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Biological Control : A Guide to Natural Enemies in North America Anthony Shelton, Ph.D., Professor of Entomology, Cornell University

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Muscidifurax raptor
(Hymenoptera: Pteromalidae)

An important control agent of filth flies, the parasitoid Muscidifurax raptor is thought to have been introduced to the western hemisphere along with the house fly and stable fly, which it parasitizes. It belongs to a large family of about 340 species and is the most effective parasitoid of flies on farms in the northeastern United States.


M. raptor is a minute, black wasp, about 1-2 mm long.


Dairy farms and poultry ranches, as well as suburban and urban localities where flies exist. M. raptor does well both in- and outdoors, and is best suited to controlling fly populations in the northeastern United States.

Pests Attacked

The house fly, the stable fly, and other fly species.

Life Cycle

The adult parasitoid stings the fly pupa, killing the pupa and then lays an egg in the pupal case. When the egg hatches, the larva feeds on the dead fly pupa. In 19-21 days, the M. raptor adult emerges from the fly pupal case and begins its search for fly pupae on which to feed and deposit eggs.

Fly Life Cycle
Parisitoid Life Cycle
Life cycle diagrams courtesy of Ciba-Geigy Corporation.

Adults feed on fly pupae body fluids. The female may sting the pupa, killing it, without depositing an egg. A droplet of fluid appears at the sting site, and the female feeds on the fluid and may share with a nearby male.

Relative Effectiveness

Flies live longer, develop into adults in half the time, and lay more eggs than M. raptor and are thus more numerous than the parasitoid. For control of flies, it is helpful to augment parasitoid populations in early summer. The optimal time to begin parasitoid releases is mid- to late May, and they should continue on a weekly basis until mid-August. In research trials, costs were more than offset by reductions in insecticide expenses.

In one study, adult parasitoids successfully developed in 70% of parasitized pupae, but even when adults failed to emerge, the fly pupae were killed. In addition, due to the adult feeding activity, more flies are killed than are actually parasitized.

Pesticide Susceptibility

M. raptor, having a longer life cycle, has not developed the resistance to commonly used pesticides that flies have developed. In many cases a pesticide will scarcely affect the fly population but will destroy its parasitoids. Research has shown that, in general, M. raptor is more susceptible than flies to insecticides. If insecticides must be used, space sprays and baits are most compatible with fly parasitoids.


The careful, proper use of insecticides (if necessary) and weekly releases of M. raptor along with proper manure management, should help establish a favorable balance of this parasitoid in relation to filth flies.

Commercial Availability

M. raptor is available from commercial insectaries. Care should be taken to obtain insects that are free from disease (microsporidosis).


Thanks to Wes Watson, Department of Entomology, North Carolina State University, Raleigh, NC 27695-7626, for providing material and for reviewing and making suggestions that have improved this section.


Geden, C.J., Rutz, D.A., Scott, J.G., Long, S.J. (1992) Susceptibility of house flies (Diptera: Muscidae) and five pupal parasitoids (Hymenoptera: Pteromalidae) to Abamectin and seven commercial insecticides. J. Econ. Entomol., 85: 435-440.

Smith, L., Rutz, D.A. (1991) Seasonal and relative abundance of hymenopterous parasitoids attacking house fly pupae at dairy farms in Central New York. Environ. Entomol., 20: 661-668.

Smith, L., Rutz, D.A. (1991) Relationship of microhabitat to incidence of house fly (Diptera: Muscidae) immatures and their parasitoids at dairy farms in Central New York. Environ. Entomol., 20: 669-674.

Watson, D.W., Waldron, J.K., and Rutz, D.A. (1994) Pest Management Fact Sheet. Cooperative Extension, Cornell University, IPM Dairy Management 102DMFS450.00. 4 pp.

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M. raptor on fly puparium.

M. raptor on fly puparium.

Photo: S.Long

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