TOC INDEX Stable Fly Management for Feedlot Cattle Douglas D. Colwell Take Home Message Stable flies are blood-feeding insects that have a serious impact on production in feedlots. Losses can be substantial, exceeding $25M annually. Effective management requires an integrated approach that includes: sanitation to remove sites where females lay eggs and maggots develop; application of chemicals to surfaces for reduction of adult numbers; monitoring fly populations on cattle, to determine timing of insecticide use, is a valuable tool in the management of these biting flies. Introduction Stable flies are very important as summer and early fall pests of confined cattle in feedlots. Because of their biting habit and their very low host specificity they can also be significant pests in urban or recreational areas and thus may represent a liability for feedlot operators. The flies will live in any habitat that has a source of breeding material for the larvae and resting areas for the adults. Stable flies will obtain their blood meal from a variety of sources including cattle, horses, people, dogs and swine. Cattle, horses, and people are typically bitten on the legs; dogs and swine are generally bitten on the ears. Both sexes feed on blood, and the bites are extremely painful and cause severe irritation. Livestock react to the bites and activity of stable flies by twitching their skin, stamping their feet, and flicking their tails. This disturbs the flies during feeding, causing them to take flight. Flies will quickly return to the host to resume feeding. As a consequence of the host behaviour the flies make numerous visits to the host, and make repeated bites in order to obtain a full blood meal. When the flies have finally taken a full meal they will rest nearby in protected areas, particularly on vertical surfaces such as vegetation, fences, feed bunks, or on the sides of buildings. Alberta Feedlot Management Guide 2W2:1
Biology Figure 1. Life Cycle of the Stable Fly. Stable flies have 4 life cycle stages; egg, larvae, pupae and adults. The adult fly is about the size of a house fly, but it is dark gray and has dark irregular spots on its abdomen. Stable flies are easy to recognize because the biting mouthpart (known as a proboscis) protrudes in front of the head like a bayonet. The larvae or maggots have three stages each larger than the one before. The maggots in their last stage are yellowishwhite, 5 12 mm long and taper from the rear towards the head. The narrow head has two dark bars visible. These are the mouthparts. At the rear of the maggots are two large spiracles, or breathing holes. These distinctive features are dark black. The pupae are chestnut brown, roughly cylindrical and about 10 mm long. The complete life cycle of the fly from egg to adult can take 14-24 days during hot weather. In Alberta, there are as many as 3 generations of flies per season. The first flies will be observed in May and they will persist through to October. The overwintering part of the stable fly life cycle is not completely known. Some larvae do over-winter below the frost line. As temperatures rise, the larvae move toward the soil surface pupate, and thus give rise to at least some of the adults of the first generation of the season. There is some speculation that part of the first generation migrates from the south each spring. Stable flies are capable of moving considerable distances, but there is no documentation that a migration occurs. Female flies deposits eggs in spoiled or fermenting organic matter mixed with animal manure and dirt. The most common breeding sites in feedlots are around feed bunks, along the edges of feeding aprons, under fences and along stacks of hay and straw. The most common breeding areas outside of the lots are the drainage ditches leading to holding ponds. The ponds themselves, if properly designed and maintained, do not provide a fly breeding area. Slopes should be steep, they Alberta Feedlot Management Guide 2W2:2
should not fill with solids, and they must be kept free of weeds. If fly breeding is occurring at the edge of the drainage channels and irrigation water is available, the channel can be flooded to drown the flies. Economic Losses The bite of the fly is painful and cattle attempt to dislodge flies by foot stamping, tail switching and by throwing their heads down toward their front legs. When flies are abundant, cattle bunch (each animal trying to get to the centre of the group) or seek water to stand in to avoid the fly harassment. Heavy fly populations during hot days may cause cattle to go off feed. This severe situation can lead to digestive complications. Weight gain depressions of 0.48 pounds per day have been recorded. Stable fly population levels of two flies per front leg (counted on the outside of one leg and inside of the other) is the economic injury threshold. This is the point at which weight gains are depressed. It is indicated by the change in cattle behaviour as indicated above. Symptoms and Diagnosis As the periods of fly abundance vary from year to year, populations must be monitored routinely to determine optimal times to apply control methods. The simplest monitoring method is to count the number of infested legs (either by presence of flies or leg twitching and stomping) in a sample of 30 legs (15 animals). Intervention should be considered when 40% or more (12 legs) are infested. Management Sanitation is the first step in a stable fly control program. Manure should be removed or mounded and packed. Clean around feed bunks and feed aprons, under fences and gates, around water systems and at the edges of the mounds. Clean sick pens and feed storage areas regularly. Even small breeding areas support very high numbers of flies. If sanitation is not practised, chemical control may be unsuccessful. As an adjunct to sanitation there are several methods of reducing stable fly numbers with insecticides. Alberta Feedlot Management Guide 2W2:3
Residual sprays Stable flies rest on shady surfaces such as fences, feed bunks, buildings and vegetation surrounding feedlots. These surfaces can be treated with insecticides formulated as residual sprays. Flies resting on the treated surfaces and absorb the insecticide. Residual insecticides should be effective for 10 days, but may be washed off by rain, broken down by high temperatures or bright sunlight. Animal sprays Treatment of animals for control of stable flies is rarely practical in a feedlot. However, several products are registered for use as animal sprays and they will give relief from fly attack when densities are high. Biological Control The use of small parasitic wasps for control of feedlot flies, including the stable fly, has been used to a limited extent. These wasps search out fly pupae and lay their eggs on them. The wasp larvae develop within the pupa feeding on and killing the fly larva inside. Several companies sell house fly pupae containing developing wasps which are currently produced by commercial insectaries in the USA. This approach requires placing several thousand parasitized pupae at several locations in the feedlot. The intent is to increase rates of fly pupa parasitism and reduce stable fly adult populations. Under natural conditions the wasps are parasitizing fly pupae at a rate of 1 to 4 percent early in the season. The wasps currently utilized by commercial insectaries are not adapted to Canadian environments and there have been no independent evaluations of their effectiveness. Control Products Table 1 lists fly control products. Always consult package inserts and follow directions for preparation of product. Adherence to withdrawal times and safety considerations is very important. Reference 1. Lysyk, T.J., Philip, H.G. and Colwell, D.D. 1999. Recommendations for the control of arthropod pests of livestock and poultry in western Canada. LRC Mimeo Report 11. Agriculture and Agri-Food Canada, Lethbridge Research Centre. 115pp. Alberta Feedlot Management Guide 2W2:4
Table 1. Fly Control Products. Product Active ingredient Administration Tempo cyfluthrin Residual spray Diazinon diazinon Residual spray Disvap cichlorvos Residual spray Cygon, Lagon cimethoate Residual spray Cythion, Malathion malathion Residual spray Ambush malathion Residual spray Disvap II crotoxphos + dichlorvos Animal spray Disvap III dichlorvos Animal spray Several names pyrethin Animal spray Guardian flucythrinate Ear tag Alberta Feedlot Management Guide 2W2:5