Parasitism of a Hawaiian Endemic Moth by Invasive and Purposely Introduced Hymenoptera Species

Abstract

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.

Ecological correlates of the non-indigenous parasitoid assemblage associated with a Hawaiian endemic moth

“…This is confirmed by the results of the present study, and supports the idea that relative abundance of the host is of primary importance in determining parasitoid species richness (Price 1970;Sheehan 1994;Hawkins et al 1990;Mills 1992). Kaufman and Wright (2010), also suggested that host plant abundance had a direct influence on U. stellata density. Results of the PCA using environmental variables as primary data showed that host plant abundance was indeed positively correlated with U. stellata abundance, and this is likely a causal relationship.…”

“…In a previous study (Kaufman and Wright 2010), it was reported that sites with low abundance of U. stellata larvae also had fewer parasitoid species associated with U. stellata in those sites. This is confirmed by the results of the present study, and supports the idea that relative abundance of the host is of primary importance in determining parasitoid species richness (Price 1970;Sheehan 1994;Hawkins et al 1990;Mills 1992).…”

“…The observed differences among study sites may be the result of differences in ecological factors such as elevation, level of disturbance by alien plants, host plant density, density of insect host, and canopy cover. Results presented in previous studies have shown that adventive parasitoids, rather than purposely introduced ones, were responsible for the greater part of U. stellata mortality (Kaufman and Wright 2009b;Kaufman and Wright 2010). At low and low-medium elevations (between 240 and 900 m asl), the parasitoid assemblage was dominated by adventive species.…”

“…Previous work showed that the composition of the parasitoid assemblage and field parasitism rates by individual parasitoid species varied significantly among study sites (Kaufman and Wright 2010). The observed differences among study sites may be the result of differences in ecological factors such as elevation, level of disturbance by alien plants, host plant density, density of insect host, and canopy cover.…”

Local adaptation and ecological fitting in host use of theDrosophilaparasitoidLeptopilina japonica

“…Although the evolution of novel virulence mechanisms (i.e., adaptation) is the major process enabling parasitoids to use novel hosts, a number of parasitoids are known to parasitize unfamiliar host species, both in the laboratory and in the field (Cameron et al 2006;Kaufman and Wright 2010;Harvey et al 2012). In our previous studies, for example, we observed that some Leptopilina species from the Ryukyu Islands or Taiwan parasitize D. simulans Sturtevant, an exotic species seldom found in those regions (Novkovic´et al 2011(Novkovic´et al , 2012.…”