Fly Predators Control Flies in Horse Facilities
by Debra J. Hagstrom, M.S., Equine Extension Specialist, University of Illinois
Fly season is in full swing and fly control should also be at its peak. There are various types of fly control which attack your fly problem from different directions. Are you utilizing the full arsenal of fly control measures to optimize the reduction of your fly population?
Before answering that question, we need to understand something about the pests we are battling. In horse facilities, house flies and stable flies are common pests found in areas where manure accumulates. Adult stable and house flies lay eggs on freshly deposited manure. Soon after, these eggs will hatch into larvae. The entire life cycle of the fly takes only 7 to 10 days in hot weather. An adult house fly may live for about 30 days and a female can lay up to 900 eggs. On horse farms and in stables, most flies are "home grown" so to speak. However, stable flies can also come to your farm from elsewhere. Research has shown that strong winds can carry stable flies up to 135 mile from their breeding site. Most stable flies, though, come from within a two mile radius of your own place if not from your place. In addition to manure, flies can breed in any decaying material such as grass clippings, old bedding, old round bales left on the ground, etc.
Fly predators or fly parasites are becoming a more common avenue of fly control for horse owners as they are safe for horses and gentle on the environment. Fly predators are a gnat-sized, nocturnal, stinger-less wasp that lays eggs in fly pupa. They feed on the larvae of the fly while it is still in the manure. Each female fly predator searches through manure seeking out fly pupa. She then drills a hole in the pupa case and lays several eggs inside. After these eggs develop into mature adults they consume the fly larva as a source of food, thus killing the immature fly and effectively breaking the life cycle of the fly. After feeding on the dead fly larvae, a new adult fly predator emerges from the fly pupa in 1 to 2 weeks. The new parasites then search out and kill more fly pupae. Each female fly parasite will kill about 100 fly pupae in its lifetime.
Fly predators are naturally occurring enemy of all manure breeding pest flies. However, they are usually not found in a large enough population to control an aggressive fly population. During the fly season these parasitic wasps must be replenished about once a month. They are simply not able to multiply in sufficient numbers to control the vast number of flies usually present around horse stable areas. One release of the fly predators can temporarily reduce the population of lies. However, because of the differences in the life cycles of the fly and the fly parasite, and because migratory flies continue to enter the control area, a program of periodic release coupled with other forms of fly control (chemical, feed-through, fly traps, etc) is required for ongoing fly control. Fly predators will travel up to 80 yards to find a food source (fly pupae) so keep that in mind as you are distributing them around the edges of "hot spots" – areas where manure and urine are accumulated and thus where flies are crawling and breeding.
Several species of parasitic wasps are available. Spalangia nigroaenea is the commercially available parasite that is most likely to attack both house flies and stable flies in the Midwest. Muscidifurax raptor and Muscidifurax zaraptor will provide some parasitism of house flies. Spalangia nigra, Spalangia cameroni and Spalangia endius will provide some parasitism of stable flies. It is not wise to buy "unspecified "blends of species since you don't know if you are getting the species that will best deal with your specific fly problem. Also, be aware that none of these fly parasites are effective again face flies, horn flies, deer flies, or horse flies.
Fly predators do not bite or sting humans or other animals and are so tiny that they go largely unnoticed. These wasps are harmless to animals and people so that they are a safe, non-toxic means of biological control both stable and house flies. Combined with traditional chemicals (fly sprays), feed through products, and fly sheets or masks, fly parasites are another tool that should be considered when fighting the battle against flies on horse facilities.
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