Geographical and temporal variation in pteromalid (Hymenoptera: Pteromalidae) parasitism of Stable fly and house fly (Diptera: Muscidae) pupae collected from Illinois cattle feedlots

Stable fly, Stomoxys calcitrans (L.), and house fly, Musca domestica L., puparia were collected at cattle feedlots in southcentral and northwestern Illinois from May through August 1991-1993 to determine the prevalence and species composition of pupal parasitoids (Hymenoptera: Pteromalidae). Additional samples of puparia were collected in September 1991 and October 1993. Parasitoids emerged from 10.6% of nearly 13,000 stable fly puparia and 13% of >17,000 house fly puparia. Spalangia nigroaenea Curtis was the most common parasitoid of the stable fly and of the house fly, comprising approximate to 60% of the parasitoids that emerged from the puparia of each species. Spalangia endius Walker was the 2nd-most prevalent parasitoid overall, comprising 14.2 and 18.4% of the parasitoids recovered from stable fly and house fly puparia, respectively. Parasitism by S endius varied greatly from year to year and between regions. Spalangia nigra Latrielle represented a much greater portion of the parasitoids recovered from stable fly puparia than house fly puparia (16.1 versus 3.8%). S. nigra also was more common in northwestern than southcentral Illinois. Spalangia cameroni Perkins was recovered every year, but represented only 3.1 and 2.8%, respectively, of the parasitoids recovered from stable fly and house fly puparia. Muscidifurax spp. (M. raptor Girault & Sanders and M. zaraptor Kogan & Legner) comprised 6.8 and 14.8% of the para sitoids recovered from stable fly and house fly puparia, respectively. Seasonal patterns of parasitism varied from year to year and between regions, probably in part because of substantial differences in weather each season.