Parasitic wasps are effective in controlling pests with multiple well-timed releases and when used in conjunction with sanitation.
Know the enemy
Fly pests and the corresponding treatments vary depending on the type of production system. Flies are a problem, but it’s not always the same species of fly in each situation. In the feedlot, the most common insect pests are the house fly and the stable fly.
House flies have different physiology than stable flies. Kelly Loftin, a professor and extension entomologist at University of Arkansas says, “The stable fly is a parasite found primarily on cattle rather than the premises. They are blood-feeding flies that are about the same size as the house fly but darker gray in color.
Unlike the house fly, stable flies have mouth parts similar to horn flies; their piercing mouth parts protrude from under their heads and allow them to take blood meals. Both male and female stable flies feed on blood.” The house fly, although a nuisance, only has a spongy mouth part and doesn’t bite.
Research has shown that without effective control measures, stable flies can reduce cattle gains by 20 pounds. Adult stable flies feed on the legs of feedlot cattle and can deter them from their main purposes – eating and gaining weight. One study reported an economic loss of 0.2 pound per day with as few as four flies per leg in feedlot cattle.
Sanitation is important in controlling flies in feedlots. Stable flies breed in manure and wasted feed; managing the accumulation of these can help prevent a flush of flies from hatching.
Fly control should be a multipronged approach. Sanitation, biologicals and chemical control are the prongs needed for success. Of these steps, biologicals are the one that consumers would find hardest to criticize.
Sanitation
The key to controlling flies begins with manure management. The problem comes from areas in the pens where conventional pen cleaning equipment can’t reach. Typically, undisturbed manure under bunks and fences around water provide the ideal environment for flies to breed. Flies can’t breed in dry manure, therefore drainage, properly scraped pens and maintenance of water supplies is important.
Stable flies and house flies both breed in manure on a continuous cycle during warm months. Their total life cycle is from 14 to 40 days.
Once fly breeding areas are diminished, then other management tools can be utilized to their greatest advantage. Decaying feedstuffs and weeds also provide fly habitat.
Biological control
Parasitic wasps are a complementary strategy that works well in feedlots and dairies but is less effective in pasture settings. They require fly eggs to complete their reproductive cycle. The fly parasites are introduced into manure and other breeding sites of flies.
The wasps are very small, about the size of a gnat, and use a stinger to lay eggs in the pupae of flies. These eggs hatch and feed on the fly larvae and emerge as adults after about two weeks. Wasps can lay up to 350 eggs per day and can drastically reduce the number of adult flies.
Parasitic wasps take about three weeks to complete a generation, compared to flies that can take less than 10 days – therefore, multiple release of wasps during fly season is more successful than releasing a large population once. To be successful, thousands of parasites are released simultaneously every week during fly season.
Parasitic wasps can be purchased from an insectary. Common species of parasitic wasps include Spalangia cameroni, muscidifurax spp., Muscidifurax zaraptor, M. raptorellus and Trichomalopsis sarcophagae. Loftin says, “Usually the commercial parasitoids you purchase will contain a mix of two or three species.”
Loftin says, “When buying commercial parasitoids, it is important to ensure that wasps survive shipping and are from a reputable source.” Loftin also recommends avoiding other parasitoid species such as Nasonia vitripennis, because research has shown poor dispersal and parasitism rates.
Insectary
Kunafin is a family owned-and-operated insectary in Quemado, Texas, located near the Mexican border, which serves feedlots in six countries.
Frank Junfin, owner of Kunafin, says, “I have been a student of biological control since I was a small kid going to cotton fields with my dad.” His dad, Joe Junfin, immigrated to the U.S. in the late ’50s and introduced beneficial insects to cotton farmers in south Texas.
Frank graduated from Texas A&M University and took the next step of starting a business. Kunafin is still a family operation today, with 60 employees including entomologists, consultants and field techs.
When the decision is made to incorporate a biological control method, Kunafin entomologists can help design an effective pest control program. They will set up a monitoring schedule and a program tailored to each client’s specific needs.
Chemical control
Chemical control can be used to reduce the population of existing flies prior to beginning a program of releasing parasitic wasps.
Never use chemical control in all of the fly breeding areas when using wasps. Fly pupae are necessary to the wasps’ life cycle.
Chemicals also have limitations, and must be handled, mixed and stored safely and appropriately. If the same chemical is applied repeatedly, resistance becomes a problem.
Junfin says, “Do preventative biological controls, and only use insecticides as a last resort.”
Consumers
Biological control of pests is attractive to consumers. Junfin says, “Consumers have preconceived ideas about animal agriculture, and they can’t fathom that large feedlots and dairies use these kinds of biological controls. Being stewards of the land and incorporating biological pest controls make these industries and their products more appealing to consumers.”
Junfin says, “If we wanted to go totally organic, we couldn’t feed the world, but it’s wonderful to see feedlots and dairies appeasing consumers with better animal care, including biological control. We still need chemicals, but our customers that use chemicals cut that use down tremendously.” 
PHOTO 1: Blaine Junfin releases fly parasites in a feedlot.
PHOTO 2: Fly parasite developing on pupae found in the manure. Photos by Frank Junfin.
Melissa Beck is a freelance writer based in Prescott, Arkansas. Email Melissa Beck.
