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State Lab Cultivates Wasp To Combat Citrus Pest

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EDINBURG, Texas (CBSDFW.COM/AP) — Sometimes, it takes a bug to kill a bug.

And a wasp no bigger than a pinprick may be the Texas citrus industry’s best weapon against the Asian citrus psyllid, a jumping lice that can infect trees with a devastating disease known as citrus greening.

The wasp — its formal name is Tamarixia radiata — likewise originates in Asia. And much as the psyllid feeds off the sap of citrus trees, the wasp feeds off the insides of the psyllid.

The adult female lays an egg beneath the psyllid, which hatches into a larva that literally sucks the life out of the psyllid from beneath. The larva eventually takes residence, continuing to grow inside the lifeless husk before reaching adulthood and chewing its way out.

“We call them mummies,” Daniel Flores, an Edinburg-based U.S. Department of Agriculture entomologist, said of the deceased psyllids.

While the psyllid itself is harmless, the bacteria it may carry are the kiss of death to citrus trees. The bacteria cause a vascular disease known as Huanglongbing, or citrus greening.

“All of a sudden you’ll notice that on this big, bushy tree, there’s this one branch, and all of the leaves off of that branch are yellow,” Flores told the San Antonio Express-News.

Next, the fruit becomes bitter, mottled and misshapen.

(credit: CBSDFW.COM)

(credit: CBSDFW.COM)

The disease eventually spreads through the tree’s veins to the canopy and root system, killing it.

While citrus greening has already devastated citrus groves throughout Florida, scientists in California and Texas hope the wasp can be deployed preemptively against the psyllid, and therefore Huanglongbing.

The disease so far has appeared in just one backyard in the California and, last year, two adjacent orchards in San Juan, a Rio Grande Valley community just north of the Mexican border.

Both discoveries prompted officials to set up quarantine zones stretching several miles around the infection.

Ray Prewett, president of the trade group Texas Citrus Mutual, said the grove owner recently made the costly and difficult decision to pull out some of his best producing trees, which were asymptomatic but still could have been infected. The grower’s losses were steep.

Mark Hoddle, a biological control expert at University of California, Riverside, collected and carried the wasps to California from Pakistan So far, he’s released about 80,000 in backyards throughout Southern California.

“The parasite appears to have established,” he said.

Flores, the USDA scientist, had some sent via Federal Express from Pakistan to a border inspection station about 90 minutes away from theUSDA quarantine facility near Harlingen in August 2009.

Their arrival — they were chilled and packed in Styrofoam boxes — took on the urgency of an ambulance ride.

“It was like, ‘We’re trying to save the world — get out of the way!'” he recalled.

After about two years of testing to make sure the wasp would attack only the Asian citrus psyllid, it was time to begin mass production.

By partnering with Hidalgo County horticulturist Barbara Storz and a network of trained “master gardeners,” researchers were able to find trees to grow wasp populations.

Commercial groves weren’t usable because use of pesticides would work against the wasp, Storz explained.

But there are yards across the Valley with lemon and lime trees, and many of the “Winter Texan” trailer parks scattered across Hidalgo County — home to people from out of state who seek South Texas’ warm climate in the winter — were built on former citrus groves and retained some orange and grapefruit trees. There are more than 60 such parks in the quarantine zone, Storz said.

Locals have volunteered trees that are hedged to allow for new growth that is irresistible to psyllids.

“We’re talking like a buffet for psyllids,” Flores said.

The trees are covered with meshed caging, and the wasps are brought in.

About 700 will be introduced to a given tree. When the tree is uncovered two to three months later, it will have produced about 11,000.

More are produced in smaller trees, known as “bug dorms,” in Flores’ Edinburg lab.

Of the approximately 100,000 produced there per month, about half are introduced to backyard trees throughout the Valley, where it’s hoped the wasps will begin to spread on their own. The other 50,000 are picked up by authorities from across the border in Tamaulipas, Mexico, where citrus trees also grow in a lot of neighborhoods.

The goal, Flores said, is to create a “biological barrier.”

Whether such a barrier would have prevented the disease’s appearance in Texas is unclear.

A disease-carrying psyllid could have wafted across the Rio Grande or rode in on a fruit shipment.

It also could have been transported unknowingly, perhaps by a winter Texan bringing a potted lemon or lime tree from a previous wintering ground in Florida.

Since the disease can be dormant for years before attacking the tree, the traveler wouldn’t have known.

“There’s no smoking citrus tree, so to speak,” said Larry Hawkins, a California-based USDA spokesman. “You can buy a tree that looks perfectly normal, move it from one state to another and plant it and actually be moving that disease.”