RESPONSES OF NATURAL ENEMIES TO EXPERIMENTALLY INCREASED POPULATIONS OF THE FOREST TENT CATERPILLAR, MALACOSOMA-DISSTRIA

1. The responses of predators and parasitoids to increased forest tent caterpillar populations were studied by introducing eggs to two tremb ling aspen, Populus tremuloides Michx., forests where natural populati ons were at very low density. 2. Of five parasitoid species recovered, only the braconid Aleiodes malacosomatos (Mason) and the tachinid Pat elloa pachypyga (Aldrich & Webber) exhibited spatially density-depende nt responses, in dry upland forest and mesic lowland forest, respectiv ely. Forest type restrictions on the abundance of these species and th e weak density-dependent response by A. malacosomatos suggests that pa rasitoids may not be capable of regulating low-density tent caterpilla r populations. 3. Predation of final-instar larvae and pupae by birds, in particular the northern oriole, Icterus galbula (L.), virtually el iminated the experimental populations. Avian predation was widespread and dominated mortality at all densities. 4. Implications for the init iation of outbreaks of cyclic defoliators are discussed.