Interestingly, phenolic levels in these species were consistently lower in the drier 1993 summer and the differences in phenolic concentrations between understory and mature trees of each species were less pronounced than in 1992. These results showed clear reductions in plant allocation to foliar nutrients and phenolic defenses during drought and indicate the likely direction of foliar chemical changes that can be expected as the Throughfall Displacement Experiment progresses. The reduced feeding from white oak and chestnut oak trees in 1993 may have occurred in response to the poorer nutritive quality of oak leaves during the drier summer. Feeding by leaf skeletonizers was much less in 1993 than 1992 and accounted for nearly all of the reduction in leaf damage on both oak species. In contrast, herbivore damage on red maple trees was identical both years.
Maple trees experience very little feeding by skeletonizers.
Therefore, the decline in importance of this insect feeding guild in 1993 would have no impact on total leaf area damaged on maple. Our results thus suggest a guild specific response to drought among insect herbivores which may be related to the changes in nutritive quality of oak leaves as moisture becomes limiting. Continuation of the Throughfall Displacement Experiment should enable us to further examine the response of particular insect feeding guilds to moisture induced changes in plant nutrients and phenolic defenses. Effects of rainfall modification on plant-herbivore processes, Oak Ridge Conf.