Sublethal Exposure to Insecticides Disrupts Pheromone Communication and Reduces Fertility in the Cotton Boll Weevil ( Anthonomus grandis grandis )

ABSTRACT

The objective of this work was to evaluate the effects of sublethal exposure to the insecticides malathion and beta‐cyfluthrin on the pheromone perception and emission by the cotton boll weevil [ Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae)]. The potential impact of sublethal exposure on this species' population growth was also determined using fertility table parameters. Males and females were exposed to malathion (100 g a.i./L) or beta‐cyfluthrin (25 g a.i./L) for 1 min in a glass Petri dish. The response of pesticide‐exposed and unexposed insects to their aggregation pheromone (grandlure) was evaluated in a Y‐tube olfactometer, and pheromone production was assessed. In order to evaluate the possible reproductive effects, the couples remained isolated for 48 h, and the females were subsequently evaluated until their death. For reproductive assays, four mating‐pair treatments were established: (1) both sexes unexposed; (2) exposed males paired with unexposed females; (3) exposed females paired with unexposed males; and (4) both sexes exposed. Insects exposed to both insecticides did not respond to their aggregation pheromone during the first 24 h after exposure, whereas unexposed weevils showed a clear behavioral response. However, insecticide‐exposed males did not show reduced pheromone production compared to unexposed males. Sublethal insecticide exposure lowered the net reproductive rate ( R ₀ ) and the intrinsic rate of increase ( r _m ) for the cotton boll weevil. These findings suggest that sublethal insecticide exposure may suppress boll weevil population growth while potentially compromising the reliability of pheromone‐based monitoring programs in intensively treated cotton fields.