Fly Control with Parasitic Wasps


Fly Parasite Bulletin

Fly Parasite Product Information

Make Your Own Adult-Fly Bait Station - Easy And Effective

Releasing Fly Parasites

Sagebrush Fly And Yellow Jacket Traps For Outdoor Use


Fly Parasite Bulletin



Rincon-Vitova Insectaries is a pioneer in growing beneficial insects to control flies in animal manure accumulations and other filth fly breeding sites. The species of flies that inhabit accumulations of manure are attacked by over 200 kinds of predaceous and parasitic species of insects, spiders and mites.

Combinations of these beneficial insects are attracted to manure, destroying all life stages. Beetles and mites devour fly eggs and larva. The adult fly stage is partially controlled by natural disease. The pupa (or cocoon stage) also has one of the most important natural enemies of flies: small parasitic wasps. Parasitic wasps find fly pupae with biological radar in manure and other fly breeding sites.

Our insectary mass-produces several species of tiny wasps in the genera Muscidifurax and Spalangia that attack fly pupae. Because each species in our mixture is adapted to different climates, we increase the proportion of Spalangia to Muscidifurax as seasonal temperatures rise. Hundreds of our satisfied customers from more than 20 years of service find our product helps reduce or eliminate the use of pesticides.



Parasitic wasps lay their eggs inside fly pupae and prevent the flies from emerging as adults. Immature stages of the parasites feed on the juices of the fly pupa. Adult parasites also prevent fly emergence by drawing fluid from fly pupae during host feeding. These parasites are very effective against the housefly, biting stable flies, garbage flies, and the lesser housefly, which comprise 95% of the flies in manure accumulations. These parasites will also attack blow flies and bottle flies breeding in and around garbage dumpsters. The parasitic wasps only attack flies and will not bite, sting, swarm or bother anything else. They are nocturnal and are rarely seen during the day. Fly parasites operate to a depth of 8 inches in manure, homing in with their biological radar on fly larvae that are about to pupate.

Fly parasites complete a generation every 3 weeks, (from parasitism of the fly pupa to emergence of the adult) thus at least three weekly releases are recommended to yield a steady production of adult parasites. With weekly releases, a noticeable reduction in flies can be expected in 4 to 6 weeks as the parasite population increases. They will eventually find and kill most of the flies at your location. However, because adult flies still can be migrating in, other control strategies such as trapping must be used. Biological control will work better for you if you and your neighbors use multiple strategies for fly control.





Flies have a much higher reproductive advantage than parasites; a single fly can lay up to 800 eggs a day, whereas a single parasite will attack less than 30 fly pupae a day. Flies also have an advantage of a shorter life cycle than parasites; 8 days in hot weather up to 14 days in moderate weather compared to 18 to 28 days for parasites. Adult flies are able to travel greater distances faster than parasites. The shorter life cycle also allows flies to become resistant to insecticides faster than parasites. By keeping the number of adult flies down, parasites will be better able to keep pace with the number of fly pupae. Because the fly has the edge, the population of fly parasites needs continuous reinforcement through augmentative releases of insectary-grown parasites in order to maintain a high level of fly control.



Trapping adult flies with baits is recommended to accompany fly parasite releases. Some chemicals or nonpoisonous materials are useful when they are formulated into sugar baits. Bait traps can be economically and safely used to remove large numbers of adult flies without interfering with biological controls. Baited jug traps are easy to make, very effective and keep the bait out of way of children and pets. Reducing the adult fly population early in the fly season (usually beginning after the first frost-free day of the year) give the beneficial population the time needed to increase to larger numbers in the manure and will result in fewer fly problems for the rest of the summer. Sources for purchasing and directions for making your own traps are available.

In humid areas and in wet manure accumulations, especially where manure is washed into pits, it takes both releases of parasites and bait stations to give excellent fly management. Set up at least one bait trap inside each barn or shady area where you see high numbers of adult (as indicated by fly specking) when you start releasing parasites. Trapping should continue with parasite releases until adult flies are gone.



Manure management

Good sanitation practices that eliminate conditions favorable to fly breeding are critical to limit fly problems. Frequent manure removal reduces the breeding sites. Keep areas around watering and feed troughs clean and dry. Maintain ventilation to keep manure dry and eliminate wet areas wherever possible.

