Timing of Releases of Gregarious Muscidifurax raptorellus ( Hymenoptera : Pteromalidae ) to Control Flies Associated with Confined Beef Cattle '

A gregarious strain of Muscidi{urax raptorellus Kogan and Legner (Hymenoptera: PtcromaJidae) colonized from house fly (Musca domestica L.) puparia collected in eastern Nebraska was mass reared nnd released. The study was undertaken to determine dispersal rates, persistence of released parasites, and optimal intervals for releasing this promising biological control agent for filth nics. A single release of 200,000 parasitized house fly pupae resulted in 96% parasitism of sentinel house fly pupae 2 wk after release. Parasite activity declined to background levels over the subsequent 3 wk. When two releases of 100,000 parasitized hosts each were made 6 wk apart, parasitism avcmged 70% and 55%, respectively, 2 wk after releases. When three releases of 67,000 pnrasitized hosts were made at 4 wk intCl'vals, peak parasitism averaged 44%, 58%, and 80%, respectively, following the three releases. Parasite emergence from naturally occurring stable ny, Stomoxys c;alcitran.c; (L.), and house ny puparia (Diptera: Muscidae) averaged 15.5% and 37.2%, respectively, collected during the 3-wk period after each release, and little recycling was evident. Muscidu.furax raptorellfis is gregar'ious and ag!,'Tcssivc and cnn be reared at considerably less cost than solitary ptcromalid species. However, more study is needed to determine its potential as a biological control agent of filth nics.