Battle of the Bugs: Good News for California Citrus Growers

UC Riverside’s Mark Hoddle released a natural enemy of Asian citrus psyllid in citrus grove on campus, Dec. 16

Jodie Holt, now the director of the UCR Botanic Gardens, poses with Chancellor Kim A. Wilcox. 
photo by Michael Lewis

Jodie Holt, now the director of the UCR Botanic Gardens, poses with Chancellor Kim A. Wilcox. photo by Michael Lewis

RIVERSIDE, Calif.  – Toward the end of 2011, Mark Hoddle, an entomologist at the University of California, Riverside, first released into a citrus grove on campus a batch of Pakistani wasps that are natural enemies of the Asian citrus psyllid (ACP), the vector of a bacterium that causes Huanglongbing (HLB), a lethal citrus disease.

On Tuesday, Dec. 16, Hoddle, the director of UCR’s Center for Invasive Species Research, released the wasp Diaphorencyrtus aligarhensis, a second species of ACP natural enemy, also from the Punjab region of Pakistan.  Chancellor Kim A. Wilcox and others involved in rearing insects on and off campus helped release the tiny wasps from vials.

The new wasp is about 1/16th of an inch long, half the size of a chocolate sprinkle.

Diaphorinocyrtus aligarhensis prepares to sting the young Asian citrus psyllid nymph. Photo credit: Mike Lewis, CISR, UC Riverside.

Diaphorinocyrtus aligarhensis prepares to sting the young Asian citrus psyllid nymph. Photo credit: Mike Lewis, CISR, UC Riverside.

Diaphorencyrtus aligarhensis, is a different species of natural enemy to Tamarixia radiata, the first ACP natural enemy from Pakistan that has been released and established in California for ACP biocontrol,” Hoddle said. “The second ACP-attacking species may provide additional pressure to ACP populations because it attacks different life stages and it may have different climate preferences.”

The new wasp attacks the second and third developmental stages of immature ACP (called nymphs) whereas Tamarixia attacks the larger nymphs in the fourth and fifth stages of development. ACP nymphs have five developmental stages, or instars, after they hatch from the egg.

Successful biocontrol of citrus pests in California sometimes requires more than one species of natural enemy because citrus is grown in a variety of different habitats – hot desert areas like Coachella, cooler coastal zones like Ventura, and intermediate areas like Riverside/Redlands and northern San Diego County.

Tamarixia and Diaphorencyrtus may have preferences for different micro-climates in different citrus growing regions and we want to make sure that we do all we can to minimize refuges for ACP infesting citrus in California,” Hoddle said.

Diaphorinocyrtus aligarhensis hunts around for suitable hosts for its eggs. The white trails are waste products secreted by the Asian citrus psyllid nymphs. Photo credit: Mike Lewis, CISR, UC Riverside.

Diaphorinocyrtus aligarhensis hunts around for suitable hosts for its eggs. The white trails are waste products secreted by the Asian citrus psyllid nymphs. Photo credit: Mike Lewis, CISR, UC Riverside.

Around  500 male and female wasps were released on Dec. 16. Only the female wasps kill the ACP. Females either lay their eggs inside the ACP nymph and the wasp larva feeds on the nymph (this is parasitism), or the female uses her ovipositor to stab the nymph until it bleeds. The female then eats this insect blood, which provides the protein she needs to mature eggs (this is host feeding).

“These natural enemies pose no risk to the environment,” Hoddle said. “They do not sting people or pets, and they don’t eat plants or spread disease. We are hoping that initially we will be able to establish these new natural enemies, monitor their spread and then evaluate their impact. Predicting their performance ahead of time is not possible.”

Hoddle’s lab has developed a release plan for Diaphorencyrtus. Initial releases will focus on parts of Southern California with ACP infestations in urban areas but where Tamarixia has not been released.

The first release of a new wasp drew a crowd, mostly people who are personally involved in raising wasps.

The first release of a new wasp drew a crowd, mostly people who are personally involved in raising wasps. photo by Michael Lewis

“This is because we want to minimize competition between these two wasp species in the initial establishment phase,” Hoddle explained. “Further, we will work closely with the California Department of Food and Agriculture on identifying places to concentrate our release efforts.”

Hoddle’s plan is to gradually transition production of the new wasp over to the California Department of Food and Agriculture (CDFA) then onto private insectaries interested in rearing this natural enemy. For the first 12-18 months, UCR and then later the CDFA will be leading the rearing and release program for this new ACP natural enemy.

Hoddle and his team will be available for media interviews on the wasp and its potential as a biocontrol agent, the ACP problem and its impact, what UCR is doing about the ACP threat, how it is partnering with the Citrus Research Board, the CDFA and the U.S. Department of Agriculture, and what progress has been made so far in controlling the ACP spread in the state.  CFDA representatives will also be present.

About ACP-HLB:

ACP-HLB is a serious threat to California’s annual $2 billion citrus industry. This insect-disease combination has cost Florida’s citrus industry $1.3 billion in losses, production costs have increased by 40 percent, and more than 6,000 jobs have been lost as citrus trees have died and the industry has contracted.

When ACP feeds on citrus leaves and stems, it damages the tree by injecting a toxin that causes leaves to twist and die. The more serious issue is that ACP spreads a bacterium that causes HLB. Trees with HLB have mottled leaves and small bitter fruit.  Trees die within about 8 years of infection. To date there is no known cure for HLB.

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