Parasitism of a Hawaiian endemic moth by invasive and purposely introduced Hymenoptera species.

The impact of invasive alien species on native organisms is a cause for serious concern. This concern is especially relevant in the Hawaiian archipelago because of its high level of endemicity, severe impacts of accidental introductions of invasive species, and long history of purposeful biological control introductions. Results from a previous study showed that the parasitoid assemblage associated with an endemic moth Udea stellata (Butler) comprised seven species: three adventive species, two purposely introduced species, and two of unknown origin. The objectives of this study were to assess the parasitism levels of alien wasps on populations of U. stellata at different sites and to determine the specific stages that were used by the spectrum of parasitoid species that attack U. stellata. Standardized collections of wild larvae were conducted at eight sites located on the islands of Kauai, Oahu, and Hawaii. In total, 3,531 larvae were collected in a 2-yr survey. Of these, 8.0% were collected as first instar, 23.0% as second instar, 39.0% as third instar, 21.0% as fourth instar, 7.1% as fifth instar, and 1.8% as sixth instar. Of the larvae that survived laboratory rearing, 43.0% were parasitized. Information collected in the surveys was complemented with data from life-table studies to determine stage-specific parasitism. All larval stages were susceptible to parasitism by at least one parasitoid species; second and third instars were susceptible to attack by all seven parasitoid species. Adventive parasitoids rather than purposely introduced ones were responsible for the greater part of the apparent mortality observed. At low and low-medium elevations, the parasitoid assemblage was dominated by adventive species. The two purposely introduced parasitoids were present in remote relatively undisturbed sites on the islands Kauai and Hawaii. The sometimes high parasitism rates by adventive species found in this study were shown to have minimal effect at the population level in our life table study; therefore, care should be taken when interpreting field parasitism data. Carefully addressing current ecological impacts of alien parasitoids on native species is of particular importance for developing more efficient means to quantify the risks of future biological control introductions.