Optimizing diapause and storage parameters for mass rearing of Trichogramma japonicum

Trichogramma japonicum Ashmead is a key egg parasitoid used in the biological control of lepidopteran pests, notably in rice fields.To improve its mass rearing and field application, this study explored the combined effects of diapause induction and storage conditions on its emergence rate, using Corcyra cephalonica eggs as intermediate hosts.We investigated the impact of initial induction stage, induction temperature and duration, storage temperature, and storage duration.Results showed that emergence rates were significantly influenced by all tested factors.Storage at 4 C consistently yielded the highest emergence rates.Emergence increased with storage duration, peaking around 60 days before declining.Maternal exposure to a short photoperiod (8L:16D) notably improved emergence, and a 24-hour post-parasitism induction stage resulted in higher rates than a 48-hour stage.Induction temperature also played a critical role, with 13 C proving more effective than other temperatures.Additionally, longer induction durations increased emergence, with 35 days being the most favorable.The optimal conditions identified were: maternal short photoperiod exposure (8L:16D), diapause induction at 13 C for 35 days following 24 hours of post-parasitism development, and storage at 4 C for 60-90 days.Under these parameters, emergence rates exceeded 90%.This study provides a comprehensive basis for optimizing the industrial-scale production and storage of diapaused T. japonicum, enhancing its reliability and application in integrated pest management (IPM) strategies.