Tiny 'vampire' wasps take on invasive citrus psyllid
California's $2 billion dollar citrus industry is under attack by an invasive pest called the Asian citrus psyllid, which has spread to farms around the state and could end up wiping out entire groves of lemons, oranges and limes.
Luckily, scientists may have found a potential savior in the form of a Pakistani wasp that lives to attack the psyllid.
Its scientific name is Tamarixia radiata, said David Morgan with the California Department of Food and Agriculture, who is part of a $1.4 million state project started last year to breed and release the Tamarixia wasps into the wild.
"They are ridiculously small," he said, pointing out that each wasp is about the size of a grain of sea salt.
Scientists hope the wasps will hunt down Asian citrus psyllids by finding citrus trees, where the psylllid feeds on leaves.
The wasp will then puncture a hole in the aphid-sized bugs and suck out their juices, "just like a vampire," Morgan said.
Things get even more gruesome for the psyllids when the wasps reproduce, said Grace Radabaugh, also with the CDFA.
First, the female Tamarixia wasp stings a citrus psyllid, paralyzing it. Then it lays an egg under the helpless bug.
When the egg hatches, Radabaugh said, the wasp larva begins to feed on the slowly dying psyllid for several days.
When it's strong enough, the wasp then chews through the now mummified psyllid corpse and pops out the top of it.
"They emerge right out of that, like the science fiction movies," she says, alluding to the 1979 sci-fi classic "Alien," in which a larval alien gestates within the body of a human host. Sounding a bit like the cold-blooded android in "Alien," Radabaugh adds about the wasps: "They are a fascinating creature."
The reason California farmers are so eager to see the psyllid die such a horrifying death is that the bug often spreads a plant sickness called citrus greening disease, which turns fruit into green bitter lumps and kills every plant it infects. The disease has ravaged crops in Asia, Africa and other parts of the U.S.
Florida first detected the disease about a decade ago, and since then, 90,000 acres of crops have been wiped out.
The disease hasn’t taken hold in California. Yet.
UC Riverside entomologist Mark Hoddle said that, to keep it that way, the state needs to cut down the number of psyllids, something the Tamarixia wasp is perfectly suited to do.
"These bugs work 365 days of the year, 24 hours a day, seven days a week, and you don’t pay them anything," he said.
Hoddle was part of the team that first identified the Tamarixia wasps as a way of curbing the spread of Asian citrus psyllid.
The psyllid has spread around the world hiding on plants that have traveled across borders. With no natural enemies in their new location, the psyllid was free to spread.
That's why Hoddle went back to Pakistan to find out if the psyllid had an natural enemies there.
"It was like a needle in the haystack moment and a 'Eureka!' moment all at the same time," Hoddle said of finding the wasp.
After 18 months of testing, Hoddle and his team were able to prove that Tamarixia can't survive without the Asian citrus psyllid.
That means there’s no danger of the wasp attacking other bugs and spreading out of control. But because of this dependent relationship, the wasps tend to create an equilibrium with the psyllids, rather than wipe them out, says Philip Stansly with the University of Florida.
"They are not going to wipe out their only source of food. They are not stupid," he said of the wasps.
Stansly helped launch a similar wasp program in Florida, but he said the wasps only slowed the spread of citrus greening a little.
Ramping up efforts
"The biological control program is not a silver bullet solution for Asian citrus psyllid,” UC Riverside's Hoddle admitted. But he added that some help is better than none.
And, he said, the wasps are starting to spread on their own in the wild and may be able to curb psyllid populations by 50 percent in the future.
He is also seeking approval from the federal government to release a second type of wasp, Diaphorencyrtus aligarhensis, which also attacks the psyllids.
The federal government also sees Tamarixia wasps as a key player in this fight.
This week the U.S. Department of Agriculture said it will set side 1.5 million dollars to ramp up wasp breeding programs across the nation.
It the meantime, citrus farmers will have to continue using quarantines and pesticides to control the psyllids until a citrus greening resistant tree can be developed.