Fly Season is Coming! - Stable Flies

Part 1 of "Fly Season is Coming!" (or for many, is here), there could be no other fly worthy of being first than the stable fly. Not only is it the FIRST biting fly to emerge for the year (or if you live in the south, stay active all year) it is also a nasty biter that will take advantage of any bloodmeal it can get.

The stable fly is the most significant pest of livestock in America; because of its painful bite and blood feeding behavior, cattle self-inflict stress and injury trying to escape attack.  The impact of the stable fly is noticeable with populations of more than 20 flies per animal, which can adversely affect animal health and significantly lower income for livestock producers.  Evidence shows that heavy infestations of stable flies on beef cattle have reduced weight gain by 25 percent and, in dairy cattle, have decreased milk production by 10 to 20 percent. 
To suppress stable flies effectively and economically, it is important to:

• Be able to identify them properly;
• Understand the insect’s life cycle; and
• Use a combination of control strategies.

Identification

The stable fly, Stomoxys calcitrans, looks like the house fly, but it is smaller (1⁄4 inch). Unlike the house fly, stable fly mouthparts resemble a bayonet that can easily be seen protruding from the head.  The stable fly differs from the housefly in that it depends on blood as food and has an extremely painful bite. Stable flies primarily attack the legs of livestock and the ears of dogs.

An animal’s reaction to being attacked by stable flies consists of objectionable behavior such as stomping and kicking their legs, this makes it difficult to milk dairy cows.  Unrestrained animals will typically bunch together when attack, causing an increase in heat stress.  

Biology and habitat

The stable fly has a complete life cycle with egg, larval (maggot), pupal and adult stages. Populations can increase quickly: Under optimal conditions, the egg to adult cycle is about 3 to 4 weeks; therefore several generations can develop each year.  A female stable fly lives for 3 to 4 weeks and lays 500 to 600 eggs during its lifetime. 

The eggs are typically laid in wet straw, wet hay bales or in other decomposing vegetation mixed with urine and feces produced by the animals.

Management

To suppress stable fly populations efficiently, producers should use an integrated pest management (IPM) approach. IPM relies on three tactics for successful suppression of an insect pest: cultural, biological and chemical. 

Cultural control: Cultural control methods involve manipulating the environment to reduce insect pest populations. The most economical and effective method for suppressing stable fly populations is sanitation.

In confined animal facilities, a top priority should be to eliminate stable fly breeding sites as often as possible. To do this, remove and spread decomposing vegetation or bedding material that has become mixed with urine and feces. Spreading the bedding will allow the material to dry faster and prevent colonization by the stable fly.

Another tactic for confined animal areas is to design the stalls to allow for complete manure removal and drainage. Cleaning out the wet feed remaining in the ends of troughs should be done weekly because the wet feed serves as a breeding site for flies. 

For small to moderate fly populations of adult flies, sticky traps and other mechanical methods, when combined with sanitation, are effective in confined areas. However, sticky traps will not substantially reduce fly numbers if used alone. Sticky traps should be changed weekly because they become coated with dust or “saturated” with flies.

Spreading decomposing vegetation (unused hay) should also be implemented for range or pasture cattle. Throughout the year, hay bales are often provided as supplemental feed for cattle. Over the course of the winter, the sites where hay bales have been placed become ideal stable fly breeding areas. Using hay rings will help to reduce stable fly populations in the field/pasture by reducing the amount of wasted hay trampled into the soil.  Also, moving the feeding site regularly reduces the accumulation of wasted hay at a site and eliminates breeding sites.  Spreading the accumulated wasted hay, will help dry out the site and prevent continual stable fly breeding.

Sticky Traps: The use of sticky traps provides a non-chemical approach to controlling stable flies, both males and females. The sticky traps are attractive to the adult stages as a resting location during bloodmeal digestion but prevent the stable flies from leaving. These traps can be used at any number of facilities but are best placed out of reach of animals. 

                                        Olson Biting Fly Trap           Knight Stick trap

Biological control: This IPM tactic uses natural predators (fire ants), parasites (like the wasp Spalangia sp.) or pathogens (Bacillus thuringiensis) to suppress pests. 

The parasitic wasp, Spalangia sp., is available commercially.  The wasp lays an egg into the pupa of the stable fly. The immature wasp feeds on the pupa, eventually killing the pupa.  The wasp develops into an adult and emerges from the pupa to start the cycle again.  

At this point, there is no clear answer to the effectiveness of using parasites to reduce fly populations.  Chances for success are greatest when coupled with waste and water management, and chemical control as needed.  Chemical controls should be limited to sprays or other application techniques that will not come in contact with breeding sites and kill the parasites.  Wasp releases have to be conducted on a set schedule and are needed each year; do not count on establishing a population on your farm.  Wasps may supplement an integrated program based on sanitation but are unlikely to provide adequate control when numerous breeding sites are available.  

Chemical control:

If a stable fly problem persists, an insecticide can be used. Many compounds are available for suppressing adult and larval stable fly populations. Always read the pesticide label in its entirety before making any applications.  

Animals can be treated as needed with sprays containing permethrin (Catron, GardStar, Permectrin II, Permethrin and Tengard), Ravap® EC (23% tetrachlorvinphos) and Vapona® EC (40.2% dichlorvos).  Residual wall sprays such as Atroban® 11% EC (permethrin), Demon®WP (cypermethrin), Ravap®, and Vapona® can be applied to surfaces where the insects rest. These products can be used in backpack or truck sprayers for range or pasture cattle or used in misters daily on dairy cattle for protection against stable fly feeding.  Brahman and Brahman cross cattle should not be treated due to hypersensitivity to organophosphates.  One day withdrawal is required for beef cattle sprayed with Vapona®.

Many premise products are available (Annihilator®, Atroban® 11% EC, Brute®, Demon® Max, Durashield®, Elector® PSP, GardStar®, Grenade®, Permectrin II, permethrin, Rabon® 50 WP, Ravap® EC, Tengard®, and Vapona®) that can be sprayed around a livestock facility and on side walls that are used as resting sites for fed stable flies.  Always follow product labels for conducting premise spray applications.