BioEd Online

Scientists have harvested a virus in order to wipe out a caterpillar that can be fatal to humans.

The caterpillar, which grows into the browntail moth, strikes fear into the heart of entomologists. Simply touching it triggers a severe rash, skin welts and respiratory attacks, and has left two researchers dead in the last century. "It is a really nasty beast," says George Boettner of the University of Massachusetts in Amherst.

Native to certain regions of Europe, the browntail moth sailed into Boston with the ornamental rose trade in the late 1800s. Lacking many natural predators, it quickly spread in the north-eastern states and stripped trees of their foliage, before mysteriously shrinking back to a few coastal pockets by the 1930s.

In the last few years, however, the caterpillar has again reared its head, venturing periodically into Portland, Maine, and the forests of Cape Cod, and raising fears that it will spread further. Because pesticide use is prohibited in protected forests, the outbreaks prompted Boettner and his colleagues to seek a new way of controlling the moth.

Sticky solution

The group hit upon a type of virus called a baculovirus, which naturally infects and kills browntail moth caterpillars in Europe. Researchers have previously struggled to grow this virus because they had to collect it from the toxic creatures in summer while wearing protective suits. "It is not a fun thing to do in 30 °C weather," Boettner says.

Boettner teamed up with James Slavicek of the US Department of Agriculture's Forest Service in Delaware, Ohio. They harvested the virus, mixed it with water and sticky molasses, and squirted the mixture on to individual trees in Cape Cod.

Around 50-80% of the moths were killed by the virus within weeks, Boettner says. Should the preliminary trials hold up, he hopes the virus could be mass produced as an alternative to the harsh pesticides that kill many moth species. It might also treat periodic outbreaks of browntail moth in Europe, he says.

Releasing a virus to combat a moth may raise environmental concerns, as it could infect other species with unknown consequences. But the virus did not infect close moth relatives in the lab, the researchers say. It appears to be activated only by a particular food in the browntail moth's gut.

Researchers are interested in using species-specific viruses to combat other invasive species, such as the gypsy moth, in US forests, Boettner says. "There is probably an insect virus for nearly every insect on earth; it is really an untapped resource," he says.

Boettner discussed his results as part of Expanding the Ark, a two-day symposium in New York City. The meeting is focusing on ways to control invasive species, and is looking at pollution and other factors that are destroying invertebrates.