Sublethal insecticide-induced hormesis effects on developmental traits and antioxidant defense in the key biocontrol agent <i>Trichogramma japonicum</i> (Ashmead)

Abstract Background: The diamide insecticide chlorantraniliprole is widely used in rice fields to control lepidopteran pests and is less toxic to non-target natural enemies. The egg parasitoid Trichogramma japonicum (Ashmead) is a key natural enemy deployed against these pests. However, sole reliance on T. japonicum is often insufficient for effective control and necessitates Integrated Pest Management tactics. Methods: Our study focused on the lethal and sublethal effects of chlorantraniliprole on T. japonicum , assessing its impact on growth, reproduction, oxidative stress, and physiological responses across two consecutive generations (G 1 and G 5 ). The T. japonicum adults were exposed to sublethal (LC 5 = 0.00001 mg a.i. L −1 , LC 30 = 0.023 mg a.i. L −1 ) and lethal (LC 50 = 0.972 mg a.i. L −1 ) concentrations of chlorantraniliprole over five generations (G 1 to G 5 ). Results: Exposure of T. japonicum adults to sublethal concentrations of chlorantraniliprole resulted in a marked enhancement in oviposition duration, longevity, and fecundity in the G 5 generation relative to the G 1 generation. The population parameters also exhibited significant enhancement at both concentrations of chlorantraniliprole (LC 5 and LC 30 ) in G 5 compared with the G 1 generation. Antioxidant activity (CAT and GPX enzyme activity) and the nutritional profile in T. japonicum depict a significantly higher response to the LC 30 of chlorantraniliprole in both generations . Sublethal concentrations exhibited less MDA content in T. japonicum adults compared with the median lethal concentration (LC 50 ). Conclusions: These findings support the hypothesis of hormesis. Therefore, Chlorantraniliprole-induced hormesis may favor parasitoid fitness in a consecutive generations, thereby potentially improving biological control. Also, sublethal concentrations of chlorantraniliprole could be leveraged to optimize T. japonicum mass rearing and augmentative release within IPM programs.