To a large extent, California’s citrus industry has Mark Hoddle to thank for the latest effort to combat the Asian citrus psyllid.
The psyllid, which can transmit huanglongbing, or HLB, a disease that wipes out citrus trees, first was discovered in the state in 2008, and since has shown up in several counties.
The presence of the psyllid became much more problematic in March, when HLB, also known as citrus greening disease, was found on a tree in a Southern California back yard.
Eventually, growers and scientists alike expect the psyllid and the disease to start showing up in the major citrus-growing areas in the northern part of the state.
But Hoddle and his researchers, in cooperation with California’s Department of Food and Agriculture and growers themselves, are doing everything they can to slow the advance of the psyllid.
A natural enemy
An extension specialist in biological control and director of the Center for Invasive Species Research in the entomology department of the University of California-Riverside, Hoddle found that the psyllid was thriving in Southern California because it had no natural enemies there.
After conducting some research, he determined that the Punjab region of Pakistan, where the psyllids are native, has a climate that matches California’s and is home to natural enemies of the psyllid — a wasp known as Tamarixia radiata.
Hoddle and his wife, Christina, an entomologist who works with him in his laboratory, made five trips to Pakistan over two years to collect parasites, which were allowed to reproduce in the laboratory.
In December, Hoddle released the first of 18,000 wasps that had been spread as of early October at 70 different sites.
Every Friday, Hoddle and a couple of his lab technicians, armed with a list of potential psyllid sites, meet up with CDFA representatives, find psyllid-infested trees and release more parasites.
They go back later and check to see if the parasites established themselves and, if so, find out how far out they’ve spread.
Hoddle said he’s been getting “reasonably good” recovery rates. The wasps establish themselves about 50% of the time.
The wasps were not introduced into the area where the disease was discovered. That area was sprayed with pesticide, which does a better job of eliminating the psyllids.
“It’s best to go in with a scorched earth-type policy and just kill everything,” he said.
Wasps would not kill every last psyllid, like the spray will, he said.
“There’s always the risk that a few will escape.”
Although a few psyllids have shown up in the commercial growing regions in northern regions, they have been knocked out with pesticides as soon as they were discovered and have not become established there.
Until that happens, efforts will continue to contain the psyllid in southern regions — a challenge because of plant smuggling and the suspicion that backyard psyllid-infested plants are given as gifts or spread to other areas as residents move.
“They represent a high dispersal threat into commercial production areas,” Hoddle said.
Hoddle is pleased with the proactive efforts being made in California to control both the psyllids and the disease.
“They’re keeping a close eye on the spread, and when they make detections, they swoop into action and deal with it quickly,” he said