Plant Successional Stage and Insect Herbivory: Flea Beetles on Sand‐Dune Willow

The effects of early plant successional stage on the abundance and amounts of damage caused by a specialist herbivore were investigated for sand—dune willow, Salix cordata (Salicaceae), growing on sand dunes of varying ages. Both adults and larvae of Altica subplicata (Coleoptera: Chrysomelidae) were very abundant on host plants growing on the youngest and intermediate—aged dunes, but were absent from most plants growing on the oldest dunes. Amounts of beetle damage were greatest on the youngest dune, with nearly half of the plants having no leaves at the end of the season, and damage decreased with increasing successional stage. To explain these patterns of herbivory, laboratory and field studies we used to examine beetle survivorship, feeding preferences, and movement patterns. There was no difference in larval survivorship or growth rate as a function of the age of the community in which host plants were growing. Plant successional stage also did not influence larval feeding preferences, however, adults preferred leaves from the oldest dunes. Mark—recapture experiments revealed significantly longer residence times for beetles released in younger successional areas than in older successional areas, indicating that beetle movement behavior was consistent with patterns of abundance on dunes of varying ages. Several hypotheses were tested to determine whether beetle abundances were influenced by other factors that vary with successional stage, including host plant attributes (host plant height and nutritional quality) and attributes of the plant community surrounding host plants (abundance of surrounding nonhost neighbors and proximity to neighboring host plants). The increase in host plant height with succession was not responsible for the absence of beetles on older dunes, since taller plants on the younger dunes supported even higher beetle abundance than did shorter plants. Leaf nitrogen content decreased with succession and was consistent with patterns of beetle abundance. Although plant successional stage influenced numbers of neighboring host plants as well as herbaceous dicots and woody plants, differences between numbers of beetles on dunes varying in successional stage were not caused by the composition of the surrounding plant community. These results suggest that patterns of herbivore abundance were most strongly affected by movement patterns and host plant quality, and that effects of successional stage on herbivory are an important influence on herbivore—plant dynamics in successional systems.