Effect of long-term cold storage on the fitness of pre-wintering Harmonia axyridis (Pallas)

The multicolored Asian ladybird beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), is considered an important generalist predator that can be used as a biological control agent against Hemiptera Sternorrhyncha, Thysanoptera, and the eggs and larvae of Lepidoptera, Coleoptera and Diptera. There are currently abundant natural resources of overwintering H. axyridis in Asia and North America. Given its potential as a biological control agent, methods can be developed to increase its effectiveness for pest control. The availability of an adequate cold storage method would enable the use of field-collected pre-wintering ladybirds for pest suppression in the following season. We studied the effect of cold storage (30, 60, 90, 120 and 150 days stored at −3, 0, 3 and 6°C) on survival, fecundity and predation in field-collected populations. The survival of both female and male ladybirds decreased significantly as storage duration increased at −3°C and 0°C. The ladybirds showed more than 80% survival when they were stored for 150 days at 3°C and 6°C. Long-term cold storage had different effects on the fecundity of H. axyridis at different temperatures. Prolonged cold storage at both 3°C and 6°C shortened pre-oviposition duration and had no adverse effect on reproductive capacity as compared to that of unstored individuals. The adults that experienced 90-day storage at 0°C had the shortest pre-oviposition duration and the largest reproductive capacity. The individuals that were stored for 150 days at 3°C consumed significantly more aphids than the unstored ones. Generally, 3–6°C is a suitable temperature for cold storage of the ladybird without any reduction in fitness. This study will help the exploitation and application of pre-wintering H. axyridis for the biological control of insect pests.