Last Modified: August 06, 2026
Sterile NWS fly on a leaf

The sterile insect technique (SIT) is a sustainable, eco-friendly way to control insect pests by disrupting their ability to reproduce. USDA uses SIT to control and eradicate New World screwworm (NWS). Sterile flies are safe—because they can’t produce larvae, they cannot cause harm. They pose no risk to animals or people.

Proven Effectiveness of SIT

SIT has been studied extensively over decades and consistently proven to work. It helped eradicate NWS from the United States in 1966 and eliminate a small outbreak in the Florida Keys in 2017. As one of the most effective tools for controlling and eradicating NWS, SIT remains a cornerstone of USDA's response strategy.

Advancements in Sterile Insect Technique

USDA is working on a significant enhancement to its long‑standing and successful Sterile Insect Technique program. The new NovoFly™ male‑only strain is designed to improve efficiency by increasing the number of sterile male flies available for release. NovoFly™ is not currently used in SIT operations; USDA is sharing information now so stakeholders can better understand the technology, how it works, and how it may support future NWS eradication efforts once regulatory reviews and field evaluations are complete.

Read our NovoFly™ Questions & Answers 

How SIT Works

  1. In specialized facilities, NWS pupae are exposed to gamma radiation to produce sterile flies—without affecting their ability to survive or mate.
  2. Sterile flies are released into the environment.
  3. Wild NWS flies mate with the sterile flies. Their resulting eggs don't hatch.

  4. Because female NWS flies mate just once, the pest population gradually dies out.

Sterile Fly Production

USDA and Panama’s Ministry of Agriculture Development (MIDA) jointly manage and fund the only NWS sterile fly production facility currently in operation in North America through the Commission for the Eradication and Prevention of Screwworm (COPEG). Located in Pacora, Panama, this facility can generate more than 100 million pupae per week. To meet increased demand, USDA is expanding our domestic response capacity by investing in new and existing sterile fly infrastructure.
 
 

How Sterile Flies Are Released

Sterile flies are released in and around infested areas to increase the likelihood that wild NWS flies will mate with them. USDA continuously monitors new detections and adjusts release patterns to maintain suppression and prevent spread.

Aerial Dispersal

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

Ground release 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.
New World screwworm sterile fly ground release chambers hanging from trees in an arid landscape

Public Awareness and Monitoring

Surveillance continues in areas where sterile flies are released, so sterile NWS flies may appear in traps or be reported by the public. To distinguish them from wild flies, USDA dyes the pupae with a fluorescent marker that carries over to the adults. The dye—visible under UV light and sometimes to the naked eye—allows officials to quickly identify sterile flies and rule them out as a threat.

You Don’t Need To Look for NWS Flies

Many fly species look alike, and even a true NWS fly could be a harmless sterile one released for eradication efforts. So there’s no need to watch for flies themselves. Instead of looking for flies, focus on protecting your animals:

Download Printable Factsheets About SIT

Sterile Insect Technique: A Proven Tool for Fighting New World Screwworm
Sterile Fly Release Methods for Controlling Screwworm