An ISU entomologist professor has been working with viruses which may be useful tools for farmers in the Midwest plagued by insect pests.

Bryony Bonning is working with baculoviruses, which infect the caterpillars of some moth and butterfly species. Scientists have been able to genetically engineer a baculovirus so that it produces a gene for a scorpion toxin.

This engineered virus is much more deadly to some insect larvae, and it may provide an alternative to chemical insecticides, Bonning said. She also said the engineered baculoviruses are better than normal insecticides because they will reduce the environmental contamination that results from chemical insecticides.

The new insecticides will benefit farmers by providing an alternative approach to pest control. They are not as good as chemical insecticides yet, with future development Bonning said they should improve.

“They are being developed for repeated spray applications and they can also be sprayed using the equipment that farmers currently have, so it’s not like they have to invest in a whole new set of equipment, which is good,” Bonning said.

Bonning is studying a virus that is specific for the larvae of some pest species that exist in Iowa, including the European corn borer, the black cutworm and the cabbage looper.

“Some of those species, like the cabbage looper — it will infect really well, and it will kill the insect very quickly,” Bonning said. “Other insects, like the corn borer, are significantly less susceptible, so you have to spray a lot more virus or else use some kind of agent which will increase the infectivity.”

Because the viruses are specific to moth and butterfly larvae, they will not be effective against other types of insects, such as root worm, a major pest in this area, Bonning said.

“The idea of making viruses that act faster is to create a new agent that is going to be competitive with chemical insecticides, because chemical insecticides are obviously very fast,” she said. “Some research has indicated that if you apply this virus with a very low dose of pyrethroid insecticide, it is better than using the two things alone. Originally, people were thinking these would replace the chemicals, but now it seems like you can significantly reduce the amount of chemicals and get the insects.”

Naturally occurring baculoviruses have existed for millions of years, said Bonning. They are a part of life for the insect species they infect. But one problem with these naturally occurring baculoviruses is that they take from four days to weeks to kill the insects.

“It depends on the environmental conditions, but this amount of time allows for a significant amount of damage that can be done by the insect,” Bonning said. “Hopefully, the recombinant [engineered] viruses will kill within three days or quicker.”

When the virus expressing the scorpion toxin gene is ingested by a target insect, it invades the insect in the same way as the naturally occurring virus, Bonning said. The toxin gene is then expressed until there is enough of the toxin to kill the insect.

“It won’t happen immediately unless you have a very effective toxin,” she said. “The toxin we are using is one tiny component of the scorpion venom mixture, which we know is not toxic to humans,” Bonning said. The toxin appears to be specific to insect nervous systems.

In 1994, environmentalists objected to field tests of the engineered baculoviruses in England, although scientists followed all the regulations needed to perform such tests. Some of the environmentalists’ concern was because the field test sites were less than half of a mile from a sensitive ecological haven called Wytham Woods.

In the United States, there was no objection when American Cyanamid Company of Princeton presented a proposal to do the field trials, Bonning said.

The trials have been performed in “five to 10 states now,” she said. “The virus is safe, the toxin is safe, as far as mammals and non-target animals [are] concerned.”

Bonning began doing research at ISU in October of 1994. She received her Ph. D. from the University of London, where she worked at the London School of Hygiene and Tropical Medicine studying the molecular biology of baculoviruses. She did two years of post-doctoral work at the Institute of Virology at Oxford University. She then came to the United States where she did four years of post-doctoral work on viral insecticides at the University of California Davis.