Ohio State University Extension Bulletin

Livestock and Livestock Building Pest Management

Bulletin 473

Using Fly Parasites with Chemicals

Although fly parasites are an integral part of a good Integrated Pest Management (IPM) program, insecticides will still play a role in your control program. Insecticide use should be restrained.

Fly parasites are tiny wasps that kill fly pupae. They attack only fly pupae in manure and are so small (similar in size to gnats) they go unnoticed by humans and livestock. Farmers make frequent releases of small numbers of these beneficial wasps to augment their existing populations of beneficials. The wasp females seek out fly pupae, kill them, and then lay eggs within the dead pupae. These eggs hatch and mature into a new generation of beneficial parasitic wasps. Fly parasites are useful for the control of house flies, stable flies, blowflies, and many other fly species. They cannot sting nor bite humans or animals.


Natural Pyrethrins

Natural pyrethrins should be used as a "knockdown" spray. They have no residual effect and are an excellent tool in killing adult flies. If you have a serious adult fly problem now, it is recommended that you use natural pyrethrins to get the adult population under control before introducing fly parasites.

Synthetic Pyrethroids

Synthetic pyrethroids have a residual kill of up to two weeks or more and can be used to treat areas where adult flies roost, such as walls and columns. They should not be used as a fog or mist nor applied to manure. Permethrin is highly toxic to parasites and should be used with caution.


Baits such as methomyl or trichlorfon can be used to control migrating adult flies. They work by attracting the adult fly and kill it when ingested.

Care should be taken when using adulticides. Avoid overuse or resistance may develop. Also, remember that these pesticides will kill fly parasites as well. Use these pesticides wisely and sparingly.


Larvicide use should also be limited. Again, most larvicides will kill beneficial insects as well. However, if you have a "hot spot" of heavy fly larvae, larvicides can be used without inflicting much damage on the overall beneficial insect population. Insect Growth Regulator (IGR), such as cyromazine (Larvadex), approved for poultry operations does not affect beneficial insects. It only kills the fly larvae. This is the only larvicide that does not harm beneficial insects and can safely be applied to the breeding site without fear of destroying the beneficial insect populations.

Manure Management

In the summer, the fly life-cycle takes about two weeks: one week for the larvae to develop, and one week to pupate before emerging as new adults. On many dairy farms, calf bedding is a major fly breeding site. Weekly removal and spreading of manure disrupts the fly life-cycle, and prevents new adults from emerging in and around the barn. Removing the manure also helps the parasitic wasps, which find fly pupae more easily if the depth of the manure is relatively shallow. Leaving some surface manure behind when you clean out will keep the new generation of wasps in the barn.

Other breeding sites

Any accumulation of wet feed or bedding is a potential fly breeding site, and should be removed weekly.


Sticky paper, tapes, or ribbons and bait traps will help reduce the adult fly population without hurting the natural enemies.


Advantages of fly parasites are ease of application, reduces the need for chemical pesticides, prevents buildup of resistance to chemical pesticides, prevents immature flies from maturing to adult flies and is cost-effective. With application, there is no equipment, no mixing, no feed additives. Simply sprinkle them out of the bag onto the manure or staple to posts or rafters near areas where fly breeding is a problem.


Parasite release costs are usually offset by reduction in insecticide treatments. In research trials, dairy farmers using fly parasites have made as much as 80 percent fewer insecticide treatments with 50 percent lower fly populations than on conventional insecticide control farms. There is still much to learn on using fly parasites most effectively in fly management programs.

Prices vary from company to company on fly parasite purchase prices. Approximate costs are as follows.

Number of Pupae per shipment PriceShipping and Handling
Multiple Colony Shipments
Number of Colonies

Multiple Releases

Flies have the ability to produce more eggs, produce a new generation in a much shorter period of time and travel much greater distances than fly parasites. Consequently, it is best to release small amounts of fly parasites throughout the fly season rather than just one large release. Make weekly releases of 250 wasps per animal from mid to late May to August or September. (Some release 200 parasites per milking cow or 1,000 parasites per calf). However, each farm is different. Commercial farms that generate large quantities of manure should import fresh parasites weekly. For small farms, choose a biweekly, triweekly or monthly schedule.

Many companies who sell parasites advertise their products in farm magazines, but not all of them sell the right species adapted for the Ohio climate. Dairy farmers should purchase Muscidifurax raptor and avoid Nasonia vitripennis. Existing data indicates that in the Midwest the recommended species are as follows:

Fly Parasite SpeciesFlies Attacked
Muscidifurax raptorHouse and Stable Fly pupae


An outdoor species that also works indoors. M. raptor prefers dry, dark habitats and is active almost year-round, preferring cool temperatures and readily reproducing on late-season freeze-killed fly pupae. It has the potential to parasitize 20 fly pupae per day for one to four weeks. Early season inundatives releases have been helpful against house flies. M. raptor populations increase in late September and October when temperatures drop.

Spalangia nigroaena Stable Fly pupae preferred.
Also attacks house fly,
horn fly,
little house fly,
dump fly,
false stable fly, etc.


Works well against both stable flies and house flies. S. nigroaenea digs deep into manure where stable fly pupae are found. (Muscidifurax stays nearer the surface where house fly pupae are more commonly found.) Populations peak in summer, often July and August when fly populations peak.

Muscidifurax zaraptor House Fly pupae preferred.
Also attacks Stable Flies.


Often the dominant parasitoid species in Midwest feedlots. Considered best against house fly pupae. Early season spring releases show promise. M. zaraptor moves out evenly from release sites killing off concentrated house fly populations within 50 feet of release sites.

For additional information, contact:

Beneficial Insectory
14751 Oak Run Road
Oak Run, CA 96069
Telephone: 800-477-3715

IPM Laboratories, Inc.
Main Street
Locke, NY 13092-0300
Telephone: 315-497-2063
Fax: 315-497-3129

Fly Pro
Box 7
Kendall, KS 67857
(produces stable fly parasites, Spalangis nigroaena)

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