Cal Poly Pomona plant science faculty and students have supported efforts to breed an army of wasps in a silent, but desperate war to save California's citrus industry from a deadly disease.

The incurable disease known as Huanglongbing (HLB) is responsible for decimating the Florida citrus industry, and it has found its way to California. Growers have found the disease in more than 900 citrus trees across Los Angeles, Orange and Riverside counties - including more than 600 cases this year alone.

The disease is spread by an insect known as the Asian citrus psyllid. Agricultural officials are employing a strategy of biological control to stop the psyllid, using a tiny wasp known as Tamarixia radiata to prey upon the psyllid. Cal Poly Pomona faculty and students are helping to breed the wasps, which the California Department of Food of Agriculture (CDFA) release in Southern California.

"It is an effort that has given our students tremendous hands-on educational and research opportunities involving both the psyllid and Tamarixia," said Anna Soper, an assistant professor in the plant science department.

Cal Poly Pomona developed a partnership with the CDFA, the Citrus Research Board, UC Riverside and the Citrus Pest & Disease Prevention Program that led to the construction of a grant-funded greenhouse completed on campus in 2016.

Since then, the CDFA has reared more than 1.4 million Tamarixia for the war against the psyllid in the safe, contained environment of the greenhouse. In addition, the greenhouse has allowed faculty and students to conduct research into such subjects as how different diets might affect the wasps' fertility and longevity and whether sound and olfactory components might lure the psyllids.

Although suburban Southern California is no longer a major commercial citrus growing region, between 50 and 70 percent of homes in the area have citrus trees, creating a large breeding ground for the psyllids - and the problem threatens to spread beyond to California's $3 billion citrus industry.

"California citrus is facing its biggest threat yet in HLB, and the department has been working diligently with our partners to identify multiple tools that can play a part in fighting this disease," said Victoria Hornbaker, interim director of the citrus program at the California Department of Food and Agriculture.

Huanglongbing has devastated the Florida commercial citrus industry. Over the course of a decade, the industry lost $7.8 billion in revenue, 162,200 acres of citrus, and more than 7,500 jobs to the disease.

For Max Lasiter, a graduate student involved in the psyllid and Tamarixia research, the disease hits close to home. His family owns citrus groves in central California.

"I'm focusing on hopefully finding a way to increase plant health to the point that the tree might be able to sustain itself a little bit better and be economically viable even if it does contract the disease," he said.

The wasp is a natural predator of the psyllid: it kills the psyllid either by eating it or laying its eggs on it. It doesn't prey upon other insects, making it an environmentally friendly and economical means of suppressing the psyllid populations.

In addition to the Tamarixia bred at Cal Poly Pomona, the CDFA has produced nearly 6.1 million of the wasps since 2014. As a result, CDFA researchers have found that the number of psyllids in urban areas have declined by at least 80 percent since 2015.

Although Tamarixia will help control the psyllids and the spread of Huanglongbing, it will not stop the disease on its own. Agricultural officials need homeowners to help out and have provided a number of tips:

• For Tamarixia to be effective, ant control is critical. Ants protect the Asian citrus psyllid from predators, like Tamarixia. Homeowners can do their part by placing ant bait - not spray - around citrus trees and controlling ants throughout their yard.
• Inspect trees monthly for symptoms of Huanglongbing, and whenever watering, spraying, pruning or tending trees. If you spot the pest or disease, call: 800-491-1899. Symptoms include:
  • Blotchy and un-even yellowing leaves
  • Premature and excessive fruit drop
  • Lopsided fruit
  • Bitter, uneatable fruit
• Do not move citrus plants, foliage or fruit into or out of your area, and especially across state or international borders. This could unknowingly contribute to the spread of the pest and disease.
• As part of your tree care, visit your local nursery or garden center to get advice on products that can help protect your citrus tree.
• When planting a new citrus tree, be sure to get your tree from a reputable, licensed nursery in your local area.
• When grafting citrus trees, only use registered budwood that comes with source documentation, such as the budwood offered through the Citrus Clonal Protection Program.

• Be sure to dry out citrus tree clippings or double bag them before removing the plant material from the property.