An Asian Citrus Psyllid feeds on a lemon tree leaf. (Credit: Mike Lewis)

Mark Hoddle has the makings of a Hollywood blockbuster. That’s not something one usually says about an entomologist. The script might start this way:


UC Cooperative Extension biological control specialist Mark and his wife Christina, assistant specialist in entomology, deplane in Lahore, Pakistan, on the hunt for a natural-born predator that attacks the Asian citrus psyllid. They need to find neutralize the citrus psyllid because it’s an invasive insect that has California’s citrus industry shakento its root stocks.

The Hoddles had their sights set on Tamarixia radiata, a wasp smaller than a chocolate sprinkle, Mark Hoddle says.

As Hoddle explained to the California Report, the female likes to  lay eggs in, not to mention eat, the nymphs of the Asian citrus psyllid. “She uses something called an ovipositor, which is kind of like a syringe. She stabs a nymph with that syringe and then injects an egg. When that egg hatches, the larvae feeds on the psyllid, killing it.”

The wasp also uses its ovipositor to eat the psyllid, stabbing it then lapping up the guts that ooze from the puncture wounds. “Like a kitten,” Hoddle says.

Where the Asian Citrus Psyllid has been found in far. (Credit:USDA)

Believed to have originated somewhere on the Indian subcontinent, the Asian citrus psyllid has made its way to the Middle East and the Americas. It was first found in the US in Florida in 1998. As far as we know, it reached California in 2008, along the Mexican border.

Since then, the Asian citrus psyllid has flown or hitchhiked its way inexorably northward into the backyards of Los Angeles, San Bernardino and Riverside counties. They eat the leaves and stems of citrus trees, injecting a toxin as they go.

The leaves twist and die.  Worse, some of the psyllids are carrying a  bacterium that causes Huanglongbing, or citrus greening. The leaves on infected trees turn yellowand the fruit becomes hard and bitter before the tree expires. Huanglongbing has not been found in California – yet – but commercial citrus growers are really, really worried about it. As is the USDA.

Tamarixia radiata from humid parts of China and Vietnam have been feasting on Asian citrus psyllids in Florida with zest. So the Hoddles thought they should head to the Punjab because “that particular part of the world has a very good climate match with California.”

But of course, the question rises … what about unintended consequences?

There are many instances of problems addressed with invasive species that became problems in their own right. Who can forget the story of the cane toad in Australia?

Hoddle says Tamarixia radiata “is highly evolved to feed just on Asian citrus psyllid. So for this parasite to sort of de-evolve and become more of a generalist parasite would require an immense number of biological, physical, biochemical and behavioral changes.”

On the left, a Tamarixia radiata wasp. On the right, the dried husk of an Asian citrus psyllid from which an adult wasp has burst after 12 days of incubation. (Credit: Mike Lewis)

After an early test release behind the home of UC Riverside Chancellor Tim White (already known to fans of Undercover Boss as a guy game to experiment), state and federal regulators appear to be comfortable with the idea that UC scientists will raise thousands of Tamarixia radiata for release throughout California, starting in Los Angeles.

Hoddle says Tamarixia radiata won’t eradicate Asian citrus psyllid. Commercial citrus producers in California will still continue to apply insecticides to prevent the spread of Huanglongbing. But, he says, state regulators have already determined backyard pesticide applications are too expensive ($10-11 million so far) and too ineffective to bother with.

One final note: Hoddle collected the parasites in collaboration with scientists at the University of Agriculture in Faisalabad. As it happens, the university’s vice chancellor, Iqrar Khan, is a UC Riverside graduate. It’s a small world, after all.


Rachael Myrow

From KQED’s Silicon Valley Bureau in San Jose, Rachael Myrow covers arts and culture in San Mateo, Santa Clara and Santa Cruz Counties. This follows more than seven years hosting KQED's California Report, broadcast on NPR affiliates throughout the state. She still guest hosts for The California Report and Forum, and files for NPR and PRI’s The World. Before KQED, she worked in Los Angeles for Marketplace and KPCC.

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