Effects of gypsy-moth defoliation and Bacillus thuringiensis var. kurstaki treatments on native forest moth diversity and abundance

Background/Question/Methods

Since its introduction to North America, the gypsy moth (Lymantria dispar L.) has become a major defoliator of Eastern hardwood forests.  While there has long been interest in understanding the impact of these defoliation events on native arthropods, research has met with limited success due to the unpredictability of gypsy moth outbreaks. Shenandoah National Park (SNP) experienced major defoliation in June 2008, and some defoliated areas were treated with the Lepidopteran-specific insecticide Bacillus thuringiensis var. kurstaki (Btk) in May of the same year. In this study, long-term impacts of gypsy moth defoliation and Btk on native moths were evaluated in Summer 2011 by comparing moth diversity and abundance among sites in SNP experiencing Btk application and defoliation (Btk sites), defoliation but not Btk application (defoliated sites), and regions that have not experienced defoliation since 1995 (undisturbed sites). Fifteen sites – five of each site history type – were selected across a 30-km range.  Black-light trapping was conducted every four weeks (May – September) during optimal trapping conditions.  Specimens were identified to species and assigned a classification based on host plant preferences as either competitors of the gypsy moth, non-competitors, or capable of switching between gypsy moth-palatable or non-palatable plants.

Results/Conclusions

No significant differences in moth abundances among site histories were found, nor were there detectable differences in abundance among the site history types for the three most abundant families or for moth host plant classes.  Analyses of diversity revealed no effects of site history on local (α) diversity of the overall moth community or diversity of moths among sites (β-diversity).  There were also no significant differences in the α- or β-diversity of moth families or host-plant classes among site histories with one exception.  Geometridae α-diversity in late summer was significantly lower in untreated defoliated sites than in Btk sites or undisturbed sites.  This suggests gypsy moth defoliation has negative effects on moth diversity, but the majority of families have largely recovered in the time between the events and sampling.  This research builds on our understanding of the long-term impacts of an invasive defoliator on forest communities.