ABSTRACT
Forest insects shape and change their environment in various ways. Tunnels of wood-boring beetles, for instance, become habitats for wild bees. At a larger scale, defoliation by herbivores changes the stand climate, which in turn affects the ground vegetation. Bark beetles can kill entire tree stands, thereby creating deadwood and open habitats for organisms. This initiates a new forest succession.
Another so-called ‘ecosystem engineer’ is the larch bud moth. In the European Alps its univoltine populations go through regular cycles of 8 to 10 years with complete stand defoliation in the culmination years. Several mechanisms drive these cycles. Antagonists were found to be a prime driver of this moth's population dynamics. Interactions between larval feeding and the quality and availability of needles also play a major role. Moreover, caterpillar ecotypes with different degrees of fitness rotate cyclically. Large numbers of moths regularly drift across the alpine valleys, which helps to stabilise the cycles.
Only a small fraction of larch trees die after the defoliation. Swiss stone pines, however, which the budmoth also feeds on, do not tolerate extensive needle feeding. This prevents a shift from larch to stone-pine forests.
