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House Flies

House Fly Adult
House Fly adult
House Fly Adult
  House Fly Larvae (maggots)

Biology

The house fly is the major pest species associated with poultry manure, especially in caged-layer operations. Suitable fly-breeding conditions are present year round in high-rise houses because of long-term manure accumulation and controlled temperatures. Even though flies appear to have no direct effect on production, they are a concern to poultry producers because they can cause public health problems resulting in poor community relations and possible legal action. The effective house fly dispersal range appears to be 1/2 to 2 miles, but distances as great as 10 to 20 miles have been reported. Generally, flies disperse either across wind or into the wind with nuisance densities highest closest to the source.

House flies can transmit more than 100 human and animal disease-causing organisms, including protozoa, bacteria, viruses, rickettsia, fungi, and worms. House flies are considered intermediate hosts for tapeworms and may transmit ascarids to caged birds. Flies mechanically carry ascarid and other nematode eggs on their feet from manure to pens, feed, and water. Fly maggots ingest tapeworm and ascarid eggs from the poultry manure and retain them in the gut until maturity. In turn, infected flies are ingested by the feeding bird. Although it appears that avian influenza is spread principally by contaminated shoes, clothes, and equipment, the virus has been isolated from adult house flies.

House flies are nonbiting flies about 1/4 inch long, mostly dull gray in color, with four black stripes on the thorax. Mouthparts are spongelike and are used for ingesting liquid foods. House flies breed in manure, spilled feeds, and other moist, warm, decaying organic material. Each female can produce up to six batches of 75 to 200 eggs at 3- to 4-day intervals, laying the eggs in cracks and crevices under the surface of the breeding material. Larvae (maggots) hatch from the eggs in 12 to 24 hours. They are white and cylindrical, tapering in the front. Maggots complete their development in 4 to 7 days, passing through three growth stages, or instars, as they grow larger. Mature larvae form a dark reddish-brown hardened case, called a puparium, from the larval skin and then pupate. The pupal stage usually lasts 3 to 4 days, after which an adult fly emerges to complete the cycle. Generations overlap; all stages are present at the same time. The life cycle is temperature dependent, requiring 10 days at 85°F, 21 days at 70°F, and 45 days at 60°F.

Adult flies live an average of 3 to 4 weeks, but they can live twice this long. They are most active during the day at temperatures of 80 to 90°F and become inactive at night and at temperatures below 45°F. Resting adults can be seen on ceilings, walls, posts, and other surfaces inside a poultry house, as well as outside beneath roof overhangs and on walls, fences, and vegetation. Preferred resting places can be detected by the accumulation of "fly specks," light-colored spots formed from regurgitated fluid and darker fecal spots.

Monitoring

A standardized, quantitative method for monitoring fly numbers should be used for making control decisions. Visual appraisals of fly populations are subjective and misleading. Several sampling methods are available: the baited-jug trap, sticky ribbons, and spot cards.

A baited-jug trap can be made easily from a gallon plastic milk jug with four access holes (2 to 2.5 inches in diameter) cut equidistant around the upper part of the jug. A wire is attached to the screwtop for hanging. About 1 ounce of commercial fly bait is placed on the inside bottom of the jug; a bait containing the fly pheromone muscalure (Muscamone, Z-9- tricosene) is most effective.

Baited-jug Trap
Baited-jug Trap

The trap location is important for effectiveness and accessibility. In a high-rise house, baited-jug traps should be hung equidistant around the pit periphery about 3 feet above the floor. In a shallow-pit house, traps should be hung in a similar fashion from the ceiling or braces at the ends and outside aisles of the house. Traps should be examined weekly, the flies counted and removed, old bait discarded, and fresh bait added to the jug. An average count of 250 flies per week per jug may indicate the need for fly control measures. The trap is most effective for house flies, but little house flies and black garbage flies also will be recovered. Baited-jug traps are more expensive to operate than other sampling methods, but they offer greater sensitivity to fly population changes.

Sticky fly ribbons hung upstairs along the aisles are another monitoring method. The captured flies are counted weekly, and the ribbons are replaced. An average weekly count of 100 per ribbon indicates the need for fly control, although this level may be adjusted to fit the circumstances. Ribbons have several disadvantages. They can become ineffective after a few days because of the covering of flies and dust; they are messy to use; and their position is important. Never place fly ribbons near exhaust fans or light bulbs, as these can give you an incorrect estimate of fly densities.

