Optimizing cold storage of Sitotroga cerealella eggs for the mass rearing of Trichogrammatoidea bactrae: Effects on reproductive performance of parent and progeny.

Improving effective cold storage techniques for maintaining factitious host eggs without adversely affecting their quality and the performance of emerged parasitoids is essential. Therefore, this study investigated the effects of different storage temperatures (-2 °C, 2 °C, 4 °C, and 8 °C) and durations (1-25 days) on the quality of Sitotroga cerealella Olivier (Lepidoptera: Gelechiidae) eggs and the reproductive performance of both parents and offspring of Trichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae). This parasitoid demonstrated the ability to parasitize cold-stored eggs, albeit at varying rates influenced by temperature and storage duration. Storage at 4 °C sustained egg quality and parasitoid performance for up to 25 days, however, optimal results of high parasitism rates (> 93%), adult emergence (> 96%), and female proportions (> 75%) were specifically maintained for 19 days. Additionally, storage at 2 °C held host suitability for 13 days. These trends were consistent for both parental and progeny generations. In contrast, eggs stored at 8 °C, exhibited parasitism rates of approximately 85% for 9 days, dropping to 54% by day 17 and failing completely by day 19. Conversely, storage at - 2 °C caused rapid deterioration of host egg quality after 5 days, reducing parasitism (83.47%) and significantly reducing parental (F0) performance. However, parasitoids that successfully emerged did not exhibit detectable carry-over effects in the subsequent generation (F1). Notably, while parasitism rates declined at - 2 °C and 8 °C with extended storage, adult emergence remained consistently high (approximately 92-98%) across all durations. Under these storage conditions, parasitoid emergence was predominately female-biased (65-80%) in both generations. However, at - 2 °C after 9 days, the ratio shifted sharply to male-biased (52%) in F0 generation only, indicating an adverse effect on sex allocation, with no transgenerational effect in the F1 progeny. These findings identify 4 °C for 19 days as the optimal protocol for sustaining S. cerealella egg quality and T. bactrae efficacy, followed by 2 °C for 13 days. Selecting appropriate storage conditions is valuable for effective augmentative biological control programs.