Distribution and abundance of larval parasitoids of European corn borer (Lepidoptera: Pyralidae) in the East Central United States.
Overwintering 5th-instar larvae of Ostrinia nubilalis were systematically collected at 621 sample sites on a grid interval of 40 km encompassing New York, Pennsylvania, Ohio, Delaware, Maryland, Virginia, West Virginia and North Carolina and were evaluated for parasitoids. The study was focused on the extent of dispersal of Lydella thompsoni from its presumed reestablishment in Delaware during the mid-1970s and the level of parasitism of overwintering O. nubilalis larvae. The bulk of the study was conducted in 1986 and 1987 with some additional samples taken in 1988 and 1989 from outlying locations. L. thompsoni, Macrocentrus grandii and Eriborus terebrans [Diadegma terebrans] were the only exotic species recovered. All 3 of these parasitoids were found in all states surveyed. Parasitism by these 3 species combined was 5.4% in 1986 and 7.5% in 1987 for the entire areas surveyed. The areas of most abundance for each species were in North Carolina for L. thompsoni, a band from northeastern Pennsylvania to eastern Virginia for M. grandii, and in Ohio for D. terebrans. All 3 exotic parasitoid species were retrieved at less than 3% of the sample sites. Data suggest that the dispersal rate of L. thompsoni from Delaware was about 50 km per year. An uncommon native Lixophaga sp. was found in western Ohio and western North Carolina. The 3 exotic parasitoid species appeared to be well established in their respective foci of abundance.