Sticky Fly Ribbon
Sticky Fly Ribbon

Spot cards are 3- by 5-inch white file cards placed in the manure pit and fastened flush against braces, upper walls, or other fly resting areas (areas with large numbers of fly fecal and regurgitation spots). Cards should be left for a period of several days to a week, and the number of "fly specks" counted. One hundred or more spots per card per week indicates the need for fly control measures. The greatest advantage of the spot card is economy; however, the positioning of the cards is critical, and cards should be placed in the same position at each renewal.

Spot Card
Spot Card

Although all of these monitoring devices are effective, spot cards have the additional virtue of providing long-term historical records of fly activity. Old spot cards can be particularly helpful in resolving conflicts with neighbors over claims of increased fly abundance.

Management

Fly control is basically a manure management strategy. Dry manure, 50% moisture or less, reduces the suitability for fly oviposition and larval development. It also provides a desirable habitat for beneficial predators and parasitoids. Three basic management strategies (cultural/physical, biological, and chemical) can be integrated into a successful fly control program.

Cultural/Physical Control

The keys to cultural/physical control are moisture management, sanitation, and manure removal. The manure moisture level is the most important factor in fly control. Moist poultry manure is highly attractive to adult flies and provides ideal conditions for fly development. Fresh poultry manure is approximately 75 to 80 percent moisture, and flies can breed in manure with a moisture content of 50 to 85 percent. Moisture levels are affected by leaking waterers, condensation from noninsulated overhead water lines, improper ventilation, and seepage from the exterior. Leaking waterers are the major source of wet manure conditions, so waterers must be inspected daily. Inspection can be done effectively only by walking the manure pit on a daily basis and looking for wet spots.

If dry conditions are maintained, manure will form a cone-shaped mound as it accumulates, and only fresh additions at the manure cone peak will be suitable for fly breeding. Houses with scraper boards usually have drier manure accumulations than those without, but scraper boards are not effective if water leaks exist.

Ventilation (airflow) reduces manure moisture while also maintaining desirable air temperatures, removing gases such as ammonia, and providing fresh air. Exhaust fans located in the manure pit walls provide ventilation for environmentally controlled high-rise houses. With adequate insulation, proper temperatures (60 to 75°F) can be maintained in cold weather. Fresh air is brought in from ceiling inlets and is circulated through the chickens and over the manure in the pit. Exhaust fans placed on both sides of the pit can help reduce moisture.

Supplemental drying fans can be installed above the manure rows. Three-blade, 36-inch, direct-drive fans should be suspended by chains from the ceiling. They should be installed every 50 feet in a serpentine configuration, and should be hung at approximately a 15-degree angle from the vertical. Because chickens usually begin to produce droppings just before the lights come on in the morning, fans typically are run during daylight hours. No definitive cycle exists, though, and producers should operate the fans to obtain optimum results. Obstructions will greatly decrease fan efficiency, so covers should be cleaned as soon as any debris collects on them. Supplemental fans will greatly increase the drying of the manure—often to below 50 percent moisture content—and will reduce the number of house flies produced in the pit.

In-house composting is an additional tool that producers can use to manage insect populations in high-rise layer houses. Manure is agitated to incorporate oxygen and possibly a carbon source to aid in the composting process. This agitation results in increased temperature, an increased ammonia level, and decreased moisture content, all of which help reduce insect populations. The agitation can be accomplished in several ways, but the most practical uses a commercial hydraulic-powered manure turner such as the "Brown Bear." Turning the manure pile twice a week is usually adequate, but the best way to determine need is to take the pile temperature with a compost thermometer. The temperature should be at least 120°F before turning is implemented.

Composting has some drawbacks. Ammonia is released in high concentrations during the turning process, so appropriate protective devices should be used. Composting eliminates beneficial insects, so ceasing to compost once you have begun can cause large house fly outbreaks. Finally, because the "Brown Bear" can not continually turn high piles, you must clean out when the pile approaches 2 feet in height.

Another successful moisture-control tactic, employed in the first 8 weeks of manure accumulation, involves using a snowblower, vacuum leaf mulcher, or shovel to transport dry materials and feathers from the pit aisles onto the top of the accumulating manure cone.

Sound sanitation practices are also important in fly control. Dead birds must be removed daily and disposed of properly. Spilled feed and broken eggs left on the manure attract adult flies and pest beetles. Mowing grass and weeds adjacent to the poultry house eliminates resting areas for adult flies and allows full airflow through the fans.

Finally, proper manure management reduces fly buildup and maximizes the development of beneficial predator and parasitoid populations. Fresh manure that accumulates within 2 days after house cleanout is ideal for fly breeding, often causing a severe fly outbreak to occur 3 to 6 weeks after a cleanout during the fly season. Remove manure only in cooler months when flies are less active. Allowing manure to accumulate for long periods conserves beneficial arthropods and maximizes their populations.

