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Science update on whiteflies.

It sports a new scientific name but hasn't dodged its scientific pursuers. They are sharpening their focus on strategies with potential to control the insect called biotype B of the sweetpotato whitefly (Bemisia tabaci) and, by some, the silverleaf whitefly.

In March 1994, an article was published in Annals of the Entomological Society of America that establishes biotype B as a new species, Bemisia argentifolii.

This pest--whatever name you use--has afflicted American agriculture since 1986. It transmits plant diseases, feeds on crops, and contaminates them with sticky sugars. Annual income losses are estimated at over $200 million in cotton, melons, and many other crops mostly in Arizona, California, Florida, and Texas.

ARS led development of a coordinated 5-year research and action plan implemented in 1992. This past January, 185 USDA, university, state, and industry experts met in Orlando, Florida, to hold the plan's second annual progress review--and to share new knowledge about whitefly threats.

For example, scientists with the University of Arizona and an ARS lab in Montpellier, France, said the pest is apparently dispersing throughout Asia and within the Mediterranean Basin. They have found it for the first time in Spain, Cyprus, Egypt, and Pakistan.

ARS coordinated the January meeting with other USDA agencies, the University of California, and University of Florida. Some other highlights from the meeting:

Viruses and Other Maladies

Researchers continue identifying new whitefly-transmitted viruses, such as cucurbit yellow stunting disorder virus. It attacks melons and cucumbers but fortunately has been found only in the Middle East. An ARS scientist in Salinas, California, and an Israeli colleague identified it.

New findings about a disorder called squash silverleaf may eventually shed light on its whitefly-related cause and lead to controlling it, perhaps by boosting or regulating the squash plant's defenses. The disorder first appeared in Florida. ARS scientists in Orlando have ruled out viruses, bacteria, and fungi. Their recent measurements of proteins in squash plants fed on by whiteflies suggest the disorder may result from the plants' own response to the insects' chemical secretions.

A Sticky Problem Finally Coming Unglued?

Whiteflies deposit sugars on cotton lint in bolls, and the sticky fiber severely gums up ginning and textile machinery. But the textile industry may see some relief as early as next year. ARS scientists in Phoenix, Arizona, reduced the stickiness up to 82 percent by spraying--just before harvest--a mix of enzymes developed with a private firm.

To Spray or Not To Spray--What, When, Where, and How

Clustering on leaf undersides, whiteflies are partly shielded from insecticides--to which they readily become resistant.

New tests in cotton and other crops support rotating different insecticides and other controls to delay resistance. ARS scientists in Phoenix developed new sampling methods to gauge when whitefly numbers rise enough to merit spraying cotton. Larger studies will validate the methods, which could lead to less insecticide use and higher net returns.

Insecticide covered more of the lower surfaces of cotton leaves in tests of an electrostatic spray charging system designed for aircraft by an ARS scientist in College Station, Texas.

Helping Natural Enemies Turn the Tide

Many fungi and insect parasites and predators have potential as biological controls, but researchers say they will more likely succeed across large areas rather than in single fields. ARS scientists in Weslaco, Texas, are leading an interagency project to design, carry out, and evaluate whitefly biocontrol in the Lower Rio Grande Valley of Texas. At study sites--nine cottonfields within a square-mile area of other crops--the scientists collect extensive data linking populations of whiteflies and their natural enemies to weather, crops, and farming methods.

For biocontrol agents not native to the United States, researchers depend mostly on explorations by ARS scientists based in France. Their collections have concentrated on Europe, the Middle East, and Asia. This year, they will also search--for fungi--in the humid tropics of South America and Southeast Asia.

For further information about ARS whitefly research, contact Robert Faust or James Coppedge, USDA-ARS National Program Staff, Building 005, 10300 Baltimore Ave., Beltsville, MD 20705; phone (301) 504-6918 (Faust) or 504-5541 (Coppedge).
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Author:De Quattro, Jim
Publication:Agricultural Research
Date:Apr 1, 1994
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