Lethal and sublethal effects of various insecticides on the immature stages of the solitary egg parasitoid, Telenomus busseolae

Telenomus busseolae Gahan (Hymenoptera: Scelionidae) is the most effective egg parasitoid of corn borers, Sesamia spp. (Lepidoptera: Noctuidae). A balanced pest management requires the use of insecticides compatible with T. busseolae since relying solely on the parasitoid may prove inadequate in controlling pest outbreaks. This study investigated the lethal and sublethal effects of chlorantraniliprole, imidacloprid, indoxacarb, lambda-cyhalothrin, lufenuron, malathion, and thiamethoxam + lambda-cyhalothrin, at various concentrations on emergence rate and fecundity of treated generation as well as emergence rate and sex ratio of offspring generation. The experiments were performed by immersing the host eggs with the parasitoid, encompassing its early larval, late larval, and pupal stages into the insecticide solutions.

All concentrations of the insecticides reduced emergence rate in the treated generation, with the pupal stage being most vulnerable except for controversial effects of lambda-cyhalothrin and immature stage-independent effects of imidacloprid. The insecticides, at least one of the concentrations, negatively affected parasitoid fecundity regardless of a consistent pattern across immature stages. The insecticides did not affect the tested attributes of offspring generation except for that imidacloprid reduced female offspring numbers, and malathion decreased emergence rates.

This study provides insights into immature stage-specific susceptibility and fecundity responses of treated generation along with potential impacts on subsequent generation, highlighting the necessity of prudent insecticide usage within the context of integrated pest management strategies (IPMs) in maize fields. Additionally, it underscores the urgency of performing field studies to ascertain actual toxicological scenarios.