Threats Posed to Rare or Endangered Insects by Invasions of Nonnative Species

Endangerment factors are reviewed for 57 U.S. federally listed insects and 116 rare eastern North American lepidopterans to determine the importance of invasive species relative to 15 other recognized endangerment factors. Invasive plants, social insects (especially ants), and vertebrate grazers and predators repeatedly were identified as groups directly or indirectly threatening native insect biodiversity. Among rare eastern North American lepidopterans, the (mostly indirect) consequences of the establishment of the gypsy moth (Lymantria dispar) surfaced as a general threat. Remote islands, especially those with high human visitation, stand out as being highly threatened by invasives. In the worst cases, impacts from invasive species cascade through a community and destabilize existing trophic interconnections and alter basic ecosystem properties, changing hydrology, nutrient cycles, soil chemistry, fire susceptibility, and light availability, and precipitate myriad other changes in biotic and abiotic parameters. Invasive ants and herbivorous insects provide some of the most dramatic examples of such insect-induced invasional cascades.