Insect ecologist Chelse Prather is "rewriting the textbook" about the role certain minerals might play in controlling grasshopper and other insect populations under a $346,500 National Science Foundation grant.
"[...] this is groundbreaking, rewriting the textbook kind of stuff."
Prather, assistant professor of biology, and four students spent 12 weeks manipulating soil nutrients in a coastal tallgrass prairie south of Houston, Texas. Their goal? To test the nutrients’ importance in determining grasshopper density and diversity.
Grasshoppers are an important part of grassland ecosystems, eating plants and serving as fodder for other animals. But they also compete with livestock for food and in large populations can cause millions of dollars of damage to pastures and rangeland. Ranchers and farmers spend nearly $1 billion annually to control grasshoppers in these areas, but still can't predict their numbers year-to-year.
"This type of information could actually help us predict outbreaks better and has lots of implications for how we manage these systems," Prather said.
Nitrogen and phosphorus are essential elements for plant and animal growth, but these "macronutrients" are now abundant in most soil because of their prevalence in fertilizer. Prather is studying whether less common "micronutrients" such as calcium, potassium and sodium might help determine the structure of grasshopper communities.
In the laboratory, Prather discovered grasshoppers can detect the amount of calcium in blades of grass and actually choose to eat ones with specific levels of these micronutrients. In the field, she found a correlation between the level of micronutrients in plants and the number of grasshoppers in that area.
Under the National Science Foundation grant, Prather is testing her hypothesis using every combination of nitrogen, phosphorus, calcium, potassium and sodium across nearly 29 acres at the University of Houston Coastal Center. For the second year, she and her students spread 10 tons of fertilizer in 128 10,000-square-foot plots, replicating each treatment eight times.
"We are going plot to plot testing grasshopper density, sweep-netting insects and looking at grasshopper diversity," said Kiersten Angelos, a senior biology major.
In summer 2016, Prather saw vast differences in the plant communities in the various plots. Insects also started to respond to the micronutrients — particularly grasshoppers, which responded strongly to calcium and sodium.
"People didn't think that animals like insects were limited by micronutrients, so this is groundbreaking, rewriting the textbook kind of stuff," she said. "It's also showing us that dumping all this nitrogen and phosphorus on the ground has significant effects for how ecosystems function — in particular these grasslands."
Prather hopes her tests will show whether adding large amounts of nitrogen and phosphorus fertilizer to soil has resulted in plants and animals responding differently to other nutrients.
"I think this project will hopefully produce a lot of papers," she said. "We're getting results that are the most exciting of my career."
In addition to her micronutrient work, Prather is researching whether grasshopper diversity affects how grasslands function under a $150,000 grant from the U.S. Department of Agriculture in collaboration with Angela Laws, research assistant professor at the University of Houston. Prather is also part of a team to receive a University STEM Catalyst grant to study grasshopper biomes by tracking decomposition rates and invasive fire ant rates in the region.