Insects and Public Health: Bridging Knowledge and Application

written by: M. Rho Ma

​Insects are both essential to ecosystems and a source of challenges for human health and agriculture. They pollinate crops, serve as food for other species, and contribute to nutrient cycling, but they can also act as vectors for diseases or suffer population declines due to human activity. Striking a balance between conserving beneficial insects and managing harmful ones is a pressing concern in entomology. The following research-in-progress talks by graduate students demonstrate how entomological research bridges the gap between ecological understanding and practical solutions, focusing on pesticide impacts, mosquito adaptation, and disease surveillance.  

​Michael Adu-Brew: Evaluating the Risks and Toxicity of Pesticides to Monarch Butterflies and Beyond 
 
Michael Adu-Brew (he/him), a second-year MS student in the Krishnan Lab, explored the unintended consequences of pesticide use on non-target insects, using monarch butterflies (Danaus plexippus) as a model species. Monarchs, iconic pollinators of North America, happen to also be the part of the most diverse family of butterflies, Nymphalidae. Because of that, they can represent a broader crisis: many Lepidopteran species are listed as endangered by the International Union for Conservation of Nature (IUCN) [1] and as of December 10th, 2024, the U.S. Fish and Wildlife Service announced they would be proposing protection of Monarchs under the Endangered Species Act [2].

​This status reflects the vulnerability of many beneficial insects whose growth, development, and survival are increasingly threatened by human activities [3]

Figure 1: A monarch butterfly photo from the Krishnan Lab website. Photo taken by Dr. Krishnan’s colleague, Jacqueline Pohl, at Iowa State University.

One significant threat to insects is pesticide application. In fact, the U.S. Environmental Protection Agency (EPA) announced a policy in 2022 requiring new pesticides to undergo evaluations under the Endangered Species Act (ESA) to assess their potential impacts on threatened and endangered species [4]. This policy ensures that pesticide approvals incorporate measures to protect vulnerable wildlife and their habitats, supported by research on the impacts of pesticide application.
 
To better understand different pesticide application methods and their associated tradeoffs, Michael Adu-Brew conducted research aimed at assessing the toxicity and risk of four newer chemical insecticide classes and two biological fungicides on monarch larvae. The study involved topical and dietary toxicity bioassays, generating dose-response curves to evaluate the impacts of each exposure route on caterpillar survival. He reared monarch caterpillars for these bioassays—observing the caterpillar’s transition to a pupa and ultimately, adult butterfly. Additionally, Michael sought to estimate spray drift exposure and assess the risks associated with foliar pesticide applications, with a specific focus on larval mortality at varying distances downwind from treated areas. This comprehensive approach provided a detailed evaluation of how different pesticide types and application methods affect monarch larvae, offering critical insights into mitigating risks to non-target species.
 
The results, which he recently presented at the 2024 Entomological Society of America (ESA) meeting in Phoenix, Arizona, revealed a ranking of toxicity among the pesticides tested. Biological fungicides, afidopyropen, and sulfoxaflor exhibited relatively low toxicity, while cyantraniliprole showed medium toxicity. Broflanilide emerged as the most toxic, falling into the high-toxicity category. Both topical and dietary exposure routes negatively impacted larvae, causing reduced growth, developmental delays, and hemolymph loss, with dose-response effects varying across exposure methods. These findings emphasize the need for careful consideration of pesticide types and application methods to balance effective pest control with the conservation of beneficial insects. 

Figure 2: Michael Adu-Brew presenting at the 2024 Eastern Branch ESA meeting in Morgantown, WV. Photo taken from the Krishnan Lab website.

Looking ahead, Michael plans to complete these preliminary studies, refine dose-response curves, and further assess pesticide risks using the exposure model AgDRIFT. Additional research will include toxicity studies on the Eastern-tailed Blue Butterfly, serving as a surrogate for the second most diverse family following Nymphalidae: the Gossamer-winged Butterfly (Family Lycaenidae) species. This will broaden the understanding of pesticide impacts on other vulnerable insect groups. Michael’s work continues to bridge the gap between effective pest management and biodiversity conservation.

Michael completed his undergraduate education in Kumasi, Ghana at the Kwame Nkrumah University of Science and Technology (KNUST). He was originally drawn to Medical Entomology and eventually found himself interested in the effects of pesticides on non-target insects. In conducting this research, he has developed a soft spot for Lepidopterans. To connect with Michael, check out his LinkedIn. Fun fact: Michael is the reigning ping pong champion in the Entomology department.

