South Dakota State researchers discover long-ignored moth, new fly munching on switchgrass

Researchers discover switchgrass-hungry moth, fly

SIOUX FALLS, S.D. — Researchers at South Dakota State University have rediscovered a long-ignored moth and found a new fly, both of which like to munch on switchgrass, a crop billed as a future feedstock for next-generation ethanol.

SDSU entomologist Paul Johnson said it’s too early to determine the insects’ effect on future fields of energy crops, but elevating the native plant to crop status could also give the bugs pest status.

Johnson said the moth seems to be relatively widespread and is present in all of the planted switchgrass fields that have been investigated. If insects cause even a 5 to 10 percent biomass loss on standing crops, that could be significant, he said.

“From what we’ve seen there’s potential for significant loss here,” Johnson said. “We just don’t have good numbers yet that are tallied up to actually give estimates on what that loss would actually be.”

The tiny moth — a large adult reaches just 8 to 9 millimeters — was first discovered in Denver in 1910 by entomologist W.G. Dietz, who was using an electric lightbulb to collect specimens.

It’s been virtually ignored for 100 years until SDSU researchers found larvae of an unidentified insect responsible for losses on a private farm in 2006.

They collected an adult male in 2008 and sent it to David Adamski, a research associate with the Smithsonian Institution, who matched it and another moth found in Illinois to the “blastobasis repartella” species.

Adamski, Johnson and SDSU agronomist Arvid Boe are co-writing a paper on the moth to be released this year, but Adamski said a lot more research is necessary to gauge the insect’s effect on switchgrass plots.

“We don’t know if we can even call it a pest,” Adamski said Monday. “Just because it exists, (it) doesn’t mean it’s a pest.”

SDSU researchers also found a new fly they call the switchgrass gall midge. The fly feeds at the base of the developing inflorescence, so it ends up killing the entire flowering structure on the grass.

“It destroys the seed crop, so there is no seed to harvest,” Johnson said.

Johnson said much of the early literature on developing native grasses for use in biofuel stated that the crops had no significant pests. That didn’t make sense from an entomological perspective, he said.

“For all intents and purposes, there is no such thing as a plant that does not get eaten by something,” Johnson said.

South Dakota State researchers will use the upcoming growing seasons to determine how annoying the insects could become for farmers. They’d like to know how quickly a field gets noticed by the insects, their rate of infestation and the possible losses of biomass.

Johnson said he hopes growers don’t have to use many chemicals to control potential pests, which could offset the value of growing native grasses for energy.