Bug vs bug: A foreign predatory wasp is released in Santa Maria to help fight citrus tree-loving pest

When you see the fruit on a citrus tree turn from orange or yellow to green, the tree isn’t growing limes. It’s most likely a sign that the tree has a disease called Huánglóngbing (HLB), otherwise known as citrus greening disease.

According to entomologist David Morgan, the disease is carried by the Asian citrus psyllid, a pest resembling an aphid that sucks on the phloem—the part of the plant that contains the sugars and nutrients created after photosynthesis. The disease is a bacteria injected into the plant as the psyllid feeds, but only if the pest is carrying HLB. The disease has decimated citrus crops in various parts of the world for decades.

click to enlarge Bug vs bug: A foreign predatory wasp is released in Santa Maria to help fight citrus tree-loving pest
PHOTO COURTESY OF THE CDFA
BUG-KILLING BUGS: The main diet of the 'Diaphorencyrtus aligarhensis' is the Asian citrus psyllid, which can also carry a disease known to decimate citrus fruit. The only instance of the disease in California was discovered in a Los Angeles County tree in 2012.

In California, HLB has only been detected in a single lemon tree from a residential area of Los Angeles County in 2012, according to the California Department of Food and Agriculture. The pest’s been detected in a total of 13 counties, all of Southern California—including Santa Barbara and San Luis Obispo counties—and as far north as Santa Clara County. And although the disease isn’t yet affecting the state’s citrus crops, the threat of it is enough to concern growers and state officials, who are now trying to eliminate the psyllid before any sort of widespread disease outbreak happens.

Morgan, who works for the state Department of Food and Agriculture specializing in biological control agents, got approval in December 2014 to release a tiny, predatory wasp in the Santa Maria area known as Diaphorencyrtus aligarhensis, which feeds on the citrus-eating psyllid. A different wasp, Tamarixia radiata, is also being used to try to keep the psyllid under wraps, but it doesn’t have a significant presence in Northern Santa Barbara County. Both wasp species are native to Pakistan, Morgan said.

“What we really wanted to do is carry out some releases where Tamarixia radiata was not present so that we can see whether it will establish better in the absence of the other agent or not,” Morgan said.

In 2011, the Tamarixia species was released in the state’s seven southernmost counties, not including Santa Barbara County, according to Morgan, who added that the wasp’s success is still being monitored in those areas.

Associates Insectary in Santa Paula, which makes its business in beneficial bugs, is currently breeding the Tamarixia wasps. Brad Chandler, the company’s president and general manager, said that breeding started with samples he’s collected in the wild because the bugs aren’t yet available for commercial use.

Chandler’s hoping to change that and is currently developing a large scale breeding system for Tamarixia. He said the state’s current method of breeding the wasps isn’t efficient.

Tamarixia is very expensive and labor intensive,” Chandler said. “We need hundreds of millions of them.”

Chandler uses the analogy of a Model T versus a Bentley.

“When you need a million of them, you go with the Model T,” Chandler said.

Chandler said that his company will breed them for the remainder of the year and should have full-scale production ready in about 18 months.

So now the state has two foreign wasp species on its hands. There are often unintended consequences when foreign species are introduced to a new area, so what about with these wasps?

According to food and agriculture department entomologist Morgan, there really aren’t any. He said the wasps underwent years of rigorous testing in quarantined research facilities before the department approved their release. The Diaphorencyrtus wasp has been used as a controlling mechanism for years in other parts of the country, such as Florida, where it’s shown some success, Morgan said.

The Diaphorencyrtus only eats psyllids such as the Asian citrus psyllid and the potato psyllid, which is also a non-native pest in California, Morgan said. Once the wasp’s food source disappears, then they just die off.

“It will die and nothing will have happened,” Morgan said. “There really is no impact that can be envisioned with these sorts of insects.”

And also, the wasps pose no danger to the public, he said. The wasp’s too small, about the size of a period on a piece of paper, and its stinger can’t penetrate human skin. 

“They’re the sort of insect that you can inhale without even noticing you swallowed an insect,” Morgan said. “They’re so small.”

Unfortunately, wasps alone won’t put a dent in the psyllid influx. Fighting the citrus pest will likely take multiple solutions, according to Alex Teague, senior vice president and chief operating officer for Limoneira, which owns 4,500 acres of citrus in Ventura County.

More than 100 years ago, Limoneira was the first in the state to use integrated pest management, according to Teague. And it’s not as simple as just spraying pesticides because they also kill the psyllid-eating wasps, Teague said.

“The psyllid [population] can grow probably faster than what the wasps can consume,” Teague said. “It’s got to be a combo of things.”

Morgan said the public can do its part by controlling ant populations. When the psyllid feeds on the phloem, it mainly targets the nutrients and not so much the sugar, which it excretes out its back end. It’s called honeydew, and ants can’t get enough.

“The ants prevent predators from getting to the psyllids,” Morgan said. “If you control the ants, you do a really good job at helping nature control the Asian citrus psyllid.”

 

Contact Staff Writer David Minsky at [email protected].

Comments (0)
Add a Comment