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The sterile insect technique (SIT) has long provided an eco-friendly, sustainable tool for pest suppression and eradication by disrupting reproductive cycles. By releasing mass-reared, irradiated males into target environments, SIT causes wild females to lay non-viable eggs, gradually collapsing pest populations.
Because sterile insects cannot produce larvae or pose a risk to human and animal health, it’s being looked at with new enhancements for both the New World screwworm (Cochliomyia hominivorax, or NWS), as well as for Anopheles spp. mosquitoes.
Research on malaria mosqitoes
The mosquito study is especially noteworthy because SIT has been successful with Aedes species such as the Asian tiger mosquito (A. albopictus) and the yellow fever mosquito (A. aegypti) because the females of these species tend to be larger than the males, and thus easier to automatically sort. By contrast, both sexes in Anopheles spp. tend to be similar in size.
As Dr. Dongjing Zhang, of Sun Yat-Sen University in Guangzhou, China, a co-author of a new mosquito study on the subject, explains in an article from the Entomological Society of America’s online publication, Entomology Today: “Physical sex sorting relying on pupal size disparity works well for Aedes mosquitoes, yet Anopheles males and females show negligible differences in body size and pupation timing, rendering mechanical sex separation impractical. Manual sorting is extremely slow and cannot support large-scale field releases. Our approach leverages a fundamental biological distinction: Only female mosquitoes take bloodmeals, whereas males never feed on blood.”
Per the article, “when a spiked bloodmeal is offered, the females feed and drop like proverbial flies, while males ignore the blood and survive. The technique does not kill quite enough females to meet the threshold of less than 1 percent for direct release of mosquitoes, but it makes manually sorting out the few survivors a breeze.”
After testing 11 candidate compounds on Aedes albopictus, researchers verified the protocol’s success in the Asian malaria mosquito (Anopheles stephensi). The team hopes that further testing to streamline the process can clear a path for operational-scale Anopheles SIT programs.
Research on containing NWS
To maintain suppression and prevent spread of NWS, the U.S. Department of Agriculture (USDA) continuously monitors screwworm detections and adjusts sterile fly release patterns using two delivery methods:
- Aerial dispersal: As the USDA notes on its website, “most sterile flies are released by air. After pupae hatch at a release facility, adult flies are loaded into chambers on an aircraft and dispersed through release tubes over the target area. Aerial release provides steady, uniform coverage across large and hard‑to‑reach regions.”
- Ground Release: This method, as described by the USDA, is used “when sterile flies need to be deployed quickly or in areas beyond typical aerial coverage. Flies can be released from trucks, which disperse them much like aerial operations, or from ground release chambers — crates placed in targeted spots where pupae hatch and flies emerge, providing highly localized support where needed.”
To distinguish sterile flies from wild populations during trapping and public surveillance, the USDA dyes pupae with a fluorescent marker visible under ultraviolet (UV) light, and occasionally to the naked eye.
Current NWS strategies
At press time, the USDA and Panama’s Ministry of Agriculture Development (MIDA) jointly manage North America’s sole operational NWS sterile fly production facility through the Commission for the Eradication and Prevention of Screwworm (COPEG). Located in Pacora, Panama, the facility generates over 100 million pupae per week. To meet rising demand, the USDA is expanding domestic infrastructure and investing in new sterile fly production capacity.
Operationally, NWS pupae are exposed to gamma radiation to sterilize adult flies without reducing their survival or mating competitiveness. Because female NWS mate only once, releasing these flies leads directly to population decline.
To streamline this process, the USDA is developing NovoFly, a novel, trademarked, male-only strain designed to maximize efficiency by increasing the proportion of sterile males produced for release. While NovoFly is not yet active in field operations, regulatory reviews and field evaluations are underway.
