Breakthrough in Whitefly Fight Reported : Science: The bug is a distinct species and not just another common strain, researchers report. If true, the search for a natural enemy could be made easier.

In a discovery that holds major implications for control of one of the worst agricultural pests to hit the Southwest in decades, scientists at UC Riverside say the so-called strain B whitefly is a distinct species and not just another strain of the common sweet potato whitefly.

The scientists, whose findings were published in today’s issue of the journal Science, are now calling the bug the silverleaf whitefly, for the silvery-looking damage it causes on squash plant leaves.

Although other researchers have expressed doubts about the report, Thomas M. Perring, an entomologist and leader of the university’s scientific team, said the identification of the insect as a separate species will have a “tremendous impact” on the search for natural enemies to control the pest. “That impact is to simply accelerate the success rate of locating a natural enemy” to the bug that has caused an estimated $500 million in crop damage in the last two years, he said.

While scientists and agricultural specialists have been scrambling to develop and institute a variety of crop-based programs to reduce the damage from the voracious pest, dozens of research projects have been aimed at finding a natural enemy to prey on the bug without damaging the crops. Most of those projects have been stymied by the new bug’s resistance to enemies that helped control the sweet potato fly.

Since it was first seen in 1986, the new whitefly had been thought to be a strain of the sweet potato whitefly and has been variously called the cotton, poinsettia, Florida or B strain. Perring said identification as a separate species will help researchers narrow the painstaking process of locating and testing enemies, especially parasites that can be very picky predators. Such biological controls are often the most effective, safest means of eradicating pests.

And farmers want the silverleaf whitefly eradicated. For two years it has been decimating crops such as melons, broccoli and cotton throughout the South and Southwest, particularly in Mexico, Texas, Arizona, and California’s Imperial Valley. This year, the bug was found in California’s Central Valley--one of the most productive agricultural areas in the world.

Perring said the team used four different tests, including genetic tests, to determine that the silverleaf whitefly was distinct from the sweet potato whitefly. However, in an adjoining article in Science, other researchers said caution should be used in accepting the UC Riverside team’s results.

The main concern seems to be the sweet potato whiteflies used for comparisons. The team of Perring, Arthur D. Cooper, Russell J. Rodriguez, Charles A. Farrar and Tom S. Bellows Jr. used sweet potato whiteflies that had been kept in the laboratory for years. However, since the arrival of the silverleaf fly, the sweet potato whitefly has been virtually eradicated in fields.