Larval mortality of the face fly, Musca autumnalis De Geer, due to the biotic environment in Virginia was determined to be approximately 62.7% during the sumer of 1967 in preliminary studies. This was based on the difference in numbers of pupae resulting from an insect~accessible tray and an insect~proof tray, Each was filled with bovine manure and both contained approximately equal numbers of eggs or new first—instar larvae when placed in the field,

Pupae of the major species of coprophagous Diptera resulting from pasture droppings of bovine feces were collected in sandboxes and furnels from three areas of Montgomery County, Virginie during 1967. The pupae were separated according to species, incubated, and examined afterwards to determine the fate of each pupas, Special emphasis was placed on the parasites involved and the portion of total porasitization contributed by each species, Primary interest was in biological reculation of face fly populations, Other flies were studied for comparison and to determine natural reservoirs of parasites, Comparisons of data from sandboxes with those from funnels showed a higher over-all rate of parasitism in the sandboxes than in the funnels. Other techniques for attempting to obtain new parasites of the face fly were also employed,

Adult face flies were examined for nematodes, Heterotylenchus autumnalis Nickle. Approximately 16% of the natural population were infested during 1966-7.

Available data for mortality during different life stages were combined into a preliminary life table for the face fly.

Muscidifurax raptor Girault and Sanders, a pteromalid parasite, was recovered in low numbers from face fly pupae during 1966 field studies, It has been successfully propagated in the laboratory on face fly pupae by mechanically cracking the fly puparia to aid emergence of the parasites, Parasitism is normally accomplished by penetration of the ovipositor throush the posterior spiracles of the host, The ovipositor of one female was observed to penetrate the anterior spiracle of a face fly pupa. Muscidifurax ravtor is not limited to the spiracles for penetration of house fly pupae.

Muscidifurex raptor was found on several hosts in nature. Eucoila sp., Xyalophora quinouelineata (Say), Aleochora tristis Gravenhorst, and A. bimaculata Gravenhorst, which are parasites of coprophagous Diptera, were hyperparasitized by M. raptor.

Studies on the biology and behavlor of M. raptor were conducted in the laboratoiy, Its effectiveness in parisitizing different hosts was compared on house fly and face Fly pupae.