SDSU scientists rediscover switchgrass moth in ethanol research
By Lance Nixon, Capital Journal
PIERRE (AP) — It's 2004, and South Dakota State University forage crop breeder Arvid Boe is trying to figure out what insect has been wreaking havoc with his switchgrass plants in an experimental plot at Dakota Lakes Research Farm near Pierre.
The damage is done by larvae of a small, ordinary-looking moth that no one recognizes, and at first Boe's entomologist colleagues suspect it's a species completely new to science.
Then a scientist named David Adamski, one of the country's best experts on this particular family of insect, sets them straight: It's a species first collected about a century earlier, in 1906, and then formally described in 1910: Blastobasis repartella.
But it had dropped out of sight for decades.
In essence, SDSU had rediscovered an insect about which almost nothing was known and then renamed it — at least in layman's terms — with the common name that has stuck ever since: the switchgrass moth.
That one incident could have been a playbook for several discoveries that have followed the same pattern in the years since then. What's driving the work is that forage crop breeders are developing native grassland plants such as switchgrass, prairie cordgrass and cup plant into next-generation ethanol crops, the Capital Journal reported. Making cellulosic ethanol requires breaking down the actual cell walls of a plant — a more complicated process than just fermenting the starch, as with making corn ethanol — and fibrous crops such as the natives grasses of North America would be an ideal feedstock.
But that ethanol work is fueling new research for entomologists as they find themselves learning more about the insect communities that rely on those grasses.
The irony is that insects that have quietly depended on certain plants for millennia, in some cases living parts of their cycles inside the stems of plants that no one ever cared about previously, now find themselves elevated to the status of potential pests.
"With these native grasses, I suspect a lot of these things have been overlooked," Boe said.
For example, Boe and his colleagues went on to discover a species of midge that is even more damaging to switchgrass than the switchgrass moth — and this time the midge is indeed a species previously unknown to science. Scientists have since named it Chilophaga virgati.
"In terms of agronomic growing of switchgrass, the gall midge has probably turned out to be the single most important species that impacts potential biomass production of switchgrass," SDSU entomologist Paul Johnson said. "Until we started this work it was an unknown species to science. It was formally described in 2011. Since then we have been focusing on the life history of the insect. It is a species that seems to be associated with only switchgrass, no other plant."
Johnson and his colleagues are now studying the insect to learn where it lays its eggs and where larvae feed, for example. That could be crucial knowledge if and when switchgrass become a cash crop raised to produce ethanol, since gall midge infestations in the stalk of the plant cause 100 percent loss of seed and 40 to 40 percent loss of seed.
"On top of that, as part of those studies on the life history and ecology of the gall midge, we have found this guild of, so far, three species of parasitoid wasps, one of which so far has proven to be a new species to science," Johnson said.
That new parasitoid wasp was partly described earlier in 2013, Johnson said.
And that's only the start.
Collaborating with forage agronomist Ken Albrecht of the University of Wisconsin, Boe and Johnson have recorded 30 different organisms living in native plane ecosystems. Nearly two-thirds of them had never been identified and catalogued.
The situation is adding a mood of discovery and excitement to native grass research, even though the discovery of the insects is peripheral to the main task at hand — developing new energy crops.
"The aspect of discovery of new organisms, new life histories and associations of different species with each other in communities that had never been documented before, that is fun. That's exciting," Johnson says. "That's a driving force for continuing the work. I like those new fields where absolutely new discoveries can be made, even if they're tiny little insects."
Johnson says it's not surprising that many of the previously unknown insects have been hiding in plain sight.
"These are examples of insects that we would now consider to be grassland- or prairie-specific insects," Johnson said. "Historically grasslands have been some of the most abused ecosystems in the sense that they were well recognized early on as being very fertile. Pioneers, farmers, ranchers, everybody that moved across the continent historically made use of these lands, and they preceded in some cases by a hundred years the scientific investigation of these communities. And these are very small insects. They tended to get overlooked."
Previously, such insects of the native prairie ecosystems tended to come to the attention of farmers in the prairie only when the insects began feeding on farmers' crops.
"For example, there's a cutworm moth whose caterpillars naturally feed primarily on prairie cordgrass, but in the late 1880s and into the 1890s and early parts of the 20th century, that caterpillar became a pest in corn," Johnson said. "That's when attention came to it. It became a pest in corn because at that time a lot of the best lands in Iowa and other states were already being tilled or planted, and so farmers were starting to edge their fields a little deeper into wetlands where prairie cordgrass grows. When that happened, this prairie cordgrass-feeding insect decided that corn tasted good, too. It naturally moved into corn rows that were adjacent to the prairie cordgrass. It never proved to be a permanent pest. It is one of these situations where the encroachment of agriculture disrupted a local ecosystem and at least one species took advantage of a new food source."
Boe said the future could hold similar opportunities for native grass insects to become pests if their host plants become crops cultivated for energy. Boe said he already sees it in his experimental plots.
"I think it's like free popcorn or something," Boe said. "Once the insect finds it, it seems like they settle in and seize the day."
Johnson said the switchgrass moth (Blastobasis repartella) and switchgrass midge (Chilophaga virgati) both reduce tiller biomass in switchgrass — the actual portion of the plant that could potentially be converted to energy — and destroy seed production.
But other insects to worry about in the new suite of energy crops include the cordgrass moth (Aethes spartinana) and the cordgrass bug (Ischnodemus falicus), which can cause devastating reductions in biomass and plant health of prairie cordgrass. Another moth called the giant eucosm (Eucosma giganteana) reduces cup plant bomass that can be harvested.
"All of these pests produce economic injury levels within three years of planting in monocultural agronomic plantings, but are negligible in natural occurrences of each plant species," Johnson and Boe said in an academic paper they co-wrote with Ken Albrecht of the University of Wisconsin and SDSU colleague Veronica Calles Torrez.
Boe said it's too soon to say whether producers growing native grasses to make cellulosic ethanol will need to spray pesticides to control an insect such as the switchgrass midge, or whether they can mimic whatever mechanism keeps insects from being a big problem to their host plants in native prairie. More research needs to be done before scientists can answer that question.
Boe said he and some other forage breeders are exploring the idea of "sculpting the prairie" or "sculpting the landscape" — a concept put forward some years ago by conservationist Erling Jacobson of the U.S. Department of Agriculture's Soil Conservation Service. The idea is that growers could position energy crops where they would grow best in their native landscape instead of planting switchgrass from fencerow to fencerow, for example.
That means that prairie cordgrass would be grown in low, wet areas; cup plant and switchgrass might be grown in the zone above that; and grasses such as big bluestem might be grown in another zone above that.
The plants would still be grown in monocultures, but by different zones on the landscape where plants of those species would tend to establish themselves anyway.
Boe said only research can say whether such a system of zoned monocultures — similar to the way the prairie grows native grasses if left to itself — would reduce insect infestations.
What is clear is that the insects show up in very short time in research plots, Boe said.
But it's also apparent that the research with native plants is showing that a lot of biomass can be produced as an energy feedstock. For example, the cup plant research is achieving remarkable yields.
"We just finished harvesting plots of cup plant that yielded 10 tons of dry matter per acre. Those are the highest-yielding biomass numbers we've ever seen," Boe said.
That makes the cup plant, and the giant eucosma that relies on the plant — all the more important, Boe said. The side benefit is that biologists are learning far more about the interaction of plants and a relatively unknown suite of grassland insects on the North American prairies — and just in time.
"I think it's very interesting, very worthwhile," Boe said. "At the same time, we're talking about the fastest-shrinking ecosystem on earth — the tall-grass prairie."