Sterile Flies Help With NWS Prevention

REDFIELD, Iowa (DTN) -- USDA's Animal and Plant Health Inspection Service (APHIS) is adjusting its New World screwworm (NWS) sterile fly dispersal strategy to help keep the pest out of the U.S., according to a news release from APHIS.

The previous biological barrier was in Panama, but with the recent spread of NWS cases farther north into Mexico, APHIS is shifting its dispersal efforts to the northernmost point of the outbreak in Mexico.

NWS ERADICATION EFFORTS

Eradicating NWS is only possible through the sterile insect technique. Iowa's state entomologist, Robin Pruisner, told DTN the logistics and efficacy of releasing sterile male NWS works well, and the process has been used previously in the U.S. to eradicate the problem.

"The sterile insect technique (SIT) involves sterilizing millions of male insects using ionizing radiation before releasing them into the wild to mate with wild females," she said. "As no offspring can be produced, the SIT leads to a drastic reduction in the wild populations of the disease carrier while minimizing the use of pesticides."

Since the female fly only mates once, this helps eliminate the population.

APHIS said this remains the most effective strategy. The agency has identified two locations for sterile fly dispersal centers in Mexico. Dispersal centers outside of Mexico will continue to ensure program continuity.

"By adjusting dispersal locations, we ensure the greatest number of sterile flies are released in the critical areas," the APHIS news release stated.

While sterile fly dispersal will shift north, APHIS will continue to work with Nicaragua, Honduras and regional partners to support surveillance, animal health outreach and early detection efforts.

NWS CAN CAUSE ANIMAL DEATH

NWS are fly larvae that infest living tissue of warm-blooded animals, causing infection. According to APHIS, these maggots will burrow into a wound, feeding as they go, doing extensive damage by tearing the host's tissue with sharp mouth hooks. The wound becomes larger and deeper. NWS can cause serious, even deadly damage to the animal.

The adult screwworm flies are about the size of a common housefly with orange eyes, a metallic blue or green body, and three dark stripes along their backs.

Affected mammals and birds show signs of irritated behavior, head shaking, smell of decay, evidence of fly strike, and presence of fly larvae in wounds.

When the first case was found in Mexico in December 2024, imports of live cattle from Mexico to the U.S. were halted. Imports resumed in February with a strict animal health protocol prior to entry.

Jennifer Carrico can be reached at jennifer.carrico@dtn.com

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