The effect of temperature on the development and life cycle regulation of the pine weevil Hylobius abietis and the potential impacts of climate change

1 The pine weevil Hylobius abietis is widely distributed in the Palaearctic region where it is a major pest. Although predominantly semi-voltine, with a 2-year life cycle, the generation time across its range can vary from 1 to 4 years. The duration of the life cycle and the seasonal timing of weevil activity affect the economic impact and management of this pest, all of which are likely to change in a warming climate. 2 To determine the effect of temperature and tree species on weevil growth and development, laboratory experiments were performed with eggs, larvae, prepupae, pupae and adults, using, as appropriate, the host species Scots pine Pinus sylvestris L. and Sitka spruce Picea sitchensis (Bong.) Carr. under constant or alternating temperatures. 3 The development rate was linearly related to temperature, with developmental thresholds for eggs, larvae and pupae of 8, 4.5 and 7.3 degrees C, respectively. Day-degrees were estimated for each life stage. Larval development was affected by tree species, being slower on Sitka spruce than on Scots pine, and was faster under alternating than constant temperatures. 4 The development time for prepupae was highly variable, with an apparent facultative prepupal diapause initiated by temperature. The temperature range 2017.5 degrees C marked the transition between median prepupal development times of approximately 25 and 90 days. The prepupal stage may serve to minimize the risk of overwintering mortality in the pupal stage and help to synchronize the life cycle. 5 Larval and adult mass was positively related to developmental temperature, demonstrating an inverse temperature size rule, and weevils were heavier when developing on Scots pine than Sitka spruce. Development in alternating temperatures reduced weevil mass on Scots pine. The influence of temperature on weevil mass is likely to have a positive effect on fecundity and overwintering survival. The effects of climate change on development, voltinism and weevil mass are discussed.