There are some basic questions that must be answered to determine the probable effectiveness of the Sterile Insect Technique with a given species and in a given area before it is implemented. Those questions include:

• Is there an effective and reasonable economic method of mass rearing the target insect?
• Can the released insect rapidly disperse through the wild population?
• Will sterilization affect mating competitiveness? (i.e., will sterile males be able to compete with native males and win mates?)
• Is it possible to achieve effective over-flooding ratios with sterile insects over the wild pest population?

Once insects are reared and sterilized, they are ready for release. Before a large-scale release, an evaluation will be conducted. Things to consider with an evaluation release include location, time of release, method of release, number of insects needed achieve high over-flooding ratios and methods of evaluating effectiveness.

Sterilized insects may be released by hand, in a small evaluation to study how they live and how they move. Another option is ground release by truck. In larger evaluations or operational programs, insects may be released by aircraft.

The number of sterile insects necessary to release to ensure effective pest suppression varies by species. For the Light Brown Apple Moth, we are going to start with a release rate to achieve an over-flooding ratio of ten sterile insects to one wild/fertile insect. This figure is based on research in a vineyard system in New Zealand that demonstrated this would be an appropriate ratio to test in California. The total number of sterile insects needed for release is based on several factors including the size of the pest population, crop type, climate and competitiveness of the sterile insect.

There are limits on the number of insects that can realistically be released at one time, so there are generally multiple sterile insect releases in a week, until stable over-flooding rations are achieved. With continued releases, a reduction of the density of pest population is achieved over the course of the season. Monitoring traps are placed at various locations in and around the release area to evaluate the effectiveness of a SIT program. The traps are used to determine if effective over-flooding of sterile to wild pest insect ratios are achieved, what the presence and size of the pest population is, and to track other aspects of SIT program operations, such as insect movement (including how far they go and which directions they travel). These types of information are all used to help refine the SIT to make the program more effective.

There is much more information to share about the SIT—including more answers to commonly asked questions—so keep checking this blog.

Gregory S. Simmons, Ph.D.
APHIS-PPQ-CPHST Light Brown Apple Moth Coordinator
United States Department of Agriculture