US: Beneficial wasp introduced to Imperial Valley to combat HLB

Date:12-28-2020

By Katherine Ramos

The California Department of Food and Agriculture began releasing thousands of parasitic wasps, Tamarixia radiata, on December 10, into the urban neighborhoods of Imperial County to combat the spread of the Asian citrus psyllid — the pest that carries Huanglongbing (HLB) disease.

HLB is an incurable disease that kills citrus trees and has been found in more than 2,000 residential trees in Los Angeles, Orange, Riverside, and San Bernardino counties. Symptoms of HLB are yellowing leaves, yellowing shoots, small and bitter fruits, and premature and excessive fruit drop. Eventually, the infected tree will die and must be removed to prevent the spread.

The Asian citrus psyllid or ACP feeds on the leaves and carries the disease when they travel from plant to plant. Within a short time, the pest infects multiple trees. It can take up to two years for the signs of HLB to begin to show, and by that time, it’s too late for the plant.

The Tamarixia is the natural predator of the ACP and was brought in to combat the pest. Dr. David Morgan with CDFA’s Citrus Pest and Disease Control unit said the University of California Riverside has thoroughly tested and retested to make sure the wasp was okay to use as a biological pest control

The first releases of Tamarixia in urban areas were in Riverside in December of 2011, and shortly after were released in Azusa and LA. So far it has been released in Palm Springs, Brawley, and other Southern California locations totaling 4,000 square miles.

“We only concentrate on urban areas because that is where we can give the greatest benefit by releasing these beneficial insects,” said Morgan.

Morgan said the insect was released in as many urban areas and trade routes as possible until 2017. Now, the CDFA only releases the insect in high-risk areas such as LA and Riverside. They have also been released near the borders of Arizona and Mexico.

The pest and the disease were first found in Florida citrus groves before 2000, causing thousands of the dollars in damage to the citrus industry in the State.

With the knowledge from the Florida incident, Morgan said it was only a matter of when, not if, the disease would appear in the California.

Morgan said while the wasps will slow down the spread of the psyllids, it will not stop HLB. That will have to take quarantining, treatment, and tree removal. There is hope, according to Morgan, since CDFA is currently researching citrus plants that are resistant to the disease with the hopes of developing one that will not die from HLB.

Morgan said these wasps, despite the public fear associated with the insect species, do not harm people nor other plants or insects. The tiny, period-sized wasp feeds solely on the ACP. Residents are also asked to control ants on the citrus trees that could possibly kill the beneficial wasp.

Due to the release of Tamarixia, Morgan said there has been a 95 percent decrease in the population of the ACP. With release of the beneficial wasps, there is hope to keep the California citrus industry booming.

“We are lucky to live in California, this State is just fantastic when it comes to agriculture. We produce more than 80 percent of the fresh citrus fruit for our Nation and its considered high quality,” said Morgan.

This has not been the first time a biological pest control has been released in the Imperial Valley. In 2000 the CDFA had an insectary based in Brawley to counteract the pink hibiscus mealybug, which rid the area of the pest.

For residents who suspect their citrus trees might have HLB, the CDFA pest hotline is 1-800-491-1899.