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Wasp Drafted to Suck Life from Citrus Threat

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Tamarixia radiata is being enlisted throughout southern California because it literally sucks the life out of the Asian citrus psyllid, which spreads a disease fatal to all types of citrus trees.

Scientists have scoured spots around the globe for varieties of the wasp to battle the psyllid. For Southern California, the best bet appears to be a strain found in Pakistan’s Punjab region. The area has a desert climate similar to ours and also produces citrus.

The wasps are one millimeter long – not even as long as a dime is thick. University of California Riverside researcher Dr. Mark Hoddle personally transported the insects from Pakistan. His first stop was quarantine, where the wasps were tested against other pests and reviewed for any other possible effects, said Dr. Tracy Ellis, County of San Diego entomologist. Scientists decided any risk was low because it so specifically goes after the psyllid.

Teams began releasing Tamarixia around Southern California with the first batches let loose in San Diego in June.  Staff members from UC Riverside bring the wasps to locations identified by San Diego County’s Department of Agriculture, Weights and Measures as having high concentrations of the psyllid. So far, they’ve made 17 releases in the area, Ellis said. She said this method of “using nature to fight nature” has a good track record.

“It’s worked successfully on numerous citrus pests,” she said.

The Asian citrus psyllid was first discovered in San Diego County five years ago this month and has since become firmly established here. So far, we’ve been spared huanglongbing, or citrus greening, the bacterial disease the psyllid spreads.   

But Ellis warns, “Wherever the psyllid goes, the disease follows.”

It’s affected citrus growers around the world, Ellis said. Florida has seen its crops decimated. Local Agriculture, Weights and Measures inspectors have all been trained to watch for signs of the disease when out in the field.

The department’s recently-released crop report showed that in 2012 the San Diego region had 13,000 acres producing citrus with a value of $117 million. Ellis says huanglongbing could wipe that out.

“It’s a 100 percent threat,” she said.

Here are the somewhat gory, if barely visible, details.

Psyllids lay eggs on plants. Nymphs hatch from the eggs, and a nymph pokes a straw-like appendage into the plant to feed on its nutrients. In that process, it can pass along the huanglongbing bacteria. The nymphs stay fixed to one spot on the plant for days as they develop.

Enter Tamarixia.

The wasp will lay its own egg directly on the psyllid nymph. When the wasp hatches, it begins to consume its host. The wasp bores from the bottom right through the top of the psyllid, leaving a husk of the host with a hole where the wasp escapes.

The wasps lay one egg per psyllid, and each wasp can lay up to 300 eggs. So they can quickly take quite a toll on the psyllid population.  

“This wasp, if it became established, could really slow the spread of Asian citrus psyllid and bring it down to the level where it could be more manageable and not spread like wildfire like it is now,” Ellis said.

Currently there is only one small breeding site for the wasps at UC Riverside. Ellis said the plan is to create three sites, substantially increasing the number of wasps that can be released.

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Ellis explained a key benefit to using the wasp is that if you have citrus trees in your yard, you don’t have to do anything.

“People won’t even know they had a pest in the first place,” she said.

Ellis does say there are a couple things citrus owners can do to help. One is taking steps to control ants. Ants like problems on your citrus trees, so they defend trouble making insects like the psyllid. Argentine ants, the most common variety locally, will physically fight off Tamarixia trying to lay eggs on the psyllids. If you can limit ants, you’ll make it easier for the wasps to get a toehold.

You can also notify the Agriculture, Weights and Measures department if you find large concentrations of the psyllid or suspect your plants have been afflicted with huanglongbing. View office addresses and phone numbers

The release of this tiny wasp comes by the way of many dedicated people at University of California Riverside, the California Department of Food and Agriculture, the United States Department of Agriculture, the Citrus Research Board and the citrus industry.