Selection of hibernation sites by Anthonomus pomorum: preferences and ecological consequences

The apple blossom weevil, Anthonomus pomorum (L.) (Coleoptera: Curculionida e), has a long period of aestivo-hibernation in the adult stage lasting fro m summer to early spring of the following year. Potential hibernation sites within an apple orchard consist of high-stem rough-bark trees or dwarf smo oth-bark trees. Field release-recapture experiments in 2 consecutive years showed that 64 and 47% of the weevils remained in the vicinity of the relea se sites in an area of high-stem trees and dwarf trees, respectively. The d ispersing weevils moved over an average distance of 5.5 m in the dwarf tree area, as compared to 3.8 m in the high-stem tree area. The prevalent direc tion of dispersal was along tree rows in both areas. Some weevils displayed , after release in mid-July, a directional dispersal to the adjacent forest s. Others, released in the dwarf tree area, dispersed towards the area of h igh-stem rough-bark apple trees. Experiments simulating various hibernation sites demonstrated that the litter of dry leaves was the most preferred ov erwintering shelter, yielding a relatively high survival rate. Branches wit h rough bark ranked second, while branches with smooth bark, grass and pure soil were not favourable for overwintering. Flight tendency in newly emerg ed weevils of summer generation was significantly higher in June/July than in August/September. This corresponds to the dispersal behaviour in the fie ld. The timing of spring colonisation of apple trees was similar for weevil s overwintering within the orchard and for those from outside. These result s suggest that modern, dwarf apple orchards offer unfavourable conditions f or overwintering, but that the relatively small proportion of weevils which manage to reach the adjacent forests find optimal hibernation sites there.