Earlier this month, the USDA confirmed the first U.S. cases of New World screwworm in sixty years, found in cattle in South Texas. The screwworm is a parasitic blowfly whose larvae feed on the living tissue of warm-blooded hosts including livestock, wildlife, pets, and occasionally people, and its return has ranchers and officials on alert.
You may have paused at seeing the response strategy in the news: the USDA is releasing millions of sterilized screwworm flies across the affected area. While it may sound strange, this isn’t a new experimental technology. It is known as “Sterile Insect Technique” (SIT), a pest management approach that has been in use for decades, and the previous eradication of New World screwworm was actually the first large-scale field success of the technology.
The premise of SIT is straightforward: large numbers of sterilized males are released into the outbreak area, and wild females pair with them and lay eggs which will never hatch. If releases are sustained, each generation shrinks and the population plummets. Success depends on maintaining a high ratio of sterile to wild flies, and on trapping surveys throughout to track the population and confirm the program is working.
USDA scientist Alfred Baumhover previously recounted his experiences developing and proving this method in the field in an article in Florida Entomologist. The first full test was performed in 1954 when researchers targeted a wild screwworm population on the Caribbean island of Curaçao, and within months the screwworm was gone. After this success, and under significant pressure from US livestock owners, the approach was quickly scaled up into a much larger program, and eradication across Florida and the Southeastern US was declared in 1959.
Baumhover also noted in his account that where treatment of infested animals stopped too soon, before the fly was completely gone, surviving larvae matured into new fertile flies and set the program back. This is a key lesson in integrated pest management: even proven tools require sustained monitoring, treatment, and cooperation.
The fly Baumhover studied in 1954 is the same one Texas faces now, and the method he helped prove is still the backbone of the response. If you want to understand the science behind the current headlines, his first-hand account is a good place to start.
Read the original article: Baumhover, A.H. (2002). A Personal Account of Developing the Sterile Insect Technique to Eradicate the Screwworm from Curaçao, Florida and the Southeastern United States. Florida Entomologist 85(4): 666–673.