Off-Season Diet and Ecology of the Boll Weevil Influence Long-Term Malathion Susceptibility

Background: The cotton boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), is a major pest of cotton that causes significant yield losses and costly control measures. As a cotton-specialized species, its population dynamics are heavily influenced by environmental conditions and management practices during the off-season. This study examined the effects of off-season food sources on adult survival, reproductive capacity, and susceptibility to malathion in the last generation before the off-season and in the generation entering the next planting season. Methods: Females were fed diets representing off-season conditions (cotton terminals and pollen) and the standard diet (flower buds), and then evaluated for survival, copulation, sperm viability, and egg production. Concentration–mortality bioassays determined malathion susceptibility before and after the off-season. Results: Female survival was lowest in those fed cotton terminals, while pollen and flower buds supported higher survival rates. The likelihood of copulation and sperm viability remained similar among diets after 60 days, or up to 100 days in surviving females; however, females fed flower buds had more eggs in their oviducts. Females that mated early maintained viable sperm up to the end of the 100-day assessment period. Populations collected after the off-season were more susceptible to malathion than those collected at the end of the growing season. Conclusions: Food restrictions and reduced malathion exposure during the off-season may contribute to a reversion toward boll weevils’ susceptibility to malathion. Overall, the findings highlight the importance of the fallow period and proper management of residual off-season populations for effective long-term boll weevil control, confirming malathion’s continued viability as a management tool.