Effect of cold storage of Corcyra cephalonica eggs on the fitness for Trichogramma chilonis

Abstract

Cold storage of host eggs is important for Trichogramma mass rearing, but the fitness of Trichogramma is affected by the refrigerated eggs. Corcyra cephalonica eggs are frequently utilized as factitious hosts of Trichogramma chilonis. In this study, we investigated the physicochemical property of fresh rice moth eggs (U) and sterilized eggs cold-stored at 4 °C for 0 (CK), 15 (N15), 30 (N30), 45 (N45), and 60 (N60) days and evaluated the effect of cold storage of host eggs on the fitness of T. chilonis. The results showed that the moisture content, dry matter and pH of C. cephalonica eggs decreased significantly with increasing cold storage time. The survival rates of T. chilonis embryos, larvae and pupae decreased significantly when C. cephalonica eggs were cold-stored for more than 15 days. The fecundity rate of adult T. chilonis in refrigerated eggs declined markedly, and a similar result was observed in the rate of black parasitized eggs. However, no clear difference was observed in either emergence rate or sex ratio between the CK and N15 treatment. A fitted linear regression model revealed that the survival rates of immature T. chilonis were positively correlated to the moisture content and pH of host eggs. Thus, cold storage changed the internal environment of C. cephalonica eggs and reduced the fitness for T. chilonis. This finding suggests that the storage period of rice moth eggs sterilized by UV at 4 °C should not exceed 15 days for mass-rearing of T. chilonis.