Abstract BACKGROUND The rice moth, Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) is a pest of stored grains and widely used as a factitious host during the mass rearing of several natural enemies of crop pests. Hormesis is well‐documented in pest insects, to some extent in natural enemies of pests. RESULTS We report transgenerational stimulatory effects of the widely used fumigant, phosphine. The study reports the consequences of sublethal, low lethal and median lethal concentrations (LC 5 , LC 25 and LC 50 ) and untreated control for two sequential generations of the species (G 1 to G 2 ). In this study, we investigated the life‐history traits, nutrient reserves (protein, lipid and carbohydrate) and larval gut microbiome (using 16 s rRNA V3–V4 metagenomics sequencing) of C. cephalonica . Stimulatory effects were observed for various biological traits of C. cephalonica , notably adult longevity, emergence and increased egg hatchability when exposed to LC 5 of phosphine. The total protein, lipid and carbohydrate contents of C. cephalonica also were found to be significantly increased by LC 5 in both generations. The microbial diversity of LC 5 treated larval gut was higher and found to be different from the rest of the treatments. This is the first report showing hormesis to a fumigant insecticide. CONCLUSION Our findings increase knowledge on the interaction between hormesis, nutrient reserves and gut bacteria in C. cephalonica exposed to insecticides. Overall, the present study establishes phosphine‐induced hormesis at LC 5 in the host C. cephalonica , which might help improve the quality of mass rearing of various natural enemies. © 2023 Society of Chemical Industry.