TIMING OF RELEASES OF GREGARIOUS MUSCIDIFURAX-RAPTORELLUS (HYMENOPTERA, PTEROMALIDAE) TO CONTROL FLIES ASSOCIATED WITH CONFINED BEEF-CATTLE

A gregarious strain of Muscidifurax raptorellus Kogan and Legner (Hyme noptera: Pteromalidae) colonized from house fly (Musca domestica L.) p uparia collected in eastern Nebraska was mass reared and released. The study was undertaken to determine dispersal rates, persistence of rel eased parasites, and optimal intervals for releasing this promising bi ological control agent for filth flies. A single release of 200,000 pa rasitized house fly pupae resulted in 96% parasitism of sentinel house fly pupae 2 wk after release. Parasite activity declined to backgroun d levels over the subsequent 3 wk. When two releases of 100,000 parasi tized hosts each were made 6 wk apart, parasitism averaged 70% and 55% , respectively, 2 wk after releases. When three releases of 67,000 par asitized hosts were made at 4 wk intervals, peak parasitism averaged 4 4%, 58%, and 80%, respectively, following the three releases. Parasite emergence from naturally occurring stable fly, Stomoxys calcitrans (L .), and house fly puparia (Diptera: Muscidae) averaged 15.5% and 37.2% , respectively, collected during the 3-wk period after each release, a nd little recycling was evident. Muscidufurax raptorellus is gregariou s and aggressive and can be reared at considerably less cost than soli tary pteromalid species. However, more study is needed to determine it s potential as a biological control agent of filth flies.