Weather radar records drastic drop in mayfly populations

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At the beginning of each summer, mayfly larvae emerge from bodies of water and shed their skin to become full-fledged mayflies, similar to how caterpillars become butterflies. Then, all at once, a swarm of these insects fly away together to reproduce, acting as an important component in the food chain for birds. 

Researchers at the University of Notre Dame, University of Oklahoma and Virginia Tech applied radar technology, the same used for meteorology, to quantify the number of mayflies that emerged annually from two different bodies of water: the Upper Mississippi River and the Western Lake Erie Basin. Their goal was to characterize the size of these swarms using the same technique a meteorologist would use to quantify the amount of precipitation that may fall from a cloud. 

Pulling radar data from the two locations over a span of eight years, the research team estimated that up to 88 billion mayflies can swarm from each location annually. 

“Approximately 88 billion mayflies equate to about 12 trillion calories in the food web, feeding about 54 million baby birds. Therefore, we can assume these insects have a nearly instant impact on the birds that survive off of them when they descend upon their respective shorelines,” said Phillip Stepanian, assistant research professor of civil and environmental engineering and earth sciences, lead author, and affiliated member of Notre Dame’s Environmental Change Initiative (ND-ECI). 

Although the initial study was only intended to quantify mayfly swarms, researchers found more than a 50 percent decrease in population from 2012 to 2019 in these two Midwestern water bodies. Study co-author Jennifer Tank, the Ludmilla F., Stephen J. and Robert T. Galla Professor of Biological Sciences and director of ND-ECI, shared that the next steps are to investigate whether declines like this are widespread, and what may be causing such reductions in the mass emergence of this species of mayfly.

“Other studies have suggested that declines in water quality caused by nutrient and sediment runoff, as well as warmer temperatures, may be impacting mayfly survival,” said Tank. “These mayflies may be our 'canary in the coal mine' in that they’re sending us a message about how tightly land and water are linked regarding the impact of multiple stressors.”

Study co-authors in addition to Stepanian and Tank are Sally A. Entrekin, associate professor of entomology at Virginia Tech; Jeffrey Kelly, professor of biology and director of the Plains Institute at the University of Oklahoma; Djordje Mirkovic, research scientist at the National Oceanic and Atmospheric Administration; and Charlotte E. Wainwright, postdoctoral research associate of civil and environmental engineering and earth sciences at Notre Dame. The study was funded by the National Science Foundation.

To read the full study, visit https://www.pnas.org/content/early/2020/01/15/1913598117

Contact: Brandi Wampler, research communications specialist, Notre Dame Research, brandiwampler@nd.edu, 574-631-8183, @UNDResearch

Originally published by Brandi Wampler at research.nd.edu on Jan. 29.