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Battling A Small Pest To Keep California Citrus Flourishing

UC Riverside researcher Mark Hoddle
Nicholas McVicker
UC Riverside researcher Mark Hoddle
Battling A Small Pest To Keep California Citrus Flourishing
Battling A Small Pest To Keep California Citrus Flourishing
California's citrus industry is being threatened by the same pest that has caused billions of dollars of damage in Florida. Local growers are hoping an imported wasp will help in the effort to keep citrus greening disease from gaining a foothold here.

Congress set aside $125 million in the new farm bill to help beat back an attack on the nation's citrus trees.

Greening disease already has cost the Florida citrus industry billions and Southern California researchers want to keep the illness out of this state's commercial groves.

A tiny Pakastani import is helping growers here wage war on a bug that spreads the disease.


The Pauma Valley cuts across the northern part of San Diego County. Four generations of Lyalls have farmed here, but Andy Lyall worries that's about to change because a tiny leaf-sucking bug know as the Asian citrus psyllid is laying siege to his livelihood.

"They'll land on that leaf and they have a sharp mouth part that they literally poke into the leaf," Lyall said. "And (then they) suck the fluid out. And in the process then, they can infect that tree just like with a hypodermic needle."

The infection is untreatable and fatal. Huanglongbing disease, more commonly called citrus greening illness, already is ravaging Florida's groves. It is costing farmers there billions.

The Asian citrus psyllid that spreads the disease, according to San Diego County entomologist Tracy Ellis, is already here in force.

"Whenever the insect arrives, the disease quickly follows," Ellis said. "It was a 5-year gap between Florida's detection of the psyllid and the detection of the disease."


The illness has officially only been found in one tree in Los Angeles County, said Mark Hoddle, an entomologist at the University of California-Riverside. He suspects the local situation is more dire.

"Given the vast number of citrus trees growing in southern California it is highly likely that there are many other trees in residential areas that have the disease, but we just have not found them yet," Hoddle said.

"But it is likely that the psyllid has found those trees, it has acquired the bacteria and it is now spreading it to more and more healthy trees," Hoddle said.

That's why Hoddle is focusing on the insect that spreads the illness. A small wasp from Pakistan is proving to be a capable foot soldier.

A wasp, Tamarixia radiata, injects an Asian citrus psyllid with eggs.  Those eggs will hatch and kill the psyllid.
Mark Huddle, UC Riverside
A wasp, Tamarixia radiata, injects an Asian citrus psyllid with eggs. Those eggs will hatch and kill the psyllid.

"They attack the nymphs, or the immature stages of the psyllid," Hoddle said. "The females lay their eggs inside these nymphs. Those parasite eggs hatch. And a tiny larvae, like a little fly maggot, just slowly eats the inside of the nymph. Eventually killing it."

Extensive testing during an 18-month quarantine suggests the psyllid is the only food the wasp is interested in. Without psyllids, the wasps die out.

Hoddle said they are very effective at seeking out and finding their prey. But a big challenge is raising enough wasps to have an impact. Part of that work happens at UC Riverside, but Hoddle said it's tedious.

"We have to grow a citrus plant. And on that plant we have to grow a citrus psyllid. Then on those we have to put the parasites which attack the Asian citrus psyllid, Huddle said.

About 10 days later, those parasites will hatch out of those parasitized nymphs.

Even in a small breeding room, researchers can still raise 6,000 to 10,000 wasps a week.

Once the wasps are mature, workers use a vacuum tube to suck the insects into small plastic vials. The vials are taken out into the field and hung up in trees where the psyllids have been detected.

"And when that vial is hanging in the tree parasites come out," Hoddle said.

But Southern California is a huge region. Hoddle said just raising enough wasps to be effective on a large scale is a major challenge.

And once the wasps are in the field they also have to contend with Argentine ants.

"The Asian citrus psyllid nymps are producing this sugary substance called honeydew. And when that honeydew is produced, the ants find it," said Grace Raddabaugh, a field technician working for the California Department of Food and Agriculture.

"And they feed on it and they take it back to their nests. And it's a food source for them," Raddabaugh said.

And the ants will fight the Pakastani wasps to keep that sweet food on the menu. Researchers say the best thing that backyard gardeners can do to help control the psyllid, is to focus on controlling Argentine ants.

Meanwhile, San Diego County farmers like Andy Lyall regularly inspect their groves. He shakes trees in their groves to check for psyllids. Lyall does what he can with pesticides. And he remains hopeful that researchers will find a way to stop the illness before it infects a commercial grove.

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