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Figure 3: Photo of Ben Gregory, courtesy of Ben Gregory.

Ben Gregory: Local Adaptation of Mosquito Larvae to Thermal Stress  

​The second talk, presented by third-year doctoral student Benjamin Gregory (he/him) from the Fritz Lab, investigated the geographic distribution and thermal adaptations of the mosquitoes Culex pipiens and Culex quinquefasciatus, two major vectors of West Nile virus (WNv). These species occupy distinct regions, with C. pipiens prevalent in the north, C. quinquefasciatus in the south, and a hybrid zone in between. The study aimed to determine whether temperature plays a key role in shaping their geographical boundaries and adaptation. To test this,  samples of mosquito larvae from a latitudinal gradient were collected and exposed to high- and low-temperature trials, with survivorship measured for both first and fourth instar larvae. Ben showed that mosquitoes from regions with hotter summers exhibited greater resilience to sustained high temperatures, particularly in the later fourth instar stage, which benefits from advanced development. Survivorship at low temperatures was more variable and challenging to interpret, but some groups demonstrated elevated resilience.

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Figure 4: visual representation of the latitudinal gradients that correspond to Culex pipiens and Culex quinquefasciatus population distributions from Ben’s presentation. Information from Kothers et al. 2009 [5] and Huang et al. 2011 [6].

A key part of this research highlighted differences between above-ground and below-ground C. pipiens populations, which may be significant for understanding local adaptation and survival strategies, as well as disease transmission. Above-ground populations are more exposed to fluctuating temperatures and extreme heat, potentially leading to stronger selection for high-temperature tolerance. In contrast, below-ground populations, such as those in basements or underground storm drains, are insulated from temperature extremes, possibly reducing selective pressure for thermal adaptation. These environmental differences could influence diapause, a physiological state that allows C. pipiens to survive winter, particularly in northern populations with significant seasonal temperature swings.

Ben’s study concluded that selection pressures appear to favor high-temperature tolerance more strongly than low-temperature adaptation, aligning with the ecological relevance of extreme heat events in many regions. The distinction between above-ground and below-ground populations could have implications for understanding local adaptation, mosquito behavior, and the effectiveness of vector control measures. This research not only deepens our understanding of how climate and habitat differences affect mosquito distribution but also provides valuable insights for predicting range shifts and developing targeted vector control strategies under global warming.
 
Ben is passionate about data visualization, with some of his work having gone viral on the subreddit r/dataisbeautiful. Additionally, he has served two years as Treasurer on the UMD Entomology Student Organization (ESO) officer board. To keep up with his work, check out his Google Scholar and/or connect with him on LinkedIn. 

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Ben Burgunder: Overcoming Challenges in Mosquito Identification for West Nile Virus Surveillance  
​The final talk, given by third-year MS student Benjamin Burgunder (he/him) in the Fritz Lab, addressed challenges in tracking West Nile virus (WNv) prevalence in Chicago, IL, focusing on two visually similar [7] mosquito species, Culex restuans and Culex pipiens. Distinguishing between these species requires molecular tools, complicating effective surveillance. The research revisited problem sites identified from Karki et al., 2020, an epidemiological modeling study [8], categorizing them based on whether they had lower, equal, or higher-than-expected numbers of WNv human cases. While species balance (proportion of Cx. restuans to Cx. pipiens) was examined as a potential factor, it did not explain failure to predict infection rates. Ben also measured species-specific WNv prevalence, uncovering that while both species had similar infection rates in the mid-summer, in the late summer, Cx. pipiens infection rates increased while Cx. restuans infection rates declined. Late summer is a time in Chicago when Cx. pipiens is dominant in the landscape and Cx. restuans is nearly absent. This divergence in positivity and abundance may underscore temporal shifts in each species’ role in WNv transmission.

Figure 5: Ben Burgunder (left) and his study organisms (right), both photos provided by Ben Burgunder.

The study concluded that understanding the restuans-to-pipiens balance may be crucial for specific management strategies. This distinction is particularly relevant when considering insecticide resistance, as Cx. pipiens and Cx. restuans may respond differently to chemical controls. By integrating these findings, this research underscores the importance of tailored vector management approaches that account for species behaviors, temporal shifts, and ecological roles to enhance WNv control efforts.
 
