SYNCHRONIZATION OF HATCHING DATE WITH BUDBURST OF INDIVIDUAL HOST TREES (QUERCUS-ROBUR) IN THE WINTER MOTH (OPEROPHTERA-BRUMATA) AND ITS FITNESS CONSEQUENCES

1. Due to varying selection pressures among host individuals, herbivor ous insects may show local adaptation at the individual level. In the winter moth, synchrony of egg hatching and host tree (Quercus robur L. ) budburst may have important fitness consequences and, therefore, may result in a local adaptation to the hosts phenology. However, relativ ely high gene how levers may disrupt such a fine-scale adaption. 2. We determined hatching dates of clutches laid by females collected durin g copulation, and variation in budburst dates of the trees on which th ese couples were collected. 3. In our study area, budburst date showed substantial variation within years and areas, as the first and last t ree to start leafing were separated by up to 26 days. Relative budburs t dates of individual trees were constant between years. Average hatch ing dates differed significantly among clutches and varied over 30 day s, a range comparable to that of budburst. 4. Hatching dates were posi tively associated with budburst of the respective trees indicating ind ividual synchrony, which may be mediated by two mechanisms. First, ear ly active adults are captured more frequently on early trees and late adults on late trees. As adult activity period is positively correlate d with date of egg hatch, early clutches will tend to be laid on earli er trees while late clutches will be laid more frequently on late tree s. Secondly, a presumed active choice mechanism may additionally incre ases individual host synchronization. Yet, the latter requires further study. 5. Our data support that synchronization of larval hatching wi th host budburst is adaptive as it increases adult size and thus expec ted fitness.