“The sterile males mate with wild females, which then produce no offspring.”

“A flesh eating parasitic fly has spread north through Mexico to within a few hundred miles of the US southern border.”

“The New World screwworm (Cochliomyia hominivorax) lays its eggs in open wounds and in the orifices of live, warm-blooded animals – including, occasionally, humans.”

“Before the 1950s, it was found in the southern states of the US, where cattle infestations caused heavy financial losses for beef producers.”

“During the second half of the 20th century, eradication efforts pushed it out of North and Central America.”

“In the past few years, however, screwworm control has unravelled, with cases spiking across Central America.”

“The fly has now spread north through Mexico, reaching two Mexican states – Tamaulipas and Nuevo Leon – that share a border with Texas.”

“The method that was used to eradicate the fly is known as the sterile insect technique (SIT).”

“SIT involves breeding vast numbers of a target species, sterilising them, usually with radiation, and then releasing the males.”

“SIT has been used many times on a vast number of pests over the past 80 years – with mixed results.”

“The eradication of screwworm from the US, Mexico and central America was its greatest success.”

“The natural range of the New World screwworm fly extends from the southern states of the USA through Central America and the Caribbean Islands to northern Chile, Argentina and Uruguay.”

“In North America, the fly used to spread north and west each summer from its overwintering areas near the US-Mexican border.”

“In 1935, during a screwworm epidemic, there were approximately 230,000 cases in livestock and 55 in humans in the state of Texas.”

“Female screwworm lay batches of 200-300 eggs in open wounds and orifices.”

“Large-scale SIT for New World screwworm started in Florida in 1957-59 and was gradually rolled out to the west.”

“Effective control by the US was achieved in 1966.”

“Subsequently, using rearing facilities in Mexico, the fly was pushed back through Central America and was held at a barrier at the Darien Gap in Panama using continuous release and surveillance.”

“In the summer of 2016, screwworm infestation was identified in deer in the Florida Keys.”

“The recent breakdown of screwworm control has seen thousands of cases confirmed in animals and humans across Panama, Costa Rica, Nicaragua, Honduras and Mexico.”

“The insect’s continuing northward spread now raises the risk of a costly US reinvasion.”

“The US Department of Agriculture estimates that an outbreak in Texas could cost livestock producers more than US$700 million (£526 million) per year.”

“Maintaining barriers, rearing facilities and surveillance operations are expensive. US federal budget cuts, along with reduced foreign aid, hit screwworm control programmes in Central America and weakened surveillance.”

“The UN’s Food and Agriculture Organization’s (FAO) global health security programme, with responsibility for transboundary animal disease management, reduced its screwworm surveillance as US funding was withdrawn in March 2025.”

“Loss of control over the illegal movement of cattle, lacking veterinary inspections, may also have been a contributing factor.”

“In many countries there has been an ongoing loss of expertise as experienced veterinary entomologists have retired and not been replaced.”

“Traditional applied entomology has been viewed as dated in the face of, for example, modern molecular and genetic approaches to the identification of species.”

“The rearing facilities for sterile insects in Mexico were shut down after screwworm was pushed out of North and Central America in the latter half of the 20th century.”

“However, refurbishment is currently underway to allow them to restart producing sterile flies by summer 2026.”

“A new facility at Moore Airbase in Edin삶s being constructed to support sterile insect production.”

“The sterile insect technique (SIT) requires strict temperature control to maintain insect viability.”