The effect of red wood ant abundance on feeding damage by the pine weevil Hylobius abietis

摘要

Red wood ants (Formica rufa group) are the dominant ant species in European forests that can affect the abundance of other arthropods (e.g. herbivorous insects in tree canopies or beetles on the forest floor). Notably, ants can prevent pine weevils (Hylobius abietis) from feeding on conifer seedlings supplied with food sources for ants. This is a potentially important observation because the weevil is a serious pest in forest regeneration areas. We hypothesized that frequent encounters between red wood ants and pine weevils on the ground may decrease the weevils' feeding on conifer seedlings. To test this hypothesis, we compared feeding damage caused by pine weevils on spruce seedlings in areas with high and low abundance of red wood ants. Despite a four-fold difference in the numbers of ants in pitfall trap samples, there were no significant differences between areas with high and low ant abundance in terms of feeding-scar areas, proportions of attacked seedlings or proportions of killed seedlings. Thus, in contrast to previously documented deterrent effects on ground-dwelling beetles, high abundance of ants on the ground did not influence the feeding activity of pine weevils on the spruce seedlings. We conclude that the mechanisms underlying seedling protection by ants are probably mainly related to the ants' protection of food sources, whereas the frequency of encounters elsewhere has less effect on the weevils' feeding.