Insect-Plant Patterns and Relationships in the Stem-Boring Guild

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Abstract
The relationships between insect and plant diversity were examined by determining the specific plant exploitation patterns of a guild of 48 stem-boring insects and by comparing the insect and plant patterns of dominance-diversity, species area and dispersion. The guild was sampled in two diverse tall grass prairie sites in Illinois [USA]. The shapes of the dominance-diversity and species-area curves were strikingly similar between the insects and plants, but the correlations proved to be superficial. The large number of rare stem-boring species did not reflect the number of rare resources because they exploited common stems. The numerical dominance of the guild could not be consistently related to either plant abundance or resource specialization. The common stem-borers were mostly oligophagous (exploiting several plant species), and they showed similar relative abundance rankings between the 2 sites despite some significant differences in their host plant abundance composition. The percent stem exploitation by the stem-borers was uncorrelated with the density of host plant stems. The simple abundance of stems proved to be a poor indicator of resource availability because most stem-borers preferred large stems, an aspect of plant structure. Some structurally favorable plant species were avoided while other small stems were exploited and the relationships varied from species to species. These results show that the determinants of insect diversity are specific and complex and that differences in either plant species, abundance or structure will have unpredictable influences on insect diversity. Contrary to most inferences from animal-plant diversity correlations, neither plant resource diversity nor competition can adequately account for the patterns of abundance, dispersion or exploitation shown by this herbivore guild, even though the patterns appear to be closely related.