Fitness costs and biochemical implications of spinetoram resistance in Earias vittella under long-term selection

This study investigates the fitness costs and biochemical implications associated with spinetoram resistance in Earias vittella (Lepidoptera: Noctuidae), a major cotton pest in Pakistan. Three experimental approaches were employed: (i) evaluation of fitness costs using life table parameters, (ii) assessment of insecticide-synergist interactions, and (iii) analysis of biochemical changes in resistant populations. Spinetoram-selected populations (SPINE-SEL) were compared with an unselected susceptible population (UNSEL). The results revealed significant fitness costs in the resistant populations. Developmental durations were markedly prolonged, with total development time increasing from 23.2 days in the unselected population to 30.4 days in the resistant population. Fecundity was significantly reduced, with susceptible females laying an average of 295.6 eggs compared to 197.4 eggs in resistant females. Mating success was also lower in resistant populations (56%) than in the unselected controls (82%). Biochemical assays indicated significantly elevated activities of detoxification enzymes, including mixed-function oxidases (MFOs), glutathione S-transferases (GSTs), and general esterases, in the resistant populations. Synergist bioassays revealed a 6.8-fold increase in spinetoram toxicity when combined with piperonyl butoxide (PBO) against resistant strains, highlighting the potential of synergists to mitigate resistance. Overall, these findings demonstrate substantial metabolic and reproductive trade-offs associated with spinetoram resistance and underscore the importance of integrated pest management strategies for the sustainable control of E. vittella in Pakistan.