Invasion of The Superbug

By MICHAEL D. LEMONICK

By this time of year, fields in the Imperial Valley, which straddles the California-Mexico border, should be bursting with ripe melons ready for shipment to markets around the U.S. Instead, 95% of the fall crop has been lost and much of the rest lies rotting on the vine. Harvests of lettuce, broccoli, cauliflower, squash, citrus fruits, table grapes, sugar beets, carrots and cabbages are threatened as well. Total crop losses in Imperial County and nearby Riverside County have already reached $90 million. Says melon grower Ben Abatti, who has been farming in the area since 1956: "It is total disaster."

The agent of disaster is a 3-mm (one-tenth-in.) insect known to scientists as the poinsettia strain of the sweet-potato whitefly but to farmers as the Superbug. Millions of these voracious insects have spread over the Imperial Valley, massing on the undersides of leaves and sucking plants dry, weakening or killing them in the process. Farmers first noticed the flies getting worse in July, and by September swarms of them looked like white clouds. They covered windshields and got stuck between people's teeth. Farm workers had trouble inhaling and eventually had to wear masks. Not since the Mediterranean fruit-fly scares of the early and late 1980s has California's $18 billion agriculture industry, which during winter supplies close to 90% of the fresh produce in the continental U.S., been so alarmed by a pest.

The first hint of a visit by fruit flies is invariably met with quarantines . and airborne-insecticide spraying campaigns. The new Superbug has no effective native predators in California, and pesticides are largely useless against it. If it continues unchecked, Imperial Valley could be put out of business for months. That could cause an estimated $200 million in farm losses by spring and higher prices at the produce counter. The wholesale price of melon has tripled, and by one reckoning, the average cost of a head of lettuce in a supermarket could go from $1.19 to about $1.50. In some areas, these foods may be in short supply.

California farmers have been fighting other types of sweet-potato whiteflies for years. But the poinsettia strain, so named because it first appeared in the U.S. on poinsettia plants in Florida greenhouses, reproduces twice as fast as its relatives and consumes five times as much food from its victims. It comes originally from somewhere halfway around the world, possibly Iraq or Pakistan, and apparently reached America in 1986, probably hidden away in a cargo shipment.

Florida is a little too cool and rainy, on average, for the Superbug's taste, and the infestation there was never as serious. But when the fly arrived in Southern California, probably in a fruit basket or vegetable shipment, it felt right at home in the dry weather and summer temperatures that can reach 46 degreesC (115 degreesF). Because the insect is happy eating some 500 varieties of plants (one of the only vegetables it doesn't seem to like is asparagus), it found the fertile Imperial Valley to be a veritable smorgasbord.

Since all pesticides approved for use in California have been ineffective against the bug, the best advice agriculture officials can give is for farmers to plow under devastated fields, denying the pests their food sources. In addition, roadways and ditches around the valley are being cleared of weeds that help sustain the whitefly. Farmers are considering a "host-free" period in which they will do no planting at all. Says John Pierre Menvielle, who farms 900 hectares (2,200 acres) in Calexico: "If that is what it takes, we will do it."

One possible long-term solution, says Nick Toscano, an entomologist at the University of California at Riverside, is a tiny stingless wasp that lives in the California desert. It lays eggs on the immature whitefly, and when they hatch, the baby wasps eat the fly. Other researchers are cross-breeding the poinsettia whitefly with more innocuous varieties in hopes of developing a mild-mannered hybrid that might displace the Superbug. In the next six or nine months, a team of scientists will leave for the Middle East in search of a parasite from the fly's native habitat that could combat it. A promising natural pesticide is neem-seed extract from the Indian Azadirachta indica tree. The bugbusters may have to resort to synthetic insecticides that are not approved in California but may have to be -- in a hurry.

Unfortunately, that last option could end up causing more trouble in the long run. The toughness of the poinsettia whitefly has evolved over generations. "It has been exposed to pesticides for a long period of time and developed resistance," explains Toscano. Using new pesticides could halt the bug's advance for now -- but given its ability to adapt, the result could be some sort of Ultimate Bug that would make Superbug look tame.

With reporting by Jeanne McDowell/Los Angeles