The effects of simulated acid rain on growth and susceptibility to predation of Phratora polaris (Col., Chrysomelidae)

Abstract

The effects of long-term simulated acid rain on tritrophic interactions between mountain birch, a leaf beetle ( Phratora polaris) and its predators were studied. Leaf beetle larvae were fed on foliage treated during 6–7 years with simulated acid rain of pH 3 (both H 2S0 4 and HNO 3) or with spring water of pH 6 (irrigated controls). There were significant differences between treatments in the susceptibility of P. polaris to predators. Generally, beetles reared on acid treated birches were more susceptible to predators than those reared on irrigated control trees. This effect was present over several stages in the life cycle of the beetle and for several types of predators: ants preying on larvae, carabids attacking pupae and birds feeding on adult beetles. However, host plant treatment did not have consistent effects on the growth of larvae. This suggests that the defensive ability of leaf beetles is more sensitive to pollution induced variation in host foliage than larval growth.