Invasive insects are considered one of the most serious threats affecting forests today; however, surprisingly little research has addressed the impacts of invasive species establishment on native forest insect communities. Such information is lacking for even the most thoroughly studied invasive forest insect, the gypsy moth. Using gypsy moth as a case study, my thesis addresses the questions: What are the ecological impacts of an exotic forest insect upon its establishment in a new community of native species? Does the community shift after the invasive establishes, and if so, what are the drivers in this realignment? I used multivariate analysis to assess native caterpillar communities collected in forest stands with and without a history of gypsy moth outbreak. I found that gypsy moth outbreak history had no significant effects on native caterpillar communities; however, current gypsy moth abundance was related to shifts in the structure of late season caterpillar assemblages. These results suggest that gypsy moth may affect native caterpillar communities through short-term mechanisms but not through long-term ecological changes. I used quantitative food webs to investigate the effects of gypsy moth on native host-parasitoid webs from the same caterpillar communities, and found that food web structure was resilient to both gypsy moth outbreak history and current abundance. The gypsy moth shared few parasitoids with native species in my study sites, none of numerical significance, thus minimizing the opportunity for enemy-mediated indirect interactions. Finally, I conducted a greenhouse experiment and found that early spring feeding by forest tent caterpillar can indirectly influence gypsy moth susceptibility to its virus, demonstrating that the complex interactions that can occur between native and exotic species do not always benefit the invader. Overall, I argue that the establishment of the gypsy moth into North American forests will not cause major changes in native caterpillar communities.

Invasive insects are considered one of the most serious threats affecting forests today; however, surprisingly little research has addressed the impacts of invasive species establishment on native forest insect communities. Such information is lacking for even the most thoroughly studied invasive forest insect, the gypsy moth. Using gypsy moth as a case study, my thesis addresses the questions: What are the ecological impacts of an exotic forest insect upon its establishment in a new community of native species? Does the community shift after the invasive establishes, and if so, what are the drivers in this realignment? I used multivariate analysis to assess native caterpillar communities collected in forest stands with and without a history of gypsy moth outbreak. I found that gypsy moth outbreak history had no significant effects on native caterpillar communities; however, current gypsy moth abundance was related to shifts in the structure of late season caterpillar assemblages. These results suggest that gypsy moth may affect native caterpillar communities through short-term mechanisms but not through long-term ecological changes. I used quantitative food webs to investigate the effects of gypsy moth on native host-parasitoid webs from the same caterpillar communities, and found that food web structure was resilient to both gypsy moth outbreak history and current abundance. The gypsy moth shared few parasitoids with native species in my study sites, none of numerical significance, thus minimizing the opportunity for enemy-mediated indirect interactions. Finally, I conducted a greenhouse experiment and found that early spring feeding by forest tent caterpillar can indirectly influence gypsy moth susceptibility to its virus, demonstrating that the complex interactions that can occur between native and exotic species do not always benefit the invader. Overall, I argue that the establishment of the gypsy moth into North American forests will not cause major changes in native caterpillar communities.