The UC Riverside Department of Entomology is evaluating the Sterile Insect Technique (SIT) as a tool to suppress populations of Asian citrus psyllid (ACP) — the insect vector of Huanglongbing (HLB), the bacterium-caused disease responsible for citrus greening. The approach involves rearing large numbers of ACP under controlled laboratory conditions, sterilizing them, and releasing them into the field. Because sterile adults retain the ability to mate but cannot produce viable offspring, repeated releases progressively reduce the reproductive output of wild populations.
The ACP-SIT Pilot Program has completed its first operational quarter, marking a series of foundational milestones: regulatory approval of the first-ever California permit to release irradiated Asian citrus psyllids, production and distribution of bilingual outreach materials, successful enrollment of 21 residential properties in East Hemet and Valle Vista, and the first open-field sterile releases on September 4, 2026. This newsletter summarizes the key activities and outcomes of that period.
CDFA Permit Procurement
A central prerequisite for any open-field SIT program using a regulated plant pest is state regulatory authorization. In December 2025, the project team submitted an application to the California Department of Food and Agriculture (CDFA) for a Plant Pest Permit authorizing the movement and release of live, irradiated Diaphorina citri (Asian citrus psyllid, ACP) in Riverside County.
The application covered three key activities: (1) transport of live adult ACP from the mass-rearing colony at UC Riverside to the USDA-APHIS-PPQ sterilization facility in Salinas, CA (Monterey County); (2) irradiation of those psyllids at a dose of 320 Gray using the facility's X-ray machine; and (3) open-field release of sterile adults at enrolled residential properties in Hemet and Valle Vista, Riverside County.
CDFA issued the permit on July 1, 2026.
"The first permit of its kind in California to authorize open-field release of irradiated Asian citrus psyllids — a necessary milestone for any residential SIT program."
Outreach Materials
A suite of bilingual outreach materials was developed and deployed to support homeowner recruitment and to communicate the science of SIT to a wide audience. Materials were produced in English and Spanish, using conventions familiar to Southern California Spanish speakers, and targeted at four groups: participating homeowners, growers, general public and K–12 school children.
Residential Site Recruitment
Recruitment focused on residential neighborhoods in Hemet and Valle Vista, Riverside County, where backyard citrus trees represent a persistent ACP reservoir adjacent to commercial citrus blocks. Outreach began in August 2026 with a presentation to the Hemet Citrus Pest Control District followed by door-to-door canvassing, and/or direct mail.
Residents were invited to enrol voluntarily, at no cost, and with no obligation to be home during visits. Each participant signed an itemized Property Access Request form specifying exactly which activities they authorized — releases, trap hanging, tap samples, leaf collection, tree tagging, and photography.
ACP activity was confirmed at all sites and a final list of 21 participants was submitted to DPR on September 1, 2026.
First Open-Field Releases
The first open-field sterile ACP releases in California history took place on September 4, 2026. Across 11 residential sites, approximately 16,000 sterile adult ACP were released onto citrus trees (maximum 2,000 per site).
Weekly releases were conducted at each property through September and will continue into October, completing the full eight-release fall 2026 window. Similar release windows will follow in spring and fall 2027.
ACP reared at UCR on Candidatus Liberibacter asiaticus (CLas)-free Bergera koenigii (curry leaf) were sterilized at the USDA-APHIS facility in Salinas, then transported to Hemet and released directly from pharmaceutical vials onto enrolled citrus trees. Sterile psyllids are marked with a pink fluorescent powder to allow subsequent discrimination from wild psyllids.
Key Milestones
What Comes Next
- Three additional weekly sterile releases in October — Oct 8, 15 & 22 — completing the full eight-release fall 2026 window at all 11 Hemet release sites.
- Continued notification of Riverside and Monterey County Agricultural Commissioners for each shipment and release, as required by Permit No. 4304.
- Post-fall monitoring through winter: monthly ACP population surveys at all 21 sites to measure the effect of the eight September–October releases.
- Spring 2027 release window: eight additional weekly releases timed to the peak ACP reproductive flush period.
- Ongoing community outreach, including Spanish-language engagement at enrolled sites and grower coordination with the Hemet CPCD.
outreach materials — and the latest from Hemet.