Cold tolerance of the predatory ladybird Cryptolaemus montrouzieri

The effect of low temperature acclimation and diet on the supercooling point (SCP, the temperature at which the insect’s body fluids freeze) and lethal time (LTime, time required to kill 50 % of the population at a temperature of 5 °C) of the mealybug destroyer, Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae), was assessed in the laboratory. The SCP of acclimated adult ladybirds which were allowed to complete development to adulthood at 18 °C and a 8:16(L:D)h photoperiod, or at 25 °C and a 16:8(L:D)h photoperiod, and which were subsequently kept at 10 °C and a 12:12(L:D)h photoperiod for seven days, was −17.4 and −16.8 °C, respectively. These SCP-values were approximately 7 °C lower than the value of −9.9 °C for non-acclimated ladybirds maintained at a temperature of 25 °C and a photoperiod of 16:8(L:D)h throughout development and in the first week of their adult life. Also food source had a significant effect on the freezing temperature of C. montrouzieri: the SCP of ladybirds fed the citrus mealybug, Planococcus citri (Risso)(Hemiptera: Pseudococcidae), was 1.6 °C higher than the value of −17.2 °C observed for ladybirds provided with eggs of the flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). However, neither cold acclimation nor diet had a significant effect on the lethal times of C. montrouzieri. Overall, the time required to kill 50 % of the population at a temperature of 5 °C ranged from 12.8 days for ladybirds fed P. citri mealybugs to 14.4 days for ladybirds fed E. kuehniella eggs. All individuals exposed to a constant 5 °C had died by day 24. Based on the results from this laboratory study, it is deemed unlikely that C. montrouzieri could establish outdoors in western Europe, and it is therefore expected to pose little risk to non-target species in this area when used as an augmentative biological control agent.