During spring and summer, when fly and beetle dispersal is a major concern, manure that must be removed from the building can be piled and tarped to kill developing pests. It is important that the manure be sealed completely under the tarp and the pile be placed in direct sunlight. Seal the tarp by filling 4-foot-long sections of 4-inch PVC pipe with sand, capping them, and placing them on the edges of the tarp around the base of the pile. When uncovering the manure pile, take care to avoid inhaling the excessive gas that accumulates under the tarp. Following a minimum of 2 weeks under the tarp, manure can be spread on fields without concern for pest dispersal.

Biological Control

Proper cultural/physical control practices encourage poultry manure accumulations containing large populations of beneficial predators and parasitoids that can suppress house fly populations. In the Northeast, macrochelid mites and hister beetles are the major predators in caged-layer operations. Parasitoid populations are present at densities lower than those of the two predators.

The macrochelid mite, Macrocheles muscae domesticae, is the most common mite in poultry manure. The reddish-brown mite, slightly less than 1/16 inch in size, feeds on house fly eggs and first-instar larvae. It can consume up to 20 house fly eggs per day. Mites are found on the outermost layer of the manure, particularly at its peak. Macrochelids can cause substantial reductions in house fly numbers, but large mite populations are required for any appreciable impact. Efforts should be made, therefore, to conserve natural populations present in the manure. About 3 to 4 weeks of manure accumulation are necessary for mites to become established.

Macrochelid mites feeding on house fly eggs
Macrochelid Mites Feeding on House Fly Eggs

Another mite that may be found in poultry manure is the uropodid mite, Fuscuropoda vegetans. It feeds only on first-instar house fly larvae deeper in the manure, complementing the egg-feeding activity of the macrochelid mite on the manure surface.

The principal hister beetle in northeastern poultry houses is Carcinops pumilio, a small black beetle approximately 1/8 inch long. Both adult and larvae feed on house fly eggs and first-instar larvae. Its impact as a predator has been well demonstrated. Adult and immature hister beetles live in the surface layers of manure and forage for fly and mite prey. Like macrochelid mites, hister beetles do not seem attracted to fresh manure, and it may take 6 weeks for significant populations to develop. Another hister beetle, Gnathoncus nanus, is also present in lower numbers on poultry farms in the Northeast.

Carcinops pumilio adult and larva
Carcinops Pumilio Adult and Larva

During the spring, hister beetles appear to enter a state of dispersal and become attracted to black lights. Using pitfall traps placed directly under these lights, you can collect hister beetles in large numbers and release them into recently cleaned houses on the same farm. Construct pitfall traps of smooth-sided containers such as shallow pans that prevent trapped beetles from crawling out. Place traps on the surface of the litter in walkway aisles between manure piles, and suspend black lights approximately 18 to 24 inches directly above the traps. Building manure ramps along the sides of the pitfall trap allows beetles to climb to the edge and subsequently fall in. The lip of the collection pan must be 1/2" wide and free of manure to prevent immature litter beetles from falling into the collection pan. If it is necessary to exclude larger litter beetles, cover the trap with number 12 or 14 mesh or pass trap contents through a number 14 sieve. Collect trapped beetles at least every 3 days. Alternatively, beetles can be collected with commercially available traps.

Black light pitfall traps can be used to catch and move hister beetles among poultry houses on a farm.
Black Light Pitfall Traps can be Used to Catch and Move Hister Beetles Among Poultry Houses on a Farm.

Houses with manure older than 24 weeks often have high enough populations of hister beetles to allow successful trapping. Beetles can be either transferred directly from a source house to a release house on the same farm or held at 45 to 50°F for up to 8 weeks. Beetles that are overcrowded, have too much moisture, or are held at too high or low a temperature will have decreased survival. Beetles in storage should be checked at least weekly. Carcinops pumilio can carry several poultry diseases; therefore, producers must not transfer beetles from houses with known disease problems. Captured beetles should be transferred only within a poultry farm.

Tiny, stingless parasitoids (parasitic wasps) attack most of the common manure-breeding flies. Parasitoids are rarely noticed because they are extremely small (1/16 to 1/8 inch) and occur naturally in low numbers on many farms. They live in manure or other decaying organic matter and search for fly pupae. Adult female parasitoids lay an egg on the fly pupa within the puparium. Here, the developing larva kills and consumes the fly pupa and emerges as an adult parasitoid.

