PARENT SESSION
Oral Session # 73: Invasive Species VI: Terrestrial.
Presiding: S DeWalt
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 204.
Vanishing native parasitoids: Competitive exclusion by an exotic biological control agent?
Parry, Dylan *,1, Boettner, George2, 1 State University of New York, Syracuse, NY, USA2 University of Massachusetts, Amherst, MA, USA
ABSTRACT- The non-target effects of parasitoids released for biological control have increasingly drawn attention from ecologists. A classic case is that of Compsilura concinnata, a tachinid fly introduced to control gypsy moth in 1907. This old world species is now known to attack >200 species of native Lepidoptera in North America and has been implicated in the decline of several species of giant silk moth. The effect of C. concinnata on native parasitoids is not known, even though it is often the only species reared from several different native hosts in New England. To investigate whether C. concinnata has displaced native parasitoids, we focused on the North American analog of C. concinnata, the highly polyphagous tachinid Lespesia frenchii. Our study was conducted in areas of New England where comprehensive data on parasitoid diversity was collected for more than 100 native Lepidoptera shortly (1915-1929) after the release of C. concinnata. This enabled us to compare present day parasitoid diversity with historical data from the same region. We utilized two complimentary approaches. First, we deployed experimental populations of several forest lepidopteran hosts and retrieved sentinel larvae to assess parasitism and species diversity. Secondly, we quantified the presence or absence of L. frenchii in 15 museum collections from 1920-2000 in three states where the initial arrival of C. concinnata was well documented. We did not recover L. frenchii from any experimentally reared or wild collected host species in New England, including those where L. frenchii was the dominant parasitoid prior to 1930. Museum collection data corroborated the results from our field studies. The rate at which L. frenchii acquisitions were added to entomological collections dropped sharply after the introduction of C. concinnata. Although the mechanism that allows C. concinnata to be competitively superior is unclear, both interference and exploitative competition are likely.
Key words: invasive, Compsilura, non-target, competition