New world screwworm (Diptera: Calliphoridae): past, present and future.

The New World screwworm (NWS), Cochliomyia hominivorax (Coquerel), is one of the most important parasites of livestock and wildlife in the Americas. Research conducted during the last 100 yr has formed the foundation of the most successful insect control program in the world: the NWS eradication program. The program eradicated NWS from North and Central America and established a biological barrier at the Isthmus of Panama in 2004 using the Sterile Insect Technique (SIT). Except for a brief incursion in the Florida Keys in 2016, the last case of NWS in the United States was in 1982. Since the eradication of NWS from the United States, livestock husbandry practices have changed dramatically, leaving the livestock industry in the southern half of the United States vulnerable to NWS. Research during the 1930s, 1940s, and 1950s established the foundation upon which the eradication program was built: NWS mass production, sterilization, and dispersal. More recent research has improved efficiency and reduced program costs, but the backbone remains intact. A program to eradicate NWS from Jamaica initiated in 1998 was declared a failure in 2009. In 2023, the Panamanian barrier was breached and NWS quickly recolonized much of its historical range through Central America and Mexico. It is essential to identify the causes of these failures to avoid future lapses and improve effectiveness of the eradication program. As was the case with previous program lapses in 1974 and 1986, unbiased external review is called for to protect livestock producers, wildlife, and the public trust.