Flight ability and reproductive development in newly-emerged pine weevil Hylobius abietis and the potential effects of climate change

1 Adult pine weevils Hylobius abietis emerge from conifer root-stumps, on which larvae develop, over an extended period during summer and autumn. Newly-emerged weevils were tested for their ability to fly and assessed for wing muscle and reproductive development. In addition, the effect of summer-autumn maturation feeding on reproductive development was assessed in field bioassays. 2 There was considerable variation in development between newly-emerged weevils that was related to the timing of emergence. The first weevils, emerging in early July, weighed less than later-emerging ones, had undeveloped flight muscles and did not fly. Over the emergence period, wing muscle size and flight ability increased markedly, with 50-60% flying by mid-September. Differences between emerging adults are likely to have been affected by temporal changes in the quality of the bark on which the larvae feed. 3 Reproductive development lagged behind that of wing muscles but, in early August, there was a rapid increase in the proportion of weevils with immature eggs and a corresponding increase in oocyte size. However, although wing muscles were fully formed in later-emerging weevils, immature eggs were only approximately 10% of the volume of mature eggs. 4 In field bioassays of summer-autumn maturation feeding, eggs continued to develop and some weevils laid mature eggs. Feeding and development during the pre-overwinter period is likely to influence winter survival and also dispersal and reproduction in the following spring. 5 The potential effects of climate change on the weevil life cycle are briefly discussed. Weevils are likely to benefit from the higher temperatures and later autumns predicted under climate change, resulting in an increase in damage to transplants.