California Psyllids Carrying HLB Bacterium in Groves

Tacy Callies California Corner, Psyllids

Asian citrus psyllid
(Photo credit: UC Regents)

An ongoing study in coastal Southern California citrus groves has found that just over 3.5% of Asian citrus psyllids (ACP) tested are carrying the bacterium that can cause HLB. ACP is the insect vector of HLB. Thus far, 138 of 3,000 adult ACP collected from 15 commercial citrus sites had some level of the bacterium present.

The results were reported by researchers from University of California (UC) Agriculture and Natural Resources, UC Davis, UC Riverside and the University of Arizona, Tucson.

“While the results are a cause for concern, the situation in California is much better than in Florida and Texas, where ACP carrying the bacterium make up the majority of the population, and HLB is widespread in commercial citrus,” said researcher Neil McRoberts. McRoberts is a UC Davis plant pathologist and UC Integrated Pest Management Program affiliate advisor. “The results indicate that there is no room for complacency, but also no cause for panic.”

Since the first HLB-infected tree in California was found in 2012, nearly 4,000 infected trees have been detected and removed from residential properties in Southern California, mainly in Orange and Los Angeles counties. According to McRoberts, “to date, no HLB has been found in commercial citrus” in California. Roberts stressed, however, that the ACP study does not involve any testing of trees for HLB and focuses only on looking at the insect which spreads the bacterium.

McRoberts also emphasized that the project’s detections of the bacterium cannot be considered “official” because the researchers’ lab procedures differ from the official testing protocols of the California Department of Food and Agriculture (CDFA).

“Follow-up sampling by CDFA staff would allow official samples to be collected for further investigation, but is entirely voluntary for the growers involved,” McRoberts said. He added that his research team is currently wrapping up the sampling phase of the project, with data analysis continuing into 2023.

“Our study results indicate that it is not time to declare the emergency status for ACP/HLB in California over — the situation is still evolving,” McRoberts said.

Further information about the research can be obtained from McRoberts at or 530-752-3248.

Source: UC Agriculture and Natural Resources