By Sean Henahan, Access Excellence

ATHENS, GA- A genetically engineered virus producing a toxin found in scorpions has proven to an effective killer of cotton bollworms and tobacco budworms in the first field test conducted in the US, report researchers at the University of Georgia.

The baculovirus, which contains a gene encoding for an insect-specific toxin found in scorpions, killed virtually all the bollworms and budworms exposed to it. This baculovirus by design affects only targeted insect species, with no effect on humans or other wildlife.

"The use of microbial pathogens to control insect pests has been proposed for years, but, until recently, only limited industrial effort has been devoted to their development. The intimate relationship that virus pathogens must have with their hosts can provide the most precise means of targeting specific insect pests for population control, thus protecting beneficial insects and other organisms in the ecosystem," said Dr. Lois Miller, a pioneer in the field of baculoviruses at the University of Georgia.

The tests were conducted on small field plots near Athens, Georgia, this summer, using procedures approved by the Environmental Protection Agency. The researchers sprayed the baculovirus on cotton plants. The tests proved for the first time that a genetically engineered toxin-expressing baculovirus can be used in the field with results that rival or surpass other biological insecticides.

Previous attempts to utilize viral insecticides have been unsatisfactory since they worked too slowly to be efficient in the field. In earlier laboratory and greenhouse tests (and in nature), the baculoviruses had been taking anywhere from five to seven days to kill target pests. Worse, target insects exposed to the natural baculoviruses actually ate more before they died than those not exposed, probably due in part to a mechanism in the baculovirus which tries to keep its host alive for as long as possible.

"We found a way around that several years ago when we deleted a gene in the baculovirus This enables us to decrease the amount of time it takes for the virus to be lethal to its host," said Miller.

Miller's laboratory also found strains of the baculovirus that acted faster, and she began inserting toxin genes that produced a toxic effect when expressed by the baculovirus. Toxins tested included those from mites and scorpions. The scorpion toxin proved most effective.

"Baculoviruses are safe because they have co-evolved with their insect hosts over eons. Mutations of viruses occur in nature all the time, but to survive, they must have properties that make them better competitors than what's out there at the time. Thus, genetically engineered baculoviruses would be poor competitors with natural ones Also, engineered baculoviruses don't have enough time to reproduce efficiently, so they are unable to survive. In addition, baculoviruses only affect a very limited number of insects, mostly test species of arthropods," noted Miller.

The tests at the field site this summer compared a biological insecticide called Bacillus thuringiensis (Bt), two different formulations of baculovirus with the scorpion toxin gene inserted and a gene-deleted form of baculovirus. The new genetic insecticide appears as good or better as Bt, which has been in use as a biological insecticide for years, Miller said.

No effects were observed on non-target insect and spiders. In particular, tests confirmed that honey bees and other beneficial insects were not affected.

For now, the genetically engineered baculovirus will probably not replace commercial pesticides, which typically kill a wide range of pests virtually on contact. But with environmental concerns mounting and federal re-labeling requirements for pesticides under way, baculoviruses could provide an additional tool to manage insect pests in a safe, effective way.

Some scientists worry that over time, insects may develop resistance to genetically engineered baculoviruses, but Miller said it would take farmers applying them in large amounts for more than a quarter century for that to happen.

Miller said she remains confident that "thoughtfully developed and tested" genetically engineered baculoviruses can be safely used for the specific control of pest species.

"It is a major advance for a baculovirus to kill insects this fast and this well. I was skeptical of how this would work, to be honest, but now I'm an enthusiastic supporter of the idea, said Dr. John All, a professor of entomology at the University of Georgia.

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