Safety Evaluation of Chemical Insecticides to Tetrastichus howardi (Hymenoptera: Eulophidae), a Pupal Parasitoid of Spodoptera frugiperda (Lepidoptera: Noctuidae) Using Three Exposure Routes

SIMPLE SUMMARY: Spodoptera frugiperda is an important pest in many crops worldwide, causing substantial economic losses. The main control strategies are biological control and chemical control. However, pesticides also have varying degrees of toxicity to parasitic wasps in the field. In this study, we evaluate the safety of insecticides for Tetrastichus howardi, an important pupal parasitoid of S. frugiperda. We tested the toxicity of six major control insecticides against the parasitic wasps. Indoxacarb was the less toxic pesticide to T. howardi due to its toxicity’s low-risk quotient (7.43). Furthermore, we used three methods to simulate the side effects of different concentrations of indoxacarb on T. howardi. The exposure of adults to pesticide residues on the glass tube was the most significant in inhibiting development and fecundity. Moreover, T. howardi had a lower parasitism rate and emergence rate with the higher pesticide concentrations. Overall, our study showed that different exposure patterns and concentrations of pesticides have varying degrees of side effects on T. howardi. Even if the pesticide residues are low, such exposures can affect the life cycle of parasitic wasps, affect their population establishment, and thus affect pest control. This study guides a more scientific and comprehensive pesticide application and releases natural enemies. ABSTRACT: Spodoptera frugiperda has become a major pest in many crops worldwide. The main control strategies are biological and chemical controls. However, pesticides have varying degrees of toxicity to parasitic wasps in the field. To integrate chemical and biological controls, we evaluated the safety of insecticides to Tetrastichus howardi, an important pupal parasitoid of S. frugiperda. This study assessed the toxicity of six major control insecticides (emamectin benzoate, chlorfenapyr, indoxacarb, chlorantraniliprole, bisultap, and lufenuron) to T. howardi based on risk quotient. The results showed that indoxacarb had the lowest risk quotient (RQ = 7.43). Then the side effects of three sublethal concentrations (LC(20), LC(30), LC(40)) of indoxacarb were tested using three methods (1. Adult exposure to pesticide residues on the glass tube; 2. Adult exposure to pesticide residues on the host; 3. Larval exposure to pesticides through host exposure). Overall, T. howardi had a lower parasitism rate and emergence rate with the higher pesticide concentrations. Furthermore, among three methods, the adult exposure to pesticide residues on the glass tube was the most efficient in inhibiting the parasitism rate, and impairing the emergence rate and the offspring female/male ratio. This study guides a more scientific and comprehensive application of pesticides and releases natural enemies in the field.