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Insect-Killing Virus Gets Faster Punch, May Help Protect Crops

July 3, 1991

NEW YORK (AP) _ A virus that kills crop-destroying insects has been genetically modified to act faster, boosting its promise for protecting crops from insect pests, two new studies say.

The virus killed faster or paralyzed before killing when it was given genes to let it secrete insect-targeting toxins, researchers said.

The paralysis-inducing version gave insects 40 percent to 50 percent less time to chew plants than the natural virus, said researcher Lois Miller.

Miller, a professor of entomology and genetics at the University of Georgia in Athens, and co-author Michael Tomalski present their work in Thursday’s issue of the British journal Nature. A second paper details work by British researchers with a different gene.

Viruses called baculoviruses are one biological approach under study as scientists look for alternatives to chemical pesticides.

The two new papers ″take the development of effective ‘biopesticides’ a long step further,″ says a Nature editorial by Michael Hochberg of Imperial College in Silwood Park, Berkshire, England, and Jeffrey Waage of the International Institute of Biological Control in Silwood Park.

The notion of controlling insects by using germs harmful to them has attracted particular attention of scientists, partly because the germs target only the insects, Hochberg and Waage wrote. But germs developed so far often break down quickly on plant surfaces, they may be costly to produce, and they kill slowly in comparison to chemical insecticides, they said.

Baculoviruses take four to eight days to kill, and ″that’s a bit longer than you can wait″ as the insects continue to eat crops, Miller said in a telephone interview.

Five types of baculovirus are now registered with federal regulators as pesticides, and in all perhaps 30 or 40 kinds might be useful for protecting such crops as cotton, corn, alfalfa, soybeans and vegetables, Miller said.

The main target is the caterpillar-like larvae of certain insects, she said.

Her research used the cabbage looper, which attacks vegetables such as broccoli and cabbage. Researchers gave the virus a gene to let it secrete a toxin that paralyzes insects. The gene came from a species of mite that injects the toxin into its prey.

The toxin does not affect people or other mammals, Miller said.

She also said people would not have to worry about food from virus- protected crops because the food would contain the gene rather than the toxin, and people eat many virus and plant genes already in their food. The toxin itself degrades quickly in the environment, and if it somehow reached a person intact it would be destroyed in the stomach, she said.

In her study, 93 percent of cabbage looper larvae injected with the altered virus were paralyzed within two days, while the rest were dead from the trauma of the injection. In contrast, the natural virus yielded a total of 13 percent dead within two days, with all dead in four days.

In another experiment, more than 80 percent of larvae that ate the altered virus were paralyzed or dead by the fourth day, compared with only about 10 percent that ate the natural virus.

The British study used a toxin gene borrowed from a North African scorpion. Half the larvae that ate the altered virus were dead within about 86 hours, compared with 113 hours for the natural virus. Other experiments showed that the amount of leaf eaten by the larvae was cut about in half when the altered virus was used, the researchers said.

The British work was done by scientists at the National Environmental Research Council Institute of Virology and Environmental Microbiology in Oxford, and Wellcome Enviromental Health in Berkhamsted, Hertfordshire.

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