Species interactions in prairie strips: Reflections from an LTER Fellow

Graduate researcher, Alice Puchalskyis a Ph.D. student in Dr. Nick Haddad’s lab at Michigan State University. Her research focus is on moths, butterflies, and interaction networks.

caterpillar with parasitoid eggs
An unfortunate caterpillar hauling parasitoid eggs around on its back.

When I began graduate school, I did not imagine myself eagerly watching a caterpillar writhe around in a plastic cup, wondering about its fate. But, that is where I found myself this past summer. I also did not imagine the delight I would feel in checking on that caterpillar the next day and finding that approximately 30 very small parasitic flies had emerged from that caterpillar’s body. I was hoping that my unlucky, parasitized caterpillar might provide a clue about how to solve two of the world’s most pressing problems: how to preserve biodiversity and feed a growing human population. 

Agriculture makes up about 40% of land use, and this number is projected to increase as a growing human population requires more food. Intensive agriculture – which too often destroys habitat and pumps the environment with harmful pesticides and fertilizers – is one of the main drivers of current biodiversity declines. Biodiversity loss will have many consequences, including declines in the ecosystem services that we rely on such as pollination, pest control, and soil carbon sequestration. So we are left with a paradox: we rely on biodiversity to grow food, and yet our current model of agriculture destroys biodiversity. How can we resolve this paradox in order to both protect biodiversity and feed the world?

One part of the solution may be diversified agriculture. This relies on several practices that increase biodiversity, such as the use of cover crops, growing more types of crops, or the installation of non-crop habitat into crop lands. Increasing diversity within agricultural areas could also increase the number of different interactions between species, known as interaction diversity. By measuring interaction diversity, ecologists can get a picture of which species in an ecosystem rely on each other. Picture a food web: species rely on other species in the food web for their food source. The same is true for other types of interactions – many flowers rely on pollinators to assist them in their reproduction. 

By visualizing or measuring interactions between species, ecologists can determine how complex an ecosystem is and how resilient a system is to disturbances. It is important to consider interaction diversity when implementing new conservation strategies because interactions between species often generate ecosystem functions and services. For example, pollination interactions between bees and fruit trees generate fruit and predation by birds on caterpillars could control pests in a crop field. Biodiversity includes not only the number of unique species, but also interactions between species. As we aim to make agriculture more biodiversity friendly, it will be important to consider species interactions, too. 

Prairie strips at the KBS LTER
Undergraduate researcher, Jessica Meister, working in the prairie strips at the KBS LTER.

In 2019, we began an experiment at the KBS LTER to examine the efficacy of one method of diversified agriculture– prairie strips. Prairie strips are an agricultural conservation practice in which a strip of native prairie plants is installed into a row crop field, usually in the center of a field. Previous research has shown that prairie strips provide ecosystem services like reduced erosion and nutrient loss. Previous work has also shown that prairie strips increase the abundance and diversity of pollinators and pest-controlling insects.  So we know that prairie strips increase diversity for some groups, but we do not know how prairie strips influence communities of organisms and how they affect interactions between species. 

When prairie strips were introduced into the LTER, I saw an opportunity to investigate how prairie strips in row crops influence the abundance and diversity of interactions between species. Particularly, I was interested in the parasitic interaction between caterpillars and their wasp or fly parasitoids. Caterpillar-parasitoids interactions in agricultural settings potentially play an important role in controlling populations of caterpillar species which can be damaging crop pests. Not only did studying caterpillar-parasitoid interactions in the LTER provide a chance to examine how prairie strips influence pest control services, I had the chance to determine if prairie strips increase biodiversity, as measured by the interaction diversity between caterpillars and parasitoids. 

This past summer, I set out to answer my questions by collecting caterpillars from crop fields with and without prairie strips. When I found a caterpillar, I brought it to a field lab where I then reared the caterpillar on it’s preferred food plant until it pupated or a parasitoid emerged. My experience rearing caterpillars for parasitoids was some of the gnarliest and most rewarding work I’ve done as an ecologist. I spent the summer feeding caterpillars, waiting with a twisted sense of excitement and suspense, to see which caterpillars would have parasitoids literally chewing their way out of the caterpillars’ bodies. It was in this context that I found myself delighted to find 30 small flies had emerged from one caterpillar’s body. I am still waiting on the last of my caterpillars to finish their lifecycle– they are currently overwintering as pupa– to determine if they have parasitoids. When the last of my caterpillars have become adult moths and butterflies, I will have the data to determine how prairie strips affect interaction diversity and pest control services in agricultural settings. Potentially, prairie strips could provide a refuge for biodiversity in agricultural areas while providing increased ecosystem services to enhance our food production.