Large amounts of manure can be managed in a pond or storage where non-aerobic digestion is accomplished or by aerobic composting systems. Unprocessed manure can be piled and covered. This reduces the surface and heat builds up to reduce fly breeding. Dry manure will not breed flies. The interface between wet and dry manure that has a moisture content of 50 to 80 percent is where fly breeding occurs. This is also where the fly parasites work best



Parasites are sent as approximately 10,000 parasitized pupae at approximately 75% parasitism to yield one standard colony (minimum 20,000 adult parasites). Factors affecting recommended numbers of parasites include numbers of flies, amount of manure or other organic matter, moisture content, humidity, temperature, existing beneficial controls, chemical usage, use of bait traps and incoming migrations.

Below are some suggested release rates based on the number of animals. Other factors to consider are temperature, moisture (rainfall) and the number of potential fly breeding sites. Fewer parasites may be needed during cool dry weather especially if other control strategies such as frequent manure removal and trapping adult flies are used

Schedules and numbers of units used in some typical programs: (1 unit = 1 FP10)




Amount suggested


100 parasites/horse

every 2-4 weeks during fly season

1-4 units/month for up to 30 horses


250 parasites/head

every 1-2 weeks during fly season

7-10 units/week for 1,000 head


200 parasites/cow, 1,000/calf

weekly during fly season

5-7 units/week for 100 cows

Poultry breeders

6 parasites/bird


5 units/week for 10,000 breeders

Poultry layers

4 parasites/bird


1 unit/week for 10,000 layers


500-1,500 parasites/cu. yd


5-15 units/month for 100 cubic yards


To develop a basic release program, increase or decrease suggested release rates based on these factors:




number of flies



manure or organic matter

a lot


manure moisture content



control measures established

no existing program

good program








could be better


animal watering equipment


no leaks




existing biocontrols (i.e. beetles, mites & fungi)



bait traps

don’t use


flies migrating in



flies hauled in (i.e. to composting sites)



comfort level with flies



neighbor’s comfort level with flies



budget for control



health concerns





It is easier to prevent a build-up of flies than to get rid of them. A few flies always survive the cold and drying conditions of winter in the pupa stage. Parasite releases should be made early each spring at the first sign of emerging or immigrating adults to minimize the numbers of adult flies laying eggs. Very early releases can be smaller in number, increasing in quantity at the first signs of active breeding. Once established fewer parasites are needed to maintain an effective number. A few may overwinter outdoors, but yearly augmentation is necessary.



These parasitic wasps arrive developing inside the fly pupa. When fully grown, they cut a hole in the pupa case and exit as adults searching for more fly larvae, seeking to lay their eggs where the flies pupate. The date on the bag is an estimated emergence date.

Sprinkle a small handful or spoonful of the parasitized fly pupae in wood shavings either on manure or in furrows and lightly cover to protect from birds. The widest possible dispersal around fly breeding areas is best.

Locating the fly breeding sites is critical to using the fly parasite effectively for fly control. Fly parasites should be released around any area where maggots are seen. Places to look for these sites are in and around coops, kennels, barns, stables, and stalls, with special attention to maternity, hospital and calf pens on dairies and fence lines and feedbunks on feedlots, and wherever straw bedding is provided for animals. Place also around corral posts, fence lines, paddock areas, and other dropping sites, at the edges of manure piles, pits or carts, and wherever manure accumulates. Other fly-breeding areas are near (but never directly in) water sources and decomposing matter in garbage cans and septic tanks.




Fly parasites must not be left in direct sunlight or hot areas. If ordered fresh, they may be held at 70° - 80° F, increasing to 85° F for more rapid emergence; otherwise, they are emerging and ready to release within a day or two. Cold storage shortens life and may harm reproduction. Avoid chemical sprays within 48 hours of release. Rincon-Vitova offers screen mesh release stations for hanging in barns where floors are washed regularly or predation by rodents is likely.





To assess the parasitism of fly pupae in manure, fly pupae can be separated from the manure by flotation in water. Agitation will float the pupae to the surface. Pupae that are old enough to have been exposed to parasitic wasps change from reddish to dark brown. Up to ten percent of these will not develop into flies. Those yielding flies have the end of the pupal case broken off. Neatly cut escape holes are evidence of parasitism. Check 100 dark brown pupae in a week for parasitism and dead intact pupae to get parasitism rate and possible parasite-induced mortality rate.



Since adult flies are the pest, a reduction in the number of adult flies is the best measure of a successful integrated fly control program. Control decisions should be based on a standardized method of quantifying fly numbers. Baited jug traps and index cards offer two standardized methods.


