Sterile insect technique vs Wolbachia
Two ways to make male mosquitoes whose matings produce no offspring. Same goal, different methods.
Both methods release male mosquitoes, which don't bite, and both stop the eggs of the wild females they mate with from hatching. The sterile insect technique (SIT) sterilizes the males with radiation, while Wolbachia males carry a common insect bacterium that has the same effect on eggs. Both have peer-reviewed US results; they differ mainly in how the males are made, how they're regulated and how stray females are handled.
How Wolbachia males work
Wolbachia is a bacterium found naturally in many insects. Programs use it to make males that wild females can't breed with.
The CDC says about 6 in 10 insect species carry Wolbachia, including butterflies, bees and beetles.¹ Labs infect a mosquito line with a strain the local females don't carry. When a male with that strain mates with a female without it, her eggs don't hatch. Scientists call this the incompatible insect technique (IIT).
The males are raised, sorted so only males are kept, and released, often several times a week. The CDC states that mosquitoes with Wolbachia are not genetically modified.¹
1. CDC, "Mosquitoes with Wolbachia," cdc.gov, May 14, 2024, https://www.cdc.gov/mosquitoes/mosquito-control/mosquitoes-with-wolbachia.html
How irradiated sterile males work
SMF uses the sterile insect technique: biological control, with nothing added to the mosquito, and X-rays do the sterilizing. Like Wolbachia, it affects only the species released, so it's safe for people, pets, pollinators and the environment.
Four steps to fewer mosquitoes
How each is regulated
The two methods sit in different places in US rules, because one carries a bacterium and the other carries nothing.
Wolbachia. The CDC says the EPA regulates mosquitoes with Wolbachia, an experimental use permit is needed before field trials, and state and local authorities must also approve releases.¹ In November 2017 the EPA registered ZAP Males, Asian tiger mosquito males carrying a Wolbachia strain, as a biopesticide (reg. no. 89668-4). The first registration covered Washington, DC and 20 states; a December 2023 amendment removed that geographic limit.² EPA rules exempt most biological control agents from pesticide law but not microorganisms such as bacteria, which is why a Wolbachia product is registered.³
Irradiation. The CDC describes SIT as a non-patented method that uses radiation to sterilize males, and states that irradiated mosquitoes "are not genetically modified and are not regulated by the Environmental Protection Agency."⁴
1. CDC, "Mosquitoes with Wolbachia," May 14, 2024. 2. EPA, "EPA registers the Wolbachia ZAP strain in live male Asian tiger mosquitoes," November 2017, https://www.epa.gov/pesticides/epa-registers-wolbachia-zap-strain-live-male-asian-tiger-mosquitoes; amended label, December 5, 2023, https://www3.epa.gov/pesticides/chem_search/ppls/089668-00004-20231205.pdf 3. 40 CFR 152.20(a), https://www.ecfr.gov/current/title-40/chapter-I/subchapter-E/part-152/subpart-B/section-152.20 4. CDC, "Irradiated mosquitoes," May 14, 2024, https://www.cdc.gov/mosquitoes/mosquito-control/irradiated-mosquitoes.html
The evidence for each method
Both methods have peer-reviewed US results. These are public programs' results, labeled by method, not SMF's.
What public programs have measured
Evidence for the method, not SMF's own results.
1. CDC and Harris County Public Health, Wolbachia method. Lozano et al., PLOS Neglected Tropical Diseases, 2022. 2. Lee County Mosquito Control District, Captiva Island, Florida. Phase 1 only. Morreale et al., PLOS Neglected Tropical Diseases, 2025. 3. West Valley Mosquito and Vector Control District, California, 2024. Birhanie et al., Insects, 2025.
See the researchTwo more results help complete the picture. In Fresno, California, Wolbachia males cut female mosquitoes 95.5% at peak season (related method); a later published critique questioned parts of the analysis.¹ And on two river islands in Guangzhou, China, a program that combined both methods, Wolbachia males given a low X-ray dose, reported near-complete suppression of the Asian tiger mosquito over two years.² More detail is in our published results.
1. Crawford et al., Nature Biotechnology, 2020, doi:10.1038/s41587-020-0471-x; critique: Bouyer, Maiga and Vreysen, Nature Biotechnology, 2022. 2. Zheng et al., Nature 572: 56-61, 2019, about 200 million males over 32.5 ha, 2016 to 2017, doi:10.1038/s41586-019-1407-9 (combined method).
