Can the Sterile Insect Technique provide a pesticide-free alternative for controlling Diaphorina citri — the vector of devastating Huanglongbing — in residential areas of Southern California?
CDFA Permit No. 4304 approved · 21 residential properties enrolled in East Hemet & Valle Vista · first sterile releases on September 4, 2026 · eight weekly release rounds underway through October.
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The Asian citrus psyllid (ACP; Diaphorina citri) is the major vector of Huanglongbing (HLB) — known as "citrus greening." When an ACP feeds on new citrus growth, it injects the bacterium Candidatus Liberibacter asiaticus (CLas) into the tree's phloem tissue. The bacterium multiplies, blocks nutrient flow, and kills the tree within 3 to 5 years. There is no cure.
HLB has already devastated Florida's citrus industry, which has lost more than 80% of its production since 2010. In 2023–24, California accounted for approximately 79% of U.S. citrus production, valued at $2.55 billion. Infected trees have already been confirmed in Southern California residential areas. Keeping HLB from spreading into commercial groves is an urgent priority.
Current ACP management relies on coordinated area-wide insecticide spraying in commercial groves and the release of an imported parasitoid, Tamarixia radiata, in urban areas. But pesticides contribute to environmental damage, harm beneficial insects and pollinators, and risk creating pesticide-resistant psyllid populations. A species-specific, chemical-free solution is needed.
SIT is a proven biological pest control method already used in California against Mediterranean fruit fly and invasive mosquitoes. This project is the first to adapt SIT for ACP. Large numbers of sterile insects are released to overwhelm wild populations — no chemicals, no harm to natural enemies or pollinators.
Before moving into neighborhoods, sterile releases were tested inside replicated 10′×10′×10′ field cages built over mature lemon trees at UC Riverside Agricultural Operations. Each cage held an established wild ACP population, allowing suppression to be measured against untreated controls across every life stage.
Experiments in 10'×10'×10' field cages at UCR Agricultural Operations established wild ACP populations on mature lemon trees, then applied sterile releases at overflooding ratios (OFR) of 10:1 or 15:1 at doses of 240 or 320 Gy. Populations were measured at predicted F1 and F2 generation peaks using shoot-tip sampling and yellow panel traps.
Building on Year 1, this round used 320 Gy only and compared single releases vs. multiple releases (Weeks 1, 2, and 3) at 10:1 and 15:1 OFRs. This design better mirrors what an operational SIT program would look like in the field — aligning with programs run against other pests like Mediterranean fruit fly.
We are working with homeowners in East Hemet and Valle Vista with citrus trees to take part in a first-of-its-kind pilot. There is no cost, no chemicals, and no work on your part — just a chance to help protect California citrus. Field-cage trials have shown that releasing sterile psyllids can cut the size of the next generation by more than 80%.
Backyard citrus in residential neighborhoods is a persistent reservoir of ACP that threatens commercial groves — and one where coordinated spraying is impractical. Every acre of treated grove in Hemet and Valle Vista sits next to untreated residential citrus. This pilot tests whether that edge can be suppressed without chemical inputs. SIT is a targeted tool, not a replacement for grove management: it is intended alongside parasitoid releases and targeted insecticides, not instead of them.
Released psyllids are reared on curry leaf, a host of ACP that is non-permissive to CLas, so they are disease-free at release. Adult ACP can acquire CLas from infected citrus, although acquisition during the adult stage is substantially less efficient than during the nymphal stage.
At 320 Gy, females are sterile and males are nearly completely sterile. The very small number of F1 offspring that can result from irradiated males are themselves sterile. Adults typically live several weeks. Irradiated does not mean radioactive — the same principle used against Mediterranean fruit fly.
Nothing is sprayed on any property at any point. No residues, no pre-harvest intervals, and no drift concerns at the urban edge.
Because SIT targets reproduction within the same species rather than using an insecticide, it does not create insecticide-resistance selection pressure. Bees, butterflies, lady beetles, Tamarixia, and other natural enemies are unharmed.
Broad-spectrum applications adjacent to an active release site will kill sterile psyllids and confound the results. Where release clusters sit close to treated blocks, advance notice of planned applications lets us schedule releases around them — protecting both the treatment program and the integrity of the pilot data.
Districts and growers cooperating with the pilot receive monitoring data from the release area, advance notice of every release window, and the first open-field evidence on whether SIT can suppress ACP at the residential–commercial interface. To coordinate, contact the project team using the details above.