Counting the number of flies caught in baited jug traps or on fly tapes is an excellent way to monitor changes in fly populations. These traps are easily made by hanging a gallon milk jug that has four 2-2½ inch holes in the top half of the with a wire. One ounce of bait should be placed in the bottom of each

trap. Baits containing the fly pheromone musalure (Muscamone®,Z-9-tricosene) are the most effective at attracting flies. These traps should be hung about 1 foot below beams near areas where flies are often seen resting or where fly specks are concentrated. The trap should be emptied weekly and the number of flies caught counted. In general, fly activity is considered high if more than 250 flies are caught in a trap in a week.


Weekly placement of 3 X 5" plain index card near fly resting areas as indicated by fly specking provide an inexpensive method for monitoring fly populations as well as a historical record of fly activity. These cards should be fastened flush to a surface where fly specks are concentrated. Cards should be placed in the same position at each renewal. In general, fly activity is considered high if each card on average has more than 50-100 spots in a week.



Biological control works because of the entire complex of insectary-grown and naturally-occurring predators and parasites of all stages of flies. All natural enemies of flies are susceptible to pesticides, particularly when directed at manure. Reduce adult populations with poison baits. Spray only adult fly resting areas with long residual pesticides. This way you keep biological control working for you and reduce the need for insecticides.


Helpful Hints for Fly Control

1. Release enough fly parasites early, when flies appear and before it warms up.

2. Disperse parasites widely, concentrate releases where fly breeding is seen.

3. Trap adult flies. Place traps 2-3 feet above ground.

4. Clean manure, leaving a pad or reserve in which beneficial organisms have built up.

5. Eliminate wet areas where possible. Use hydrated lime where animals urinate frequently. Keep manure dry with good ventilation and clean up feed spills where possible.

Make Your Own Adult-Fly Bait Station - Easy And Effective


To get started, find -

A medium to large plastic bucket

Fiberglass window screen approximately 24 in. by 42 in.

A dowel or narrow stick approximately 3 ft.

Twine or duct tape

A quart of molasses

A spray bottle with tap water

A can of dry Fly Bait (may be purchased In pound cans at your feed store)

Then -

1. Wrap fiberglass screen around the bucket and overlap (fold over twice to seal the seam)

2. Fasten lower edge of screen to top edge of bucket with twine or tape to keep flies out! If adult flies enter, they will contaminate the molasses attractant.

3. Mix well 1 quart of molasses In 3 quarts of water in bottom of bucket to be fly attractant. Replace water lost by evaporation In molasses solution when necessary.

4. Place dowel stick In bucket to support screen, then fold over top edge of screen to seal.

5. Using tap water in spray bottle, wet screen all around.

6. Sprinkle wet screen with DRY fly bait so bait sticks to screen. Replace bait as needed.

7. Place bait station In areas where flies congregate and move to determine best site— shady locations In summer and sunny locations In winter. Station may be hung out of the way by attaching wire with hook to the sides of bucket.

8. This bait station functions without care for up to S weeks provided molasses mix continues to grow yeast Instead of putrefying bacteria.


---Keep station out of reach of children and pets.

---Label station "POISON!"

---Follow safety precautions on fly bait label.

—Wash hands after work with the station.

Adapted from Agricultural Extension Bulletin, San Bernardino County, CA, June 1974.



Fly Parasite Product Information

Minimum Contents: 10,000, 20,000 or 100,000 fly parasites (from 5,000 or 10,000 or 50,000 pupae); 75% minimum parasitism; no live flies. Approximately 50% wood shavings by volume.


Description: Small parasitic wasps are shipped developing inside fly pupae; some adults are emerging on delivery unless otherwise requested. Wasps will only attack fly pupae and do not bite, sting, swarm, infect or otherwise bother humans or animals. Wasps usually search under surface of decomposing organic matter.


Storage: Storage shortens life and may reduce reproductive capacity. If release must be delayed, open box and hold at 50º F (10º C) and 40-60% RH with good air circulation for a few days only.


Guarantee: Alive and in good condition. Open package and report any problems immediately.


Sex Ratio: M. raptorellus, 60% female; S. cameroni, 60% female

Host Pests: Housefly, biting stable fly, garbage flies and lesser houseflies, etc.

Development: Development: Egg to adult life span is 16 or more days depending on temperature.


Program Guidelines:

  • Used for augmenting the natural enemies already at work in decaying organic matter

  • Start at first sign of flies and keep up with regular releases till fall

  • Quantities can start low and increase with warm, wet or humid weather

  • Clean out manure at least weekly in areas where fly breeding occurs

  • Leave edges of organic matter to conserve breeding parasites

  • Trap adult flies to reduce quantities of parasites needed for release

  • Plan for an average of 250 parasites per large animal, or 1 parasite per bird per week


Release Guidelines:

  • Hold at 60º to 90º F (15º to 32º C) with good air circulation. Keep out of direct sun.

