Authors: Roger R. Youngman, Entomologist, Virginia Tech, E. Craig Turner, Jr., Entomologist, Virginia Tech Paul L. Ruszler, Poultry Scientist, Virginia Tech
Publication Number 444-769, Posted February 1999
Additional Rearing and Release Tips
Commonly called the black garbage fly or dump fly, Ophyra aenescensis a shiny black fly that is slightly smaller than the house fly. It typically can be found inhabiting garbage dumps and poultry manure like the house fly; however, unlike the house fly, it prefers darker areas such as the manure pits of cage layer houses. It is for this reason that it does not readily enter the upper floors of layer houses or, for that matter, nearby homes. Decaying organic matter or chicken manure are preferred egg laying sites of Ophyra aenescens female flies. The larva or maggot of Ophyra aenescens lives and feeds in a manner similar to the house fly maggot, but it also is a voracious predator of house fly maggots, making it an important biological control agent in high rise poultry houses.
A four-year study in Virginia has shown that mass rearing and inundative release of Ophyra aenescens pupae and maggots in high rise poultry houses was effective in reducing house fly populations. The program significantly reduced the cost and amount of insecticides needed, and, in some cases, eliminated the need for any additional chemical control intervention altogether. The following information on insectary establishment, mass rearing, and release of Ophyra aenescens in an IPM program, will help keep house fly numbers at low levels resulting in fewer complaints by homeowners.
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For best results in mass rearing the house fly predator, Ophyra aenescens, the size of the rearing room, or insectary, should occupy no less than 144 square ft. (i.e., 12 x 12 ft.) with an 8-ft. ceiling. To prevent the buildup of lethal levels of ammonia gas in the insectary, install a l0 inch diameter (or larger) exhaust fan in the middle and near the ceiling on one of two opposing walls. Directly across from the exhaust fan on the other wall, install a tightly-screened, air-intake vent.
Because a constant air temperature of 80-85 degrees F is critical to optimum rearing conditions, install a thermostatically-controlled heater inside the insectary. In addition, attach 48-inch fluorescent light fixtures to the insectary ceiling to maintain proper lighting 24 hours a day, and place 12-inch-wide shelving, at 8 to l-inch vertical spacings, on the inside walls of the insectary.
Because of their high reproductive rate, house flies can become a serious contaminant in the insectary during times when the predator fly colony is small or in the process of being built up. To minimize this, both a screened inside door and solid outer door must be mounted on the insectary. Additional measures against contamination can be achieved by installing an enclosed, outer hallway (4 x 4 x 8 ft.) and door. It is also important that the insectary be kept as clean as possible to prevent the establishment of unwanted insects and spiders. Obviously, insecticides cannot be used in the insectary to control unwanted pests.
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| Materials | Costs |
| lumber and hardware | $326.83 |
| exhaust fan | $20.75 |
| electric heater | $50.00 |
| sink (double laundry tub), faucet, and other hardware | $40.00 |
| insulation | $25.00 |
| labor (30 hrs @ $6.00/hr) | $180.00 |
| Total initial costs | $642.58 |
1 Because this insectory was built in the basement of a layer house, only lumber for shelves and walls was required. Costs compiled by Brenda Garner and Dale Mounce, plant managers, Glenwood Farms, Jetersville, VA 1986. A recent on-farm insectary was constructed from a surplus trailer.
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Adult
Larval
* Most of these can be obtained at local hardware or grocery stores for a total cost estimated between $500 and $600.
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Ingredients:
Recipe:
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Ingredients:
Recipe
1. The following table lists the proportional amounts of each ingredient in the media:
| Ingredients | Plastic-pail quantities (ounces) | Bulk1quantities (lb.) |
| wheat bran (coarse)2 | 17.6 | 55 |
| vermiculite3 | 8.8 | 28 |
| 50% powdered meat products | 5.3 | 17 |
| Totals | 31.7 | 100 |
1 Some producers use a small, portable cement mixer for both bulk mixing and pouring of media into the larval rearing trays.
2 Wheat bran and vermiculite also can be measured in equal parts by volume.
3 Sawdust can also be used as a cheaper alternative to vermiculite.
2. Add enough water (warm if possible) to the mixture until its consistency is very moist, but not soupy.
3. Pour the finished media no more than 2-inches deep into each larval rearing tray.
4. Lightly stir the contents of one chicken egg into the top of the media in each tray (the egg is an attractant for egg laying adult flies).
5. Label all trays with the date and place them in the insectary.
6. The rearing media must be kept moist until the larvae begin to change to the pupal or resting stage. If the media begins to dry out, add enough water to restore it to its original moisture level.
The estimated cost for the larval rearing media is about 27 to 30 cents per tray. The following are approximate costs for each of the ingredients in the media: $8.00/100 lb. of wheat bran; $12.00/14 lb. (4 cu. ft.) of vermiculite; $14.75/100 lb. of powdered meat products.
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1 Costs compiled by Brenda Garner and Dale Mounce, plant managers, Glenwood Farms, Jetersville, Virginia 1986. |
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The fly stage of Ophyra aenescens lives about 14 days compared to about 30 days for the house fly. The predator fly is maintained loosely in the insectary and allowed to lay eggs in the trays containing the fresh larval media. Fresh trays should be placed near the adult feeding cups on the floor for the first 24 hours, after which they should be placed on the shelves. The number of trays to be placed in the insectary is based on the number of predator flies observed in the room at any one time and the number of larvae in the trays. If few predator flies are observed in the insectary and predator larvae in the rearing trays are difficult to find, add only 2 or 4 rearing trays. As the numbers increase, begin adding more trays. Overcrowding occurs when larvae begin crawling out of the trays. This situation can be remedied by adding more trays.
By locating the insectary on the premises of a poultry operation, predator flies can be released in the poultry houses several times a week. Trays containing larvae or pupae can be taken to the poultry houses for release about 6 to 12 days after being placed in the insectary (hence the reason for recording the date on the newly-prepared trays). Trays that contain mostly larvae can either be emptied directly on the wet manure, or, if they contain mostly pupae, set in the manure pits for several days. This will allow the adults to emerge and find their own favorite breeding spots (the same as house flies). Never release more than half of the trays on any one date. The other half should remain in the insectary to keep the colony strong. A weak colony is at risk of being overwhelmed by house flies (much the same as in the poultry houses). Should this problem occur, reduce the number of releases until the colony regains its former level of productivity.
The best time to start releasing predator flies is when the house fly population is small. This can either be in the winter months or after several weeks of treatment with LarvadexTM feed-through insecticide. Begin making releases of predator flies about 2 to 3 days after withdrawal of the LarvadexTM treatment. During the summer months, the house fly population will increase dramatically, making it extremely important to release as many predator flies as possible to maintain dominance. Pay particular attention to wet spots in problem houses because this is where the house fly buildup will occur.
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