SDSU leads pest research

Erin Beck

Research in the Entomology Department has proven that the sky is the limit. Dr. Paul Johnson, a professor in the plant science department, is in the process of investigating two different insect species, one of which was discovered as recently as 2008 at SDSU.

Both insects are major pests of switchgrass. The switchgrass moth was originally discovered in 1906 near Denver, Col. Nothing was known about the moth aside from the fact that it existed.

Johnson believes this research holds a lot of potential as switchgrass becomes more seriously considered for use as a biofuel source. SDSU is currently the only university carrying out in-depth research on switchgrass pests.

In 2004, Dr. Arvid Boe, another professor in the plant science department, was working with switchgrass when he realized something was damaging the grass in his experiment. After finding that the moth feeds only on switchgrass, the connection between the insect and the switchgrass was made.

“Looking at the agronomic potential to grow switchgrass as a biofuel started the whole thing,” Johnson said.

Johnson became involved with the project in 2006. The goal is to map out the moth’s life cycle and determine its relationship to the plant. The damage the moth is causing to switchgrass will then be better understood.

Johnson and his graduate students have already made significant headway in plotting the moth’s life cycle. During the winter the caterpillar feeds on new buds that grow on the stem below ground. In the spring the caterpillar moves up into the stem at ground level, feeding on and killing the plant when it reaches the three-leaf stage.

When the caterpillar has finished its feeding stage, it forms a cocoon and pupates in the stem. The adult moth emerges from the hole it made in the stem when it first began entering the plant as a caterpillar. The combination of the moth boring a hole through the stem and feeding on the inner tissues is what kills the switchgrass plant.

“We’ve gone from rediscovering a tiny white moth that no one knew about for almost 100 years to this complex relationship with the switchgrass and the parasite,” Johnson said.

Graduate student Veronica Calles Torrez is blazing a trail in entomology as she studies the switchgrass midge, the insect discovered at SDSU. Since she is the first one to carry out an in-depth investigation on the insect, she has very little to base her research off of so far. By taking seasonal soil samples and comparing different plots of switchgrass, she is beginning to piece together the midge’s life cycle.

According to Torrez, the midge larvae feed at the top of the stem at the base of switchgrass’ flower clusters. This prevents seed development and hinders the plant’s reproduction. More research is required to fully grasp a more detailed account of this new species.

“I think it’s important because we can tell farmers that we have this insect and this insect causes this damage,” Torrez said.

According to Johnson, both pests are leaving a noticeable impact on switchgrass production.

“The moth and the midge produce a fairly significant loss in biomass and seed production by their combined efforts,” he said.