Extra Food Supply Decreases Damage by the Pine Weevil Hylobius abietis

Abstract

It has been suggested that reduced damage by the pine weevil ( Hylobius abietis ) under shelter trees might result from more food being available under shelter trees than on clear-cuttings. The shelter trees provide an extra supply of bark on branches and roots. Moreover, shelter trees favour some species in the ground vegetation (e.g. bilberry, Vaccinium myrtillus ) that could be used as food by the weevil. Two similarly designed field experiments, studied whether the amount of pine weevil feeding on planted conifer seedlings was affected by the availability of other food sources. In the first experiment, fresh pine branches were placed weekly on the ground for 6 weeks on a fresh clear-cutting in southern Sweden. This significantly reduced the amount of feeding on seedlings in treated 20 2 20 m plots. In the second experiment, damage tended to increase after mechanical removal of field vegetation (mainly bilberry), but the effect was not statistically significant. In conclusion, extra food in the form of coniferous bark could relieve seedlings from pine weevil damage; however, any effect of this kind due to the presence of field-layer vegetation remains to be demonstrated. Finally, there may be long-term population effects because of the extra food that the shelter trees provide for the reproductive weevils.