A systemic bioassay to determine susceptibility of the pepper weevil, Anthonomus eugenii Cano (Coleoptera: Curculionidae) to cyantraniliprole and thiamethoxam

Cyantraniliprole (Cyazypyr™) is the second insecticide in the new anthranilic diamide class with xylem-systemic properties and a novel mode of action. Thiamethoxam is a neonicotinoid insecticide that is used to manage the pepper weevil (Anthonomus eugenii Cano). A systemic bioassay method, using pepper seedlings, was developed to determine baseline toxicity data for both insecticides using a susceptible laboratory strain of the pepper weevil. Results demonstrated that cyantraniliprole and thiamethoxam inhibited daily feeding. After 5 days of exposure, pooled LC50, LC95, and slope values were 7.06 mg ai L−1, 195.2 mg ai L−1, and 1.14 (SE = 0.132) for cyantraniliprole and 0.53 mg ai L−1, 1.91 mg ai L−1, and 2.93 (SE = 0.435), for thiamethoxam. After 7 days of exposure, analysis of the pooled data for three bioassays with cyantraniliprole, resulted in LC50, LC95, and slope values of 2.12 mg ai L−1, 30.2 mg ai L−1, and 1.43 (SE = 0.132), whereas a single bioassay with thiamethoxam generated LC50 and LC95, and slope values of 0.44 mg ai L−1, 1.22 mg ai L−1, and 3.72 (SE = 0.842), respectively. The development of the present bioassay method permits the evaluation of the toxicity of systemic insecticides to pepper weevil adults. Both cyantraniliprole and thiamethoxam inflicted mortality on adults, although the latter appeared to be more potent. At the LC50 and LC95 levels, thiamethoxam was 13 and 5 times, respectively, more potent than cyantraniliprole after 5 days of exposure and 100 and 5 times more potent after 7 days of exposure. Both products appeared to suppress feeding damage of pepper weevils. The bioassay method developed and the information generated on laboratory susceptibility in the present study represents the basis for the use of the method for monitoring changes in susceptibility and for confirming or refuting questions of resistance in the pepper weevil.