Short-term effects of defoliation by gypsy moth larvae on Appalachian headwater streams in Virginia

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Virginia Tech


This field study investigated the short-term effects of riparian defoliation by gypsy moth larvae on three aspects of headwater stream ecology, water quality, benthic macroinvertebrate community structure, and benthic macroinvertebrate function (expressed as secondary production). The experimental design was to compare measurements in three streams that were extensively defoliated by gypsy moth larvae (defoliated treatment), with three streams that were not affected by gypsy moth larvae (reference treatment). Although the riparian canopy became much more open after defoliation, I observed no significant differences in any water quality parameters except temperature, which was slightly elevated for a brief period after defoliation. There was a significant increase in the amount of detritus (frass and orts) falling into defoliated streams in the spring, which was followed by a significant decrease in the of amount detritus falling into defoliated streams in autumn. Many measures of community structure were analyzed, but only the Index of Biotic Similarity demonstrated a significant difference, indicating that, at most, only slight changes in community structure occurred. Secondary production of two representative aquatic insects, Peltoperlidae (shredder) and Diplectrona modesta (collectorfilterer), was not affected by defoliation. Glossosoma nigrior (scraper) achieved higher production because of a second-generation being induced by elevated temperature. I conclude that the short-term effects of riparian defoliation by gypsy moth larvae were minor.