Ben is an avid naturalist -- outside of research, you can find him keeping a variety of arthropods (such as tarantulas and isopods) and observing true flies (Order Diptera) at Patuxent Research Refuge in Laurel, MD. His macrophotography was featured on the cover of The Skeeter Virginia Mosquito Control Association's newsletter. If you would like to learn more about his research interests, reach out about any specific photo usage, and/or just want to see some bug photos, check out his website here.
 
These three talks were inspiring not just for their scientific rigor but also for the passion of the presenters. Each speaker demonstrated how their work addresses real-world challenges, from protecting pollinators to managing disease vectors. Whether it is mitigating pesticide impacts on beneficial insects or refining mosquito control strategies in a warming world, this work underscores the importance of applying ecological insights to public health and conservation efforts, bridging science and societal impacts. The challenges we face—climate change, biodiversity loss, and emerging diseases—require innovative solutions informed by science. These graduate students’ research reminds us that the future of public health and ecosystems are deeply intertwined. As we navigate this complex landscape, their work serves as a testament to the power of research to bridge knowledge and application. 

Figure 6: from left to right: Benjamin Burgunder, Michael Adu-Brew, and Benjamin Gregory after presenting their research. The matching outfits for the Bens were unintentional. Photo taken by Megan “Rho” Ma.

References
 
1. International Union for Conservation of Nature (IUCN). (2022, July). Migratory monarch butterfly now endangered - IUCN Red List. Retrieved from [https://iucn.org/press-release/202207/migratory-monarch-butterfly-now-endangered-iucn-red-list](https://iucn.org/press-release/202207/migratory-monarch-butterfly-now-endangered-iucn-red-list).
 
 
2. Wagner, D. L., Grames, E. M., Forister, M. L., Berenbaum, M. R., & Stopak, D. (2021). Insect decline in the Anthropocene: Death by a thousand cuts. Proceedings of the National Academy of Sciences, 118(2). https://doi.org/10.1073/pnas.2023989118.
 
3. U.S. Fish and Wildlife Service. (2024, December). Monarch butterfly proposed for Endangered Species Act protection. Retrieved from [https://www.fws.gov/press-release/2024-12/monarch-butterfly-proposed-endangered-species-act-protection?blm_aid=4129997](https://www.fws.gov/press-release/2024-12/monarch-butterfly-proposed-endangered-species-act-protection?blm_aid=4129997).
 
4. United States Environmental Protection Agency (EPA). (2022). EPA announces Endangered Species Act protection policy for new pesticides. Retrieved from [https://www.epa.gov/newsreleases/epa-announces-endangered-species-act-protection-policy-new-pesticides](https://www.epa.gov/newsreleases/epa-announces-endangered-species-act-protection-policy-new-pesticides).
 
5. Kothera, L., Zimmerman, E. M., Richards, C. M., & Savage, H. M. (2009). Microsatellite characterization of subspecies and their hybrids in Culex pipiens complex (Diptera: Culicidae) mosquitoes along a North-South transect in the central United States. Journal of Medical Entomology, 46(2), 236–248. https://doi.org/10.1603/033.046.0208.
 
6. Huang, S., Molaei, G., & Andreadis, T. G. (2011). Reexamination of Culex pipiens hybridization zone in the eastern United States by ribosomal DNA-based single nucleotide polymorphism markers. The American Journal of Tropical Medicine and Hygiene, 85(3), 434–441. https://doi.org/10.4269/ajtmh.2011.10-0679.
 
7. Harrington, L. C., & Poulson, R. L. (2008). Considerations for accurate identification of adult Culex restuans (Diptera: Culicidae) in field studies. Journal of Medical Entomology, 45(1), 1–8. https://doi.org/10.1093/jmedent/45.1.1.
 
8. Karki, S., Brown, W. M., Uelmen, J., O’Hara Ruiz, M., & Smith, R. L. (2020). The drivers of West Nile virus human illness in the Chicago, Illinois, USA area: Fine-scale dynamic effects of weather, mosquito infection, social, and biological conditions. PLOS ONE, 15(5). https://doi.org/10.1371/journal.pone.0227160.

About the author:
 
M. Rho Ma (they/them) is an incoming Mechanical Engineering PhD student in the Bio-Inspired Advanced Manufacturing (BAM) Laboratory at the James A. Clark School of Engineering at UMD. Their interests in spider functional morphology led them to the Department of Entomology at the Smithsonian National Museum of Natural History (NMNH) and at UMD back in 2022, where they learned about arthropods through taking Entomology graduate courses and teaching the lab section for the undergraduate Biology of Insects (BSCI337) course.