Long-term cold response in overwintering adults of ladybird Hippodamia variegata (Coleoptera: Coccinellidae)

Hippodamia variegata is an efficient and most abundant predatory coccinellid in many countries. Understanding the ability of long-term low temperature survival in beneficial insects can be used to make better predictions about subsequent abundance and hence the biological control potential in the next spring and summer. So in this study, effects of long-term low temperatures were investigated on mortality and supercooling point (SCP) of field collected (pre-diapausing) and overwintering aggregations of H. variegata adults. Unlike the pre-diapausing insects, aggregated coccinellids could easily survive at -3 and 0 °C for one month. One month acclimation at 10 °C caused more than 80% mortality in overwintering adults, indicating that higher temperatures were not appropriate for overwintering aggregated coccinellid. In December and January, when diapause was in its highest level, changing the habitat temperature did not affect SCP. Acclimatization at 5 and 0 °C for one month decreased SCP of pre-diapausing adults, collected from aphid infested plants in October. Our study revealed that long term exposure to temperatures below 0 °C that usually happen in natural conditions may be necessary for overwintering of the coccinellid.