Does forest tent caterpillar feeding affect gypsy moth susceptibility to its nucleopolyhedrosis virus?

The invasive gypsy moth (Lymantria dispar L.) has broad potential to affect native North American forest insects, especially communities of caterpillars with which it shares hosts and natural enemies. Earlier research on the impacts of the gypsy moth on native Lepidoptera has shown a strong positive association between the invasive species and the forest tent caterpillar (Malacosoma disstria Hübner), a spring defoliator that phenologically precedes the gypsy moth in Canada. Previous work has suggested that changes in host plant chemistry can alter the gypsy moth's susceptibility to its nucleopolyhedrosis virus, either positively or negatively depending on the host tree. Our study investigates the hypothesis that feeding by the forest tent caterpillar can induce changes in host plant chemistry that indirectly affect gypsy moth growth and mortality. Red oak (Quercus rubra) and trembling aspen (Populus tremuloides) trees were subjected to one of four treatments: control; control + virus; forest tent caterpillar; and, forest tent caterpillar + virus. Gypsy moth survival and pupal weights were assessed, as were levels of relevant leaf phenolics. The results of this study demonstrate the complexity of interactions between exotic and native species following invasion.