Mantid Research Answers – and Poses – Questions
LEXINGTON, Va., March 26, 2013 – Over the summer, researchers at VMI and Washington and Lee University began delving into a unique line of research that will seek to determine the role that the praying mantis plays in area ecosystems.
Maj. Pieter deHart, assistant professor of biology, and Larry Hurd, Herwick Professor of Biology at W&L, combined their knowledge and expertise to establish a lab population of mantids and determine elements of their diets by analyzing proportions of carbon and nitrogen in their bodies using an isotope-ratio mass spectrometer.
“As with all science, we answered a few small questions and posed dozens more,” said deHart. “We’ve laid the groundwork for moving this forward for many years in the future, which is great.”
Analyzing the diet of mantises will give an idea of what role they play in the ecosystem and how they affect the populations of their prey species, which include both herbivorous insects like crickets as well as carnivorous insects like spiders and other mantids. The ability of mantids to consume other predators puts them at a high trophic level: a few links up the food chain from most other insects.
“We’re really interested in what effects mantids have on the ecosystem, given that they are a very high-level predator. No one has really established what they eat in the wild,” said deHart. “They may be controlling other populations of insects, or they may just be another player in the grand scheme of things.”
In addition to preying on insects, mantids are known to feed on pollen. Research done by Hurd determined that mantids feeding solely on pollen can grow and develop normally, albeit at a slower rate.
“We know that this is possible in the lab, but one of our goals is to discover how much this is actually occurring in the wild,” said deHart. “The main way we can address all these questions is by looking at stable isotopes. That is, finding the biochemical composition of tissues and comparing that with their prey sources.”
Around 200 samples were sent to the isotope ratio mass spectrometer at the Central Appalachians Stable Isotope Facility in Frostburg, Md. DeHart is currently sifting through the results to find meaning in the data, comparing results from mantids raised in captivity to those found in the wild.
“We want to find out in what scenarios they will switch their diet,” said deHart. “The even bigger picture is if environmental conditions change with global climate change, is this something that we’re going to have to worry about?”
It is likely that mantids are playing an important role in balancing other insect populations, and if their diet preferences change due to environmental changes, that could have a significant impact on a given ecosystem.
“So, in the lab we’re raising these things; they’re eating a certain diet, and we can select from those populations and run them for their own biochemical compositions,” said deHart. “We have a very controlled setting in the lab, and we know what their carbon and nitrogen isotopes look like. We can compare that whole picture with the samples we’re getting from mantids in the wild.”
Results so far are promising. At the outset, the concern was that there wouldn’t be enough variation among samples to provide insight into the predators’ behavior, but already results are showing major differences depending on environmental variables.
“One of the things we found thus far is that there is a large variation in their diet in the wild,” said deHart. “You can clearly see trophic level, or food-chain, distinction of prey items in captivity, and we’re seeing distinction in the wild so they’re falling into different groups according to region or time of year.”
In the future, deHart would like to use a more advanced method of spectrometry that not only measures levels of nitrogen and carbon, but hydrogen and oxygen as well.
“The more information we have on each sample, the more we’re going to be able to piece together these puzzle pieces,” said deHart.
The line of research is likely to provide years of opportunities for interested cadets to participate in field and lab work. It is currently supported through grant-in-aid funding, and deHart is applying for a Jeffress Memorial Trust Award to further the research. That award would fund a collaborative project with math professor Maj. Geoffrey Cox.
“It’s our full intention to establish another lab population this spring and into the summer,” said deHart. “I would definitely like to get cadets engaged in this project. The possibility for involving cadets in this research and expanding our research endeavors is just huge.”
–John Robertson IV