Last October, a press release from the Florida Department of Agriculture confirmed the presence of screwworms in deer on a wildlife refuge. This local infestation of New World screwworms caused a good bit of alarm for livestock producers as well as wildlife enthusiasts at the very southern end of Florida.
Around these parts, only the very senior ranchers and outdoorsmen may remember the screwworm, also called blowflies, when it was a problem here.
While the adult fly shares many characteristics with the common house fly, the eggs they lay and the damage they do vary tremendously. While most of us correctly identify more common fly larvae (maggots) as found in dead carcasses, the screwworm’s larvae can feed on living tissue and cause tremendous damage, even to the point of death.
Eggs are laid by the flies in lesions or other wounds a host animal may have. Apart from traumatic injuries, scratches from thorns or barbed wire could be enough to provide the opening. Unlike most other fly maggots, these maggots attack and consume healthy living tissue along with decaying tissue.
The scientific name of the screwworm is Cochliomyia hominivorax. Cochliomyia is a genus in the family Calliphoridae, known as blowflies. The second part of the name, hominivorax, literally translates to “man-eating”.
The United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed the presence of New World screwworm in Key deer from a wildlife refuge in Big Pine Key, Florida. Big Pine Key is one island off the coast of mainland Florida that covers 10 square miles. Driving Interstate 1 to Key West, it would have been one of the larger islands the highway would have crossed.
The screwworms that our parents and grandparents remember was officially eliminated in the US in 1966. Its elimination is still a huge entomological success story that includes the use of atomic energy.
Scientists as early as the 1930’s looked for a better solution than treating the pests topically after entry into hosts via skin wounds, as was the common procedure.
Though World War II’s pressing entomological needs intervened, a scientist by the name of Edward F. Kipling never gave up thinking about using genetic means to control screwworms. In 1946, he was named chief of the “Insects Affecting Man and Animals Division” of USDA’s Bureau of Entomology and Plant Quarantine. Four years later, a colleague recommended to Knipling a book which discussed use of
radiation to alter the genetic material of insects. Knipling immediately began a correspondence with the author exploring the possible use of radiation to sterilize screwworms.
Convinced that the approach could work, Knipling reordered priorities to provide funding for scientists to carry out tests at Kerrville, Texas. They secured the cooperation of a nearby U.S. Army medical unit with suitable x-ray equipment. In just 6 months, it was handily demonstrated that 2,500 to 5,000 roentgens of x-rays would sterilize screwworm pupae without disrupting their adult mating behavior.
Knipling’s theory was simple: Fertile females would mate with sterilized males mass-reared in insectaries and released into infested areas. With offspring resulting only from matings with native, unsterilized males, the screwworm population would gradually become insignificant and perhaps disappear.
But could it really work? First, a field test on Sanibel, another Florida key island that is 20-square-miles, confirmed the theory. Though encouraged, scientists knew that a larger test was needed to verify those early findings. By chance, a routine request from a veterinarian from Curacao, Netherlands Antilles, (located in the Caribbean next to modern day Aruba) alerted them to the screwworm’s presence on the 170-square-mile island. The Dutch government was eager to assist in its elimination.
So a thousand sterile flies per square mile were released each week by airplane. And by the end of the nine week period, very few egg cases were to be found and all were sterile!
The speed with which screwworm eradication was achieved on this remote Caribbean island demonstrated the great potential of this control method. Since then, strategic deployment of sterile flies has been used effectively in the US and most recently, northern Africa–to protect vast areas from the horrific screwworm’s predations.
Prior to this control strategy, this obnoxious fly larvae caused immeasurable suffering and losses in livestock, wildlife, and even human populations the world over.
So what is to come of this recent outbreak? We do know how to control it. I haven’t read where it came from… though others at higher levels may very well have their suspicions.
Should it cause alarm for our corner of the world in East Texas? I wouldn’t go running down the road screaming the sky is falling.
On Monday, Jan. 16 at 6:30 pm, the Angelina County Extension Office will be hosting a Livestock Health Seminar at their office next to the Farmers Market in Lufkin. Featured speaker is Dr. Tom Hairgrove, an Associate Professor and Extension Specialist in the Department of Animal Science at Texas A&M University. He will be discussing the new Veterinarian Feed Directive and other current livestock health topics.
