An entomologist identifying the insects in native grasses is like a kid in a candy store.
"We’re scurrying to beat ourselves, putting out new discoveries,” said entomologist Paul J. Johnson of the South Dakota State University Plant Science Department. SDSU is one of the few research institutions documenting the diversity of insects living on and among native plants like switchgrass, prairie cordgrass and cup plant.
Johnson and grass breeder Arvid Boe have been invited to present their work at the Switchgrass II conference, Sept. 10-12, in Madison, Wis.
Collaborating with Ken Albrecht, a forage agronomist at the University of Wisconsin, Johnson and Boe have recorded 30 different organisms living within native plant ecosystems. Nearly two-thirds of them had never been identified and catalogued.
Impact of insects
Johnson’s presentation will focus on the switchgrass gall midge, a tiny fly that infests the stalk causing 100 percent loss of seed and 40 to 60 percent loss of plant growth, depending on how many stalks, or tillers, of grass are affected.
"Every species of grass has at least one midge in it,” said Johnson. He is examining the life cycle of the switchgrass midge and its relationship to its host plant.
The midge larvae normally spend the winter in the plant tissues, but recently researchers discovered that they are harvested along with the seed when a part of the grain stalk is cut, Johnson explained. Though they don’t eat the seed, the midge could be dispersed to other areas when the seed is subsequently planted.
Potential as a crop
Vance Owens, a professor of plant science and interim director of the North Central Center of the Sun Grant Initiative, said these findings have dispelled the misconception that these native plant species don’t have many natural pests. The important discoveries made by scientists like Johnson and Boe would not have been possible without support from the US Department of Energy Biomass Technologies Office.
Switchgrass is one of the native grasses being considered as an energy crop. The Sun Grant Initiative promotes collaboration among researchers from land-grant institutions, government agencies and the private sector to develop bio-based transportation fuels.
Currently, switchgrass is raised mostly for conservation plantings including erosion control, restoration of wildlife habitat and conservation reserve program. Clint Johnson, owner of Millborn Seeds of Brookings, said a combination of grass species that may include switchgrass is sold for prairie restoration because the diversity helps avoid disease and insect problems.
Ways to minimize damage
The next step will be to measure the midge’s potential impact on switchgrass as a crop. For that, Johnson and Boe will collaborate with researchers in New York, Wisconsin, Oklahoma, Kansas and Mississippi.
Entomologists are now looking at the relationship among different populations of midges to determine whether more than one species is involved. Johnson noted that the genetic coding necessary to figure this out will also give plant breeders the information they need to begin screening native grasses for resistance to insects.
But developing resistance takes time. Until then, “this crop is amenable to a natural biocontrol,” Johnson said.
Natural predators, such as a newly discovered parasitic wasp that feeds on the larvae, may potentially be used to control midge populations, Johnson explained. These wasps could either be collected from a field or reared artificially and then dispersed in grass plots.
Finding ways to minimize damage from insects is an important step toward making switchgrass an agronomically viable crop.
SOURCE: South Dakota State University
Larvae of the gall midge spend the winter in plant tissues such as this switchgrass tiller.
A bin sample of switchgrass seed shows gall midge larvae present that could be distributed when the seed is planted.