Environmental Remediation class studies ivermectin’s effects on plants and insects

The students are Katelyn Christian of Chadron, Kirby Corfield of Brady, Neb., Echo Ecoffey of Rushville, Neb., Val Leone of Fowler, Colo., Talor Morava of Crawford, Neb., Deidra Renkenberger of Ralston, Neb., Colton Rosane of Martin, S.D., and Piper Ryschon of Scottsbluff, Neb.

Kiiskila said he and the students selected ivermectin for their research based on its common use and ease of access.

Rosane, an organismal biology major, based his plant-focused portion of the research on two studies that tracked the uptake and effects of ivermectin in soybeans. Drawing from those findings, he applied similar concepts to native prairie plants by testing three exposure levels: a realistic fecal dosage, a high dosage, and a control.

“In the high-dosage group, plants died within just a few days,” Rosane said. “But even at the more realistic fecal concentration, we saw signs of stress almost immediately.”

Symptoms included yellowing, tissue death, and reduced growth. Upright prairie coneflower and large-flowered penstemon were especially sensitive, while purple prairie clover and showy milkweed managed to survive despite visible stress. Leadplant, blue grama, and buffalo grass showed few early effects but declined noticeably later in the study.

Weedy species like lamb’s quarters, broadleaf plantain, and eastern redcedar, however, were unaffected and even thrived.

“That’s one of the most concerning things we saw,” Rosane said. “The native species were struggling, but the weedy ones kept growing. It could shift the entire balance of a rangeland ecosystem.”

Mosses and lycophytes, key to soil health and water retention, were also highly sensitive to ivermectin exposure.

“We lost most of the moss samples early in the trial,” Rosane said. “They seem to have no tolerance for it.”

Ryschon, who has a double major in biology with a focus in molecular biology and in physical sciences with a focus in chemistry, played a key role in developing methods for the experiment and its completion.

She researched what doses of ivermectin would realistically occur in the environment. She performed calculations to determine a fecal dosage, representing the drug’s transfer from livestock waste into the soil, and a direct dosage simulating runoff from livestock skin.

In addition to designing the dosage system, Ryschon assisted with plant care throughout the trial and took part in measuring and administering each round of ivermectin. Her research focused on microscopic and biochemical analysis of plant and insect samples including moss, grass, soil, mealworms, and grasshoppers. While resource limitations prevented her from using High-Performance Liquid Chromatography (HPLC) to measure ivermectin concentrations, she designed a detailed plan to analyze physical and molecular effects.

Ryschon dissected mealworms and grasshoppers to prepare them for the Scanning Electron Microscope (SEM).

“They were too large to fit in the sample chamber, so I dissected them at the abdomen and analyzed the head and thorax,” she said.

The samples were air dried in petri dishes since the SEM requires zero moisture to take high-resolution images.

Even before completing her tests, Ryschon observed dramatic physical changes in insects. She suspects the drug disrupted their nervous systems.

“Once they were exposed to ivermectin, they became sluggish almost immediately,” she said. “At first, we thought they were dead, but when I picked them up with tweezers, their forelegs would twitch.”

Christian, an organismal biology major with a focus on wildlife management, studied how ivermectin affects arthropods.

“There have been many past studies on the ecological effects of ivermectin on dung beetles,” she said. “But we wanted to examine the wider effects of ivermectin use on the landscape.”

Christian’s work tested the impact of ivermectin on native grasshoppers and domesticated mealworms. The grasshoppers were split into control, fecal-dosage, and direct-dosage groups. The mealworms were grouped by life stage with pupae and larvae receiving the fecal dosage.

“Within two days of treatment, the mealworms became extremely lethargic, five of the fecal-treated grasshoppers died, and the direct-treated grasshoppers appeared paralyzed,” Christian said.

As the study continued, the grasshoppers showed signs of necrosis, had obvious molting issues, and all died.

While the mealworms experienced lower mortality, nearly all of them became sluggish or paralyzed.

“A few larvae were necrotic, and others showed difficulty molting. These symptoms suggest that ivermectin not only interferes with the molting process, which was known from past studies on dung beetles, but may also disrupt the nervous system in insects more generally. From this study, it’s obvious that ivermectin has the potential to interfere with the normal life cycles of many species,” Christian said.

Rosane said the class findings point to the need for more in-depth, long-term studies.

“If we’re weakening native species and promoting weeds without realizing it, we could be undermining the health of these rangelands,” Rosane said.