynamics of flubendiamide resistance in Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae)

Chemical insecticides are used to manage Chrysodeixis includens in soybean (Glycine max (L.) Merrill). Flubendiamide was selected for this study due to its widespread application and its role as a key insecticide for controlling lepidopteran pests, including C. includens. Frequent insecticide use exerts high selection pressure that can cause control failure caused by an increased frequency of resistant insects in the population. However, in the absence of selection pressure, resistant insects may exhibit fitness costs that can restore susceptibility. Therefore, this study aimed to examine the stability of C. includens resistance to flubendiamide and to evaluate the associated fitness costs. Resistance dynamics were evaluated for eight generations without selection pressure by flubendiamide, using three populations: resistant (CiResFlu), susceptible (SUSCI-15), and a mixture of 50% SUSCI-15 and 50% CiResFlu (SusRes). In each generation, a subset of insects were exposed to 0.5053 mu g a.i. cm-2. To investigate the fitness costs, the biological parameters of the life cycle of the SUSCI-15 and CiResFlu populations were compared, and these parameters were used to construct the fertility life table. In the absence of selection pressure from flubendiamide, the CiResFlu population reverted to susceptibility. Based on the evaluation of the duration and viability of immature and adult stages and the estimation of parameters of the fertility life table, no adaptive costs were detected between the resistant and susceptible populations. Thus, flubendiamide resistance in C. includens is unstable, and no fitness costs were observed.