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written by: Benjamin P Gregory Over the past few years, a number of reports have shaken the entomology world by indicating that insect populations are declining globally at an unprecedented rate. Dubbed the “insect apocalypse” by the media, this decline in insect population raises a number of serious concerns for the biosphere. Insects make up the foundation of many food chains, and are fundamental to ecosystems all over the world. So why is this decline happening? Among many drivers, pesticide use is very significant. Pesticides can be helpful tools for reducing populations of harmful insects, like those that feed on our crops or spread diseases. But for all of their strengths, pesticides often lack precision, and their broad application kills all insects, including beneficial species that provide important ecosystem services. So how can we control harmful insects while also conserving beneficial species and protecting our ecosystems? That’s where conservation biological control agents come into play. Conservation biological control agents (CBCAs) are species that naturally control the populations of pest species as predators or parasites. CBCAs potentially represent a more sustainable method for keeping our agriculture and public health safe from dangerous insects. Dragonflies are an exciting prospect for biological control, as they are arguably the most successful predators in the animal kingdom, using their incredible aerial speed and maneuverability to intercept and eat a wide variety of flying insects in mid-air, including stable flies, noctuid moths, mosquitoes, and more. Importantly though, dragonflies spend the majority of their lives as aquatic nymphs (known as naiads). This means that, in order for dragonflies to control pest populations on land, they need freshwater habitats like ponds in which to breed and develop. Ponds are fairly common in agricultural systems because they are used for irrigation and stormwater management. This led Amanda Brucchieri, master’s student at the University of Maryland’s Department of Entomology, to ask whether farm ponds promote biological control of agricultural pest insects by providing habitat for dragonflies. She focused on cattle pasture systems, where arthropod pests like stable flies cause $2.26 billion in losses annually.  Figure 2: A dragonfly nymph (Aeshna cyanea) in its aquatic habitat. Image from National Geographic To address this question, Amanda chose 15 farm ponds across Southern Maryland and surveyed them extensively for nymphal dragonflies. She also took measurements of important habitat characteristics like water quality and vegetation composition along the pond perimeter, and tracked adult hunting behaviors above cattle herds.
After meticulously identifying over three thousand nymphal dragonflies, Amanda found that ponds that were more intensively managed (i.e. vegetation removed and grass mowed regularly) had higher overall dragonfly abundance. But more dragonflies doesn’t necessarily mean better biocontrol–certain species are more beneficial than others. It turns out that a plant community made up of trees and grasses along pond perimeters corresponded to higher abundances of beneficial species, like those in the genera Plathemis and Ladona. These species also seemed to prefer larger ponds. In contrast, lightly-managed ponds, whose vegetation was more dominated by vines, hosted fewer beneficial species. In her behavioral surveys, Amanda found that adult dragonflies were more abundant over managed ponds, and that adults flying over cow pastures were indeed foraging on flies. Amanda’s research demonstrates that dragonflies can successfully utilize farm ponds as reproductive habitats in the context of active cattle pastures, and that they exhibit behaviors consistent with conservation biological control. By identifying the characteristics of farm ponds that create habitats for the most ecologically beneficial species of dragonflies, this research provides invaluable guidance for farmers looking to reduce pest populations in a sustainable and cost-effective way. By managing farm ponds for a healthy and native assemblage of plant species at the perimeter, and building larger ponds, farmers can reduce the harm that comes to their cattle herds from pest flies and other insects, while supporting local native ecosystems at the same time. Amanda earned a Bachelors of Science degree in Organismal Biology from Kent State University. Since joining the Lamp Lab in the Fall of 2022 Amanda has been researching the characteristics of farm ponds that can be managed to promote dragonflies as conservation biological control agents in agroecosystems. During her time at UMD Amanda has served as a TA for Freshwater Biology (BSCI 467) and Insect Apocalypse: Real or Imagined (BSCI145). She is also the current President of the Entomological Student Organization, ESO and was the Social Chair for the 2023-2024 term. Further reading: Raebel, E.M., Merckx, T., Feber, R.E., Riordan, P., Thompson, D.J., Macdonald, D.W., 2012. Multi-scale effects of farmland management on dragonfly and damselfly assemblages of farmland ponds. Agriculture, Ecosystems & Environment 161, 80–87. https://doi.org/10.1016/j.agee.2012.07.015 Comments are closed.
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