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?
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. California now produces approximately 79% of all U.S. citrus — a $2.55 billion industry. 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 looking for homeowners in Hemet and San Jacinto 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 San Jacinto 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 plant that cannot carry the HLB bacterium. As adults they cannot effectively acquire or transmit the pathogen.
A 320 Gy X-ray dose gives 100% F1 sterility. They mate, but produce no viable offspring, and live only a few 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.
Only ACP is affected. Bees, butterflies, lady beetles, Tamarixia, and other natural enemies are unharmed — and repeated use creates no resistance pressure.
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.
Scale up ACP mass-rearing at UCR on Bergera koenigii. Validate transport and irradiation protocols with USDA-APHIS, Salinas. Ensure sufficient sterile adult production for 8 weekly releases at each of three field rounds.
Engage 15–20 residential properties in Hemet and San Jacinto through community meetings and HOA outreach. Confirm active ACP populations and citrus host trees at each site. Secure all site permissions before first releases (August 2026).
Conduct three rounds of 8 weekly sterile ACP releases at residential sites (fall 2026, spring 2027, fall 2027). This is the first open-environment test of ACP SIT — a critical step beyond closed cage trials into real-world neighborhood conditions.
Monthly monitoring of wild ACP populations at release and control sites using degree-day models, destructive shoot-tip sampling (eggs, nymphs), and yellow panel trap counts for adults. Assess suppression across all life stages over multiple generations.
Measure how far sterile ACP disperse and how long they persist in open residential environments with natural enemies present. Data will inform release densities, spacing, and overflooding ratios for operational programs across Southern California.
Deliver a formal recommendation to CDPR, CDFA, and USDA-APHIS on the feasibility of deploying SIT for operational ACP control. Findings published in peer-reviewed journals and presented to the Citrus Research Board and ESA annual meeting.
This project operates directly in residential neighborhoods. The cities of Hemet and San Jacinto in Riverside County Citrus Pest Control District No. 3 were selected as the pilot area — communities with significant populations of under-privileged, low-income, and vulnerable residents, including high numbers of seniors and children. Homeowners who volunteer their properties will be the project's most essential partners.
The outreach plan spans 12 tasks across all phases of the project. Materials will be designed for multiple audiences including the general public, homeowners, commercial growers, and K5–8 children. The project website — live by September 30, 2026 — will provide a freely available, continually updated public resource including a Q&A space and downloadable materials.
Survey instruments before and after each meeting will measure changes in community understanding of SIT and ACP. Measures of success include number of homeowners recruited, website visitor counts, material downloads, and post-meeting 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 1, 2025. Approved by CDFA as permit #4304; all releases and movement of live psyllids are conducted under its terms.
Permission to access 15–20 residences repeatedly over a 2-year period. Garnered through meetings with local groups and HOAs. All site permissions acquired by end of August 2026. If insufficient sites are found within Hemet and San Jacinto, additional areas such as Mentone and Yucaipa (San Bernardino County) may be explored.
UCR's current insectary produces over 40,000 adult ACP per month. An operational SIT program serving Southern California would require orders of magnitude more. Investment in dedicated greenhouse infrastructure and potentially an artificial diet for rearing are open research questions.
Overnight transport of sealed psyllid vials between UCR and the USDA-APHIS irradiation facility in Salinas is feasible for research-scale releases. Operational programs will require co-located or regionally distributed X-ray irradiation infrastructure to manage costs and logistics at scale.
Cage experiments are closed systems — they exclude natural enemies and prevent wild ACP immigration. The central, unanswered question this pilot project addresses: how will sterile ACP perform when wild psyllids can freely enter and leave, and Tamarixia radiata biological control is active in the area?
Maintaining access to 15–20 residential properties over two years is the single most important non-scientific factor in the project's success. Transparent communication, advance notice of every visit, and ongoing relationship-building with homeowners and HOAs underpin everything else.
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