The female question
Only females bite, so every sterile-male program removes them before release. What happens to a stray female differs by method.
With Wolbachia. A female carrying the release strain can breed with the released males, because they're compatible. If enough slip through, the strain can spread into the wild population, and over time releases work less well. Researchers have studied a low radiation dose as a backstop that sterilizes any stray females, which is what the Guangzhou program did.¹ ²
With irradiation. Any female that gets past sorting goes through the X-ray step too. In published dose studies, female Aedes are generally more sensitive to radiation than males.³ She can still bite, though, so sorting precision matters. Lee County's public program set a quality-control limit of 0.2% females or less.⁴
At SMF. Females are removed first, using AI vision from our technology partner, Senecio. X-ray sterilization is the last step before the males leave our facility. We hold females to 0.2% or less, and because the X-ray step treats the whole batch, any female that slips through is sterile too.
1. Zhang D, et al., PLOS ONE 10(8): e0135194, 2015, https://pmc.ncbi.nlm.nih.gov/articles/PMC4529199/ 2. Zheng et al., Nature, 2019. 3. Yamada et al., Parasites & Vectors, 2019, doi:10.1186/s13071-019-3698-y; Balestrino et al., Journal of Medical Entomology 47(4), 2010. 4. Morreale et al., PLOS Neglected Tropical Diseases, 2025.
Side by side
| Compared on | Irradiation SIT (SMF's method) | Wolbachia (IIT) |
|---|---|---|
| How males are made | Females removed, then X-rays sterilize the males | Males carry a Wolbachia strain the local females lack |
| Anything added to the mosquito | Nothing | A bacterium |
| Genetically modified | No¹ | No² |
| Do the released males bite | No | No |
| US regulation | CDC: not regulated by the EPA¹ | Registered by the EPA as a biopesticide; state and local approval² ³ |
| Peer-reviewed US results | Lee County, FL; West Valley, CA | Harris County, TX; Fresno, CA; South Miami, FL |
| A stray female | Exposed to the X-ray step; can still bite | Could pass the strain on if she breeds |
| Species affected | Only the species released | Only the species released |
1. CDC, "Irradiated mosquitoes," cdc.gov, May 14, 2024. 2. CDC, "Mosquitoes with Wolbachia," 2024. 3. EPA ZAP Males registration, 2017.
When Wolbachia is the right choice
It's a proven, related method, and in the right setting it's a sound pick.
- A provider already serves your area. Providers are few. If one covers your neighborhood, the evidence behind the method is strong.
- Your agency prefers a registered product. Some public programs want an EPA-registered pesticide label behind every tool. A Wolbachia product has one.
- Your district has already chosen it. Sacramento-Yolo in California picked Wolbachia males for its programs. Matching the local public program keeps things simple.
Using them together
The two methods aren't rivals. Researchers combine them, as in Guangzhou, and both work best with the basics in place.
On one property, you'd normally run one release program for a species and pair it with source reduction: tipping out standing water and treating water that can't be drained. Comparing other options? See sterile males vs genetically modified mosquitoes or vs bats, birds and mosquitofish, or Compare all options. The science behind SIT is on the science page, and safety detail on our safety page.
FAQ
CDC, "Mosquitoes with Wolbachia," 2024. Lozano et al., PLOS NTD, 2022.
Is Wolbachia the same as the sterile insect technique?
Not quite. Both release males whose matings with wild females produce eggs that don't hatch. SIT sterilizes the males with radiation. Wolbachia males aren't sterile on their own; they carry a bacterium that makes them incompatible with local females.
Are Wolbachia mosquitoes genetically modified?
No. The CDC states that mosquitoes with Wolbachia are not genetically modified. Irradiated mosquitoes aren't either.
Is Wolbachia safe for humans?
The CDC says Wolbachia bacteria cannot make people or animals sick, and that there is no data suggesting they harm people, animals or the environment. The released males don't bite.
Which works better, SIT or Wolbachia?
Both have strong published results, and outcomes depend more on release design than on method. Programs did best where few wild females could fly in from untreated areas.
Have Wolbachia mosquitoes been released in Texas?
Yes. In 2019, Wolbachia males were released near Houston under an EPA experimental use permit, and the CDC and Harris County Public Health evaluated the results independently.
Other comparisons: Barrier sprayingFoggingMisting systemsLarvicides and dunksCO2 mosquito trapsMosquito trapsBug zappersRepellents and devicesGenetically modified mosquitoesBats, birds and mosquitofishNatural yard treatments Compare all options
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