Parasitoid adult and an M. raptor adult on a fly pupae
Parasitoid Adult and an M. Raptor Adult on a Fly Pupae
Parasitoid adult and an M. raptor adult on a fly pupae
Parasitoid Adult and an M. Raptor Adult on a Fly Pupae

Because of naturally low parasitism levels, control programs are sometimes based on mass releases of commercially reared parasitoids. Parasitoids are currently available from commercial insectaries and must be climatically adapted to the planned release area. For a release program to be successful, the producer needs to consider which species and strains, and in what numbers, to release. Releases of Muscidifurax raptor have been successful in northeastern poultry facilities. Another parasitoid, Muscidifurax raptorellus, may also be effective in caged-layer production systems. Releases of parasitoids from commercial insectaries such as Beneficial Insectary, Oak Run, CA (916-472-3715) and IPM Laboratories Inc., Locke, NY (315-497-2063) have been effective in Penn State and Cornell IPM programs. Producers must concentrate on conserving both their native and released predator and parasitoid populations by using proper manure management techniques and by minimizing insecticide use.

Parasitoids purchased from commercial insectaries arrive within days of expected adult emergence and should be released immediately into the poultry house. An effective release technique is to pour parasitoids (still in fly pupal cases) into paper cups and place the cups at the base of structural support posts. Distribute the parasitoids equally among the cups, and place a cup at every second or third post. If a particular "hot spot" of fly development is discovered, placing a few extra cups near the breeding area should aid in killing more of those fly pupae. Another method for releasing parasitoids involves hanging portions of the weekly shipment, in cheesecloth bags, from the manure pit rafters throughout the house. Release bags should be left in place for at least 3 weeks.

Proposed release schedules appear in Tables 2 and 3. It should be noted that the intensive release schedule presented is best suited for houses where flies have been a problem in the past and for farms in sensitive areas. Large releases may not be necessary in the fall and winter when fly dispersal is unlikely. Also, producers should consider releasing combinations of M. raptor and M. raptorellus.

Chemical Control

Producers must monitor fly populations on a regular basis to evaluate their fly management program and to decide when insecticide applications are required. Accurate insecticide and application rate records must be kept. Insecticides can play an important role in integrated fly management programs; however, improper timing and indiscriminate insecticide use, combined with poor manure management, poor moisture control, and poor sanitation practices, will increase fly populations and the need for additional insecticide applications. Although most fly insecticides are toxic to predators and parasitoids and can result in their destruction if used indiscriminately, selective application of insecticides can avoid killing these beneficials.

Insecticide applications may be classified by targeted fly stage (adulticides and larvicides) or method of application (sprays, baits, and feed additives).

Space sprays containing synergized pyrethrins provide a quick knockdown of adult flies in an enclosed air space. Because space sprays have very little residual activity, resistance to these insecticides is still relatively low among fly populations in the Northeast. Unfortunately, resistance has become a rather severe problem in poultry operations where pyrethrins were applied with automated dispensing systems. These poultry producers experienced loss of effective fly control in only one fly season. The key to successful fly management with automated dispensing systems is to use them sparingly. If you must use an insecticide, pyrethrins are currently your best choice for use as a space spray in an IPM program.

Baits are excellent selective adulticides for suppressing low fly populations and maintaining them at a low level. Baits are also especially effective when combined with space sprays. Place baits upstairs in a high-rise house, since scattering bait in the pit will destroy parasitoid and predator populations. Baits should be used so that they will not be eaten accidentally by birds or mixed into their feed.

Using feed additives to make manure toxic to fly larvae once was considered an attractive method of fly control because it was easy. Only one material, the insect growth regulator cyromazine, is currently registered for use in laying hens. While cyromazine does not affect predators and parasitoids, it can be expensive to use and has led to severe and long-lasting resistance in flies. In recent studies in New York, fly resistance to cyromazine was found to be widespread in poultry operations with a history of cyromazine use. Therefore, cyromazine should never be used as a replacement for other insecticides or for proper manure management practices.

Larvicides (pesticides applied directly to the manure surface to kill maggots) should never be used except for spot treatments, since they will destroy the predators and parasitoids associated with the manure. Cyromazine spot treatments of small areas with high numbers of maggots can be effective and yet have a minimal effect on the overall biological control agent population and fly resistance development in the manure.

Treating building surfaces with residual sprays has been a very popular fly control strategy over the years. Unfortunately, exceptionally high levels of fly resistance to insecticides used as residual sprays are now very common. Residual spray materials must be used sparingly and only as a last resort to control fly outbreaks that cannot be managed with other techniques.