California Citrus Research and Field Trials (CA-CRaFT) plans in Ventura County call for expanded activities and a stronger emphasis on biological control of the HLB-spreading Asian citrus psyllid (ACP) with the parasitic wasp Tamarixia radiata.
In a June 23 virtual presentation, Citrus Research Board integrated pest management entomologist Ivan Milosavljevic reported that the Ventura County program will utilize self-release T. radiata cage systems. The systems are designed to support parasitoid establishment and long-term ACP suppression under coastal citrus conditions. The effort will be focused exclusively on Ventura County coastal citrus systems and not on desert production regions.
PREVIOUS SUCCESSES
T. radiata has previously been used effectively for ACP biocontrol in California backyard citrus, starting in 2011. Milosavljevic reported that in the backyard citrus, ACP populations declined more than 75% in four years of T. radiata use.
Earlier this year, a Citrus Industry article reported that T. radiata is well established in Florida. Researchers have observed 30% or more parasitism of ACP nymphs by the parasitoid.
ARGENTINE ANT CONTROL ESSENTIAL
Milosavljevic emphasized the need to control Argentine ants, which limit T. radiata establishment and overall biological control success in California citrus. He reported that the ants aggressively protect more than 55% of ACP from natural enemies. In return, the ants are rewarded with food — honeydew — a sugary waste product excreted by ACP nymphs.
According to Milosavljevic, ant presence on trees triples ACP densities and reduces T. radiata parasitism by 50%. For that reason, growers need to control Argentine ants to maximize biocontrol of ACP.
The first California detection of ACP carrying the bacteria that spreads HLB in citrus was made in one tree in 2012. There were no such detections over the next two years. The number of detections of ACP carrying the bacteria peaked at 2,958 trees in 2023.
Milosavljevic’s presentation was part of the 2026 Citrus Research Board Webinar Series.
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