  • Ready to release immediately or within 48 hours unless receiving unincubated pupae.

  • Sprinkle widely around edges of organic matter where flies lay eggs and pupate.

  • Pouches of mesh or plastic can be used as release stations where damage or predation is likely.

  • Parasites are most effective around areas where flies are breeding (indicated by presence of maggots)


Pesticides: Susceptible to pesticides, particularly when directed at manure. Careful placement of pesticides minimizes harm. Reduce adult fly populations with traps or poison baits. When applying pesticides with long residual activity, spray only adult fly resting surfaces to minimize the impact on the parasites.


Genus, Species, Origin, Composition of mixture (Family: Pteromalidae)

Genus, Species, Origin, Composition of mixture (Family: Pteromalidae)

Muscidifurax raptorellus Kogan and Legner (50-75% of mixture) produces 4 – 6 parasites per fly pupa

Spalangia cameroni, Perkins, a cold-hardy and heat-resistant strain commonly found throughout the US. Since Spalangia thrives in hot weather, we increase the proportion of Spalangia in our mix in relation to Muscidifurax species as seasonal temperatures increase (25-50% of mixture).


Releasing Fly Parasites

These tiny wasps attack several species of filth breeding flies commonly associated with livestock. Besides being extremely effective, they are virtually unnoticed by humans or animals. The release of these parasites can have a dramatic effect on pest fly populations. The key to a successful fly control program is to start early, and make scheduled releases throughout the fly breeding season. Use of supplemental control methods such as sugar baits, fly traps, manure and breeding habitat management, etc. are strongly recommended. There are many factors that influence the quantity of fly parasites to be released in a particular site. Some of these are: the season of the year, weather conditions, suitability of manure or breeding media, number of animals in a particular area, migration of adult flies into the control area, etc.

To release the fly parasites, keep them in a warm place, about 70 to 80 degrees, and check for them hatching by simply opening the paper bag and looking for the small ant sized parasites moving around the bag. The parasites should emerge within the dates marked on the bag. When you see several crawling inside the bag, sprinkle the contents in the fly breeding area, usually in manure piles or moist areas. Fly parasites are packaged in 'colonies' of 10,000 or minimum orders of 5,000. Most customers receive shipments at intervals of 2 to 4 weeks.

Sagebrush Fly And Yellow Jacket Traps For Outdoor Use


1. Place trap over bait.

2. Fly enters through side holes to access bait.

3. Fly heads for light when leaving bait and travels through screen cone into containment area.

4. Fly is unable to escape containment and dies.

Longtime established and proven cone style design. Stainless steel clamp, aluminum screen, and galvanized steel. Bait with compost, manure, farm waste, and commercial fluid baits.

Large size for low maintenance.

Bucket not included


Place trap over bait. This model has a diameter of about 12 3/4" and can sit on top of a common 5 gallon bucket. Farm waste and commercial fluid baits can be placed in the bucket. A piece of screen can be placed over the bucket and under trap for preventing flies from breeding and dying in the bait. Place the trap so that light enters trap through the top. Some flies are particular to location so place the trap where flies are located. A wood open topped box can be constructed and placed around the trap to protect it from livestock when trapping ground hovering flies. When placed on a bucket, the bucket can be wired to a fence stake to prevent it from being knocked over. Remove dead flies by unscrewing the hose clamp and slipping the top off.

Some recommended baits include, fish, shellfish, chicken scraps, manure, compost, and commercial fluid baits (2oz/5gal Farnam Brand Fly Trap Attractant works good with horses). Meat baits work best when rotten and manure baits work best when fresh. Most baits will need to be kept wet for effectiveness so add water as necessary to keep the bait from drying out. Yellow Jackets are an easy catch and just about any odorous meat scrap or bones will work. Some varieties of flies are more particular and experimenting with baits may be necessary. Fluid baits are the least maintenance in hot dry weather.

H1 Hanging Model S1 Standing Model

Ideal for yellow Jackets using meat baits

Economy, holds larger baits


1: Fly enters through side holes to access bait.

2: Fly heads for light when leaving bait and travels through screen cone into containment area.

3: Fly is unable to escape containment and dies.


Long established cone style design.

All metal construction.

Bait with shrimp, fish, chicken bones, chicken wrappers, chicken or dog manure, compost, or commercial baits.

Fluid bait and larger standing traps, trap to sit on 55 gallon drum, also available.

Traps available from Rincon-Vitova Insectaries, Inc.

Produced in America by David Olkowski, SAGEBRUSH COMPANY