Freeze tolerance of a beneficial lady beetle, <i>Hippodamia convergens</i>

<jats:p> The convergent lady beetle <jats:italic>Hippodamia convergens</jats:italic> is widespread in the Americas and considered an important beneficial insect due to its use in pest control. Early work on this species characterized the beetles as freeze-avoidant (freeze-intolerant), suggesting they survive low winter temperatures by physiologically preventing ice formation to temperatures as low as -15°C. Here, we show that <jats:italic>H. convergens</jats:italic> can be freeze-tolerant if ice formation occurs at relatively high temperatures. There was 100% survival following inoculative freezing at -0.5°C and exposure to -3°C for 20 hours, as well as freezing that spontaneously occurred in fed beetles exposed to -4°C for 4 hours. Males exposed to 0°C or -4°C for 4 hours had similar mating behaviours (latency to first mating, copulation duration) as control beetles exposed to 4°C, although sample sizes were too small to determine whether freezing itself had an effect on these behaviours. Several putative cryoprotectants were detected in fat body tissue of <jats:italic>H. convergens</jats:italic> : glycerol, proline, trehalose, and <jats:italic>myo</jats:italic> -inositol — in order of abundance. Exposure to -3°C for 20 hours, whether frozen or unfrozen, did not statistically affect cryoprotectant accumulation, although there was a trend towards increased glycerol following freezing. This study is the first to describe inoculative freeze tolerance in a lady beetle and establishes a baseline for future studies that examine the mechanisms underlying this freeze tolerance and the effects of freezing on reproductive behaviour. </jats:p>