Associations of Plants and Insects in Deciduous Forest

Phytophagous insect larvae (Lepidoptera and Tenthredinoidea) in the leaf—chewing guild were sampled from accessible parts of all the 18 species of common woody plants in a mature upland forest in New York State, in early and in late June. Among the procedures used to describe patterns of associations between plants and insects are principal components analysis and the clustering techniques of numerical taxonomy, whereby the faunistic similarity among plant species is described. We introduce a weighting factor for cluster analysis that weights a character (in this case the density of an insect species on a plant) in proportion to its deviation from the norm. During June, both the abundance and variety of insects declined on most plant species, which vary greatly in both these aspects of their fauna. Insect species that are either quite highly specialized or generalized in diet appeared to be prevalent; those with intermediate diet breadth were less so. Clustering plant species by faunal similarity revealed some clusters of taxonomically related species, but the correspondence between faunal similarity and taxonomic affinity is not strong. Few plant species have a highly distinct, specialized fauna. The complexity of distribution of insects over plants indicates that insects are responding to many factors that differentiate plant species.