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Tomato psyllids are spreading across the country, devastating crops in Colorado, Montana, Washington, and Ontario, Canada. In Baja, Mexico, growers lost more than 85 percent of their fresh market tomatoes in 2001. California populations originated from Mexico, but are now surviving year-round in San Diego, Orange and Ventura counties.

Entomologists John Trumble, and Richard Stouthamer from the University of California, Riverside, studied the annual pattern of immigration of tomato psyllids into California tomato production areas using visual surveys and molecular techniques. Their results indicate how many psyllids it takes to cause crop damage and can help to estimate when and how much insecticide to use to control them.

The tomato psyllid can attack species in 20 plant families, but prefers to feed on tomato, potato, pepper, and eggplant. The name tomato psyllid is commonly used, but the pest is also known as potato psyllid when it feeds on potatoes.

“The psyllid is now a major problem on tomatoes and peppers in California, and potatoes and tomatoes in Texas,” says Trumble. “Currently, yellow sticky cards can be used as an early indicator of psyllid movement into an area, and plants on the field margins can be visually checked for eggs and nymphs.”

Female tomato psyllids can lay up to 1,000 eggs, and they inject a toxin that results in a condition called psyllid yellows that reduces photosynthesis and also reduces the level of nitrogen in tomatoes. It also causes the plant’s leaves to curl, and it produces smaller fruit. Researchers estimate that about 15 to 20 psyllids per plant during the course of a week cause stunting, from which most plants never recover.

Researchers found that for some tomato varieties, psyllids laid eggs on plants previously infested by nymphs far more than on uninfested control plants. This suggests that for some cultivars there is a physiological change in plant attractiveness following psyllid feeding.

Tomato psyllid density showed a strong correlation to the number of yellowing leaves and leaflets and distorted leaves. This discovery allows scientists to do simple visual surveys of yellowing leaves to estimate psyllid populations. Initial data suggests that about 18 nymphs per plant feeding for 7 to 10 days will cause psyllid yellows on tomatoes exposed during the first three weeks after transplanting.

The psyllid uses its piercing mouth parts to extract plant juices from foliage. Excess sugar, which the insect ingests, is excreted as small waxy beads of psyllid sugar (resembling granulated sugar). The adult psyllid is a small insect that has white or yellowish markings on the thorax, clear wings, and lines on the abdomen that separate segments.

The lack of information on reliable monitoring techniques makes early detection of these insects very difficult, leading growers in many areas to apply pesticide treatments.

“Relatively few reports are available on control using chemicals other than organophosphates or pyrethroids,” says Trumble. “We know that use of these materials in California causes a loss of biological control agents, resulting in outbreaks of secondary pests such as leafminers and spider mites. Imidacloprid is often injected through driplines in California, a practice that fits our IPM program because it doesn’t affect beneficial insects, yet provides additional control in the field.”

Trumble and his team are working to find new strategies for controlling the pest.

The UC Exotic/Invasive Pests and Diseases Research Program funded this three-year project. The program targets research on exotic pests and diseases in California. Its aim is not only to improve our knowledge and management of pests that are already here, but also to reduce the potential impact of those pests and diseases that pose a threat to the state. The program is collaboration between the UC Statewide Integrated Pest Management Program and the UC Riverside Center for Invasive Species Research. U.S. Department of Agriculture, Cooperative State Research Education and Extension Service, funds the program.

Media Contact:
John Trumble, Entomologist UC Riverside, (951) 827-5624