A phased research program to demonstrate, validate, and recommend SIT for operational ACP management — from insectary to neighborhood. Status as of September 30, 2026.
ACP are reared at UCR on CLas-free Bergera koenigii (curry leaf), sterilized at 320 Gy with the Rad Source RS2400V X-ray irradiator at USDA-APHIS in Salinas, and returned to Hemet in sealed pharmaceutical vials. Sterile adults are marked with fluorescent powder before release. Production now supports the fall 2026 round; spring and fall 2027 rounds follow.
After the CDFA permit (#4304) was issued July 1, 2026, a presentation to the Hemet Citrus Pest Control District Board, door-to-door canvassing, and direct mail enrolled 21 properties in East Hemet and Valle Vista — 11 release and 10 control sites with 42+ citrus trees. ACP activity was confirmed at every site, and the final list was submitted to DPR on September 1, 2026.
The first open-field sterile ACP releases in California history began September 4, 2026, at 11 residential sites — approximately 16,000 sterile adults per release (up to 2,000 per site). Eight weekly releases run through October 22, 2026, with further rounds in spring and fall 2027. To our knowledge, this is the first open-environment field test of SIT for ACP.
ACP activity was confirmed at all sites before releases began. After the final fall release, release and control sites will be monitored monthly through February 2027 using shoot-tip sampling (eggs, nymphs) and yellow panel traps (adults). Population estimates are due to DPR by March 31, 2027.
Because released psyllids carry a fluorescent mark, they can be told apart from wild ACP on traps and foliage. This lets the team measure how far sterile ACP move and how long they persist in neighborhoods where wild psyllids and natural enemies such as Tamarixia radiata are present — data that will inform release densities and overflooding ratios.
A formal recommendation to CDPR, CDFA, and USDA-APHIS on the feasibility of SIT for operational ACP control. The earlier field-cage work behind this pilot is now published in the Journal of Economic Entomology (August 2026). Pilot results will be presented at the California Citrus Conference (October 2026) and the ESA Annual Meeting (2027), and submitted for peer-reviewed publication.
This project operates directly in residential neighborhoods. East Hemet and Valle Vista in Riverside County were selected as the pilot area — communities with significant populations of under-privileged, low-income, and vulnerable residents, including many seniors and children, where backyard citrus sits next to commercial groves. Homeowners who volunteer their properties are the project's most essential partners.
After the CDFA permit was issued on July 1, 2026, outreach moved quickly: a presentation to the Hemet Citrus Pest Control District Board, door-to-door canvassing, and direct mail brought in 21 participating homeowners — above the original goal of 15–20. The first sterile releases followed on September 4, 2026.
All materials are bilingual and written for four audiences: participating homeowners, the general public, commercial growers, and K–8 students. The website at acpsit.com now hosts the outreach materials, a bilingual quarterly newsletter, and an anonymous public opinion questionnaire. Success is measured by homeowners recruited and retained, website visits, downloads, newsletter sign-ups, and survey results. All outreach materials are submitted to DPR for approval before distribution.
Permit to Move and Use Live Plant Pests or Insects or Noxious Weeds. Application submitted December 2025; permit #4304 issued July 1, 2026, valid through July 31, 2028. All movement and release of live psyllids is conducted under its terms.
21 homeowners in East Hemet and Valle Vista signed itemized Property Access Request forms covering repeat visits through March 2028 — 11 release sites and 10 control sites. The final site list was submitted to DPR on September 1, 2026. Participants may withdraw at any time.
The pilot requires roughly 16,000 sterile adults every week during a release round. An operational SIT program serving Southern California would need orders of magnitude more. Dedicated greenhouse infrastructure, and possibly an artificial rearing diet, remain open research questions.
Each release depends on a round trip between UCR and the USDA-APHIS irradiation facility in Salinas, with every shipment and release reported to county agricultural commissioners. This works at research scale; operational programs will need regional irradiation capacity to manage cost and logistics.
Cage trials exclude natural enemies and immigrating wild psyllids. The fall 2026 releases are now testing the central question: how do sterile ACP perform when wild psyllids move freely and Tamarixia radiata is active? Monitoring through February 2027 will give the first answers.
Twenty-one households have opened their yards to the project through March 2028. Keeping that access — through advance notice of every visit, bilingual communication, the quarterly newsletter, and prompt answers at info@acpsit.com — is the most important non-scientific factor in the project's success.
This project was funded by the Department of Pesticide Regulation. The contents may not necessarily reflect the official views and policies of the State of California.