Leaf pubescence affects distribution and abundance of generalist slug caterpillars (Lepidoptera: Limacodidae)

Insect herbivores often respond to leaf texture in making oviposition or feeding choices. This study examined the importance of leaf pubescence for an assemblage of generalist caterpillars (Lepidoptera: Limacodidae) feeding on oaks (Quercus spp.) and a variety of other tree species in eastern North America. Based on 10 yr of larval sampling on canopy and understory black and white oak (Quercus velutina and Q. alba, respectively) in the Ozark Mountains of Missouri, larval density of slug caterpillars (14 species as a group and 3 individual species) was higher on glabrous canopy leaves of Q. velutina than on highly pubescent understory leaves of that species. In contrast, there was no effect of stratum on overall density for Q. alba, which has glabrous leaves in both microenvironments. Individually, stratum effects for Q. alba were significant for five species, four of which were more abundant in the understory. Additional censusing of larvae on 20 tree species varying in leaf pubescence found that, as a group, slug caterpillar density was negatively correlated with leaf hair density. Finally, feeding trials confirmed that slug caterpillars prefer canopy over understory leaves of Q. velutina and vice versa for Q. alba leaves. When hairs were experimentally removed from one side of Q. velutina understory leaves, caterpillars preferred the side from which hairs were removed over the intact side. Together, these results indicate that leaf pubescence influences patterns of host plant use by these generalist herbivores, and in so doing, contributes to the structuring of local herbivore communities.