Scientists releasing more wasps to save California's citrus trees

Diaphorencyrtus aligarhensis, a natural enemy of the Asian citrus psyllid, is seen here on the edge of a penny.
Diaphorencyrtus aligarhensis, a natural enemy of the Asian citrus psyllid, is seen here on the edge of a penny. MIKE LEWIS, CISR, UC RIVERSIDE

A new species of imported wasp will be released in California on Tuesday to help curb the spread of the invasive Asian citrus psyllid.

The aphid sized psyllid can carry a disease known as citrus greening that turns fruit into bitter green lumps and can slowly kill off entire groves of lemons, limes and oranges.

(The invasive Asian citrus psyllid (Diaphorina citri). The bug is about an eighth of an inch long. Photo: Mike Lewis / UC Riverside)

Luckily for citrus growers, this tiny wasp known scientifically as Diaphorencyrtus aligarhensis, acts as a parasiteattacking the psyllid when it's a young nymph, said UC Riverside entomologist Mark Hoddle.

"The female parasite lays her egg directly into the central body cavity of the Asian citrus pysllid nymph," he said. "The larva of [the wasp] basically eats its way from the inside out."

It's a gruesome way to go.

(Diaphorinocyrtus aligarhensis prepares to sting the young Asian citrus psyllid nymph. Photo: Mike Lewis / UC Riverside)

But don't feel too bad for the psyllid. This pest spread citrus greening disease in Florida and over the last decade more than 90,000 acres of crops have been lost.

If the disease takes hold on the west coast, California's 2 billion dollar citrus industry would be at risk.

So far only one tree in California has been found to carry the disease and researchers believe that plant caught the sickness from an illegally imported graft, not from a psyllid.

This is the second species of wasp approved by the FDA to be used as a biological control for the psyllids.

The first was a variety known as Tamarixia radiata. So far about 850 thousand of those have been released.

Hoddle said there are no signs those wasps are messing with the larger California ecosystem.

"So far we've found no species of insect being attacked by the parasite other than Asian citrus psyllid, so that's really good news for us," he told KPCC.

Both species of wasps attack the psyllid during its early development, but they attack at different phases.

Hoddle believes this combined approach could help cut the psyllid's numbers in California by 30% or more.

On Tuesday, Hoddle and his colleagues will release about 300 Diaphorinocyrtus wasps in a test grove on the UC Riverside campus.

Starting in January of next year they plan to release more in areas around the Coachella Valley and L.A. County.

"If we can release 10,000 or more next year, that would be a really good start for the program," Hoddle said.

The wasps are about the size of a grain of sea salt and are too small to harm humans.

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