Fitness effects of cold in the light brown apple moth (Epiphyas postvittana)

The light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), a leafroller native to southern Australia, continues to invade new areas of California and Oregon.  Epiphyas postvittana is highly polyphagous and threatens many agricultural and horticultural crops, with the potential to cause millions of dollars in damage annually.  Damage estimates are sensitive to the final national geographic distribution of this pest. Current predictions assume the insect will not establish in areas with temperatures below -16°C, but do not account for sublethal effects of cold exposure.  The potential for such effects could restrict the area of establishment or impact, but no prior studies have documented these effects in E. postvittana. We exposed late instars and pupae to cold temperatures and measured the direct and indirect effects of this exposure on subsequent survivorship, development, and reproduction.  Cold exposure included -10°C (a low but not immediately lethal temperature) and the supercooling point (the temperature at which internal fluids freeze).  Surviving insects were mated with untreated adults. We measured larval and pupal development time, pupal weight, adult longevity and fertility of treated females and mates of treated males. Nearly 20% of larvae and 8% of pupae were found to survive supercooling and continue development. Such survival following freezing suggests that E. postvittana has a mixed cold response of freeze tolerance and intolerance, in contrast to previous assessments that categorize it as only freeze intolerant. Importantly, our study also shows there may be a tradeoff between survival of cold and fitness in E. postvittana.