Biological Control Leads to ‘Massive Decline’ in Psyllids

Repeated evaluations throughout California showed “a massive decline – greater than 70%” in HLB-spreading Asian citrus psyllid (ACP) densities since the inception of a biological control program, a researcher reported recently.

Mark Hoddle said the University of California, Riverside (UCR) and the California Department of Food and Agriculture (CDFA) turned to biocontrol because insecticide spraying wasn’t adequately controlling the psyllid. Hoddle is a biological control specialist at the UCR Department of Entomology.

Hoddle reported that ACP was first detected in California in San Diego County in 2008. HLB was first found in Los Angeles County in 2012. Learn more about HLB in California here. 

In the search for the proper biocontrol, researchers in 2010 went to an area of Pakistan that was somewhat similar weatherwise to Bakersfield, California, Hoddle said. In Pakistan, he was surprised to find orchards looking healthy “and they were producing tons and tons of fruit, literally.”

Researchers in Pakistan found the ACP parasitoid Tamarixia radiata and learned that it established readily in California. T. radiata were first released in California in December 2011. Hoddle reported that CDFA had released 23 million T. radiata in California by 2022.

Along with reporting on the huge decline in California ACP populations as a result of biocontrol, Hoddle said that:

• Eleven years after the initial HLB detection in California, it is highly unlikely California citrus will be destroyed by ACP/HLB.
• The ACP biocontrol program, in part, has contributed to this outcome as vector densities are now very low. The densities are so low that CDFA is considering discontinuing ACP population density monitoring because many of its study sites have been ACP-free for more than two years.
• Natural enemies have achieved far greater levels of ACP suppression over much vaster areas far more cheaply and sustainably than was ever possible with urban spray programs.
• Because of such low ACP densities, of the millions of citrus trees grown in urban areas in California, only 6,000 trees have succumbed to HLB, which Hoddle called “a miniscule fraction.”

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