Our lab is employing the adverse outcome pathway (AOP) framework to estimate the risk of pesticide exposures to insects at different levels of biological organization. This is being undertaken via three research themes that incorporate in vitro, in vivo, and in silico methods:
AOP development from molecular initiating events to organismal effects
AOP development from organismal to population level effects
AOP employment to inform interspecies extrapolation
AOP development from molecular initiating events to organismal effects: Novel modes of action
We are elucidating unique low-dose effects produced by certain pesticides and other neuroactive chemicals on insect development, specifically insect pupal and adult ecdysis. These effects strongly suggest that the neuroactive compounds act through a novel mode of action. Results obtained from this project will broaden understanding of insect ecdysis and the interplay between neuroendocrine hormones and neurotransmitters. It could also lead to the development of more sustainable and targeted pest management strategies.
AOP development from organismal to population level effects: Non-target testing
We are assessing the toxicity and risk of chemical and biological pesticides on non-target insects, including insect species of conservation concern. This involves developing conceptual models to evaluate potential exposure pathways, undertaking toxicity bioassays, estimating exposure, and analyzing field and landscape-scale effects. Results obtained from this project will help determine the susceptibility of non-target insects to different pesticide use scenarios and could inform conservation practices for declining species.
AOP employment to inform interspecies extrapolation: Interspecies differences
We are elucidating differences in pesticide susceptibility within and across insect orders. This involves determining toxicokinetic and toxicodynamic factors responsible for differing susceptibilities, identifying surrogate species for toxicity testing, and extrapolating effects across species and orders. Results obtained from this project can help estimate pesticide toxicity for hard-to-rear and endangered/threatened species, and could reduce, refine, and replace insect use in toxicity bioassays.
Cover photo taken by Mark Sherwood from College of Computer, Mathematical, and Natural Sciences, University of Maryland, College Park
Research Projects (Ongoing)
1. Assessing toxicity and risk of newer conventional insecticides and biological fungicides on monarch butterfly and eastern-tailed blue butterflies: Studies are being undertaken with five insecticides (cyantraniliprole, chlorantraniliprole, sulfoxaflor, afidopyropen, and broflanilide) and two fungicides (Double Nickel® and Howler®) in the lab and greenhouse. Also, the compatibility of select tank mixes and their mixture effects are being assessed. This work is being primarily undertaken by Michael Adu-Brew, Jillian Stewart, and Sabrina Purtee.
2. Measuring diamide seed treatment runoff concentrations: Studies were undertaken at UMD's Beltsville's Facility. Chlorantraniliprole and neonicotinoid concentrations are being measured in milkweed leaves, surrounding soil, and select corn plants. This work is being primarily undertaken by Michael Adu-Brew, Michael Zhao, Teagan Flaherty, and Nico Brown.
3. Sampling insects in diamide-treated and untreated plots: Studies were undertaken at UMD's Beltsville Facility. Insects are sampled on diamide-exposed and control plots through plant observations, pitfall traps, bee bowls, and sticky traps. This work is being primarily undertaken by Jillian Stewart and Luke Humke.
4. Determining the mechanism leading to arrested pupal and adult ecdysis: Studies are being undertaken on corn earworms, fall armyworms, Colorado potato beetles, red flour beetles, and fruit flies exposed to sublethal doses of nicotinic acetylcholine receptor agonists and GABA receptor antagonists. Specifically, the effects of these compounds on ecdysis and crustacean cardioactive peptide (CCAP) neurons are being assessed. This work is being primarily undertaken by Sabrina Purtee, Teagan Flaherty, and Nico Brown.
5. Assessing alterations in lipid metabolism: We are determining how de-novo lipogenesis varies in migratory vs. non-migratory monarchs and in indoor vs. outdoor reared monarchs. We are then assessing the effect of pesticides that disrupt mitochondrial function and correspondingly, de-novo lipogenesis. This work is being primarily undertaken by Luke Humke and Ceri Gameson.
Research Projects (Completed)
1. Developing rearing methods and generating lifecycle data for a surrogate butterfly species: Rearing methods and lifecycle data were generated for eastern-tailed blue butterflies, a potential surrogate for listed (endangered/threatened) lycaenid species in pesticide toxicity bioassays. This work was primarily undertaken by Luke Humke and Margaret Kato. A paper describing this work has been accepted.
2. Generating species sensitivity distribution (SSD) models for Coleoptera: Using Google Scholar and ECOTOX databases, coleopteran toxicity bioassays were screened and SSDs are being generated. Thereafter, insecticide risk was assessed for listed and non-target coleopteran species and assessments were compared with honeybees. This work was undertaken by Margaret Kato. A manuscript describing this work is currently close to submission.
Relevant Research Publications
Krishnan N, Gorman C, Stewart J, Bradbury SP, Jurenka RA. 2025. Using insecticidal compounds to elucidate the potential role of neurotransmitters in Lepidoptera pupal ecdysis. Scientific Reports. https://doi.org/10.1038/s41598-025-88623-y
Grant TJ*, Fisher KE*, Krishnan N*, Mullin AN, Hellmich RL, Sappington TW, Adelman JS, Coats JR, Hartzler RG, Pleasants JM, Bradbury SP. 2022. Monarch butterfly ecology, behavior, and vulnerabilities in north central USA agricultural landscapes: Transdisciplinary research to support conservation decisions. BioScience. 10.1093/biosci/biac094
*Authors contributed equally.
Hall MJ*, Krishnan N*, Coats JR, Bradbury SP. 2021. Estimating screening-level risks of insecticide exposure to lepidopteran species of conservation concern in agroecosystems. American Chemical Society Symposium Series. 10.1021/bk-2021-1390.ch008
*Authors contributed equally.
Krishnan N, Jurenka RA, Bradbury SP. 2021. Neonicotinoids can cause arrested pupal ecdysis in Lepidoptera. Scientific Reports. 10.1038/s41598-021-95284-0
Krishnan N*, Hall MJ*, Hellmich RL, Coats JR, Bradbury SP. 2021. Assessing the toxicity of varroa-active dsRNA on monarch butterfly (Danaus plexippus) larvae. PLOS ONE. 10.1371/journal.pone.0251884
*Authors contributed equally.
Grant TJ, Krishnan N, Bradbury SP. 2021. Conservation risks and benefits of establishing monarch butterfly (Danaus plexippus) breeding habitat in close proximity to maize and soybean fields in the U.S. Midwest: A landscape-scale analysis of foliar insecticide effect on non-migratory monarch butterfly populations. Integrated Environmental Assessment and Management. 10.1002/ieam.4402
Krishnan N, Yang Z, Aust M, Hellmich RL, Coats JR, Bradbury SP. 2021. Monarch butterfly (Danaus plexippus) life stage risks from foliar and seed treatment insecticides. Environmental Toxicology and Chemistry. 10.1002/etc.5016
Krishnan N, Yang Z, Bidne KG, Hellmich RL, Coats JR, Bradbury SP. 2020. Assessing field-scale risks of foliar insecticide applications to monarch butterfly (Danaus plexippus) larvae. Environmental Toxicology and Chemistry. 10.1002/etc.4672
*Authors contributed equally.
Hall MJ*, Krishnan N*, Coats JR, Bradbury SP. 2021. Estimating screening-level risks of insecticide exposure to lepidopteran species of conservation concern in agroecosystems. American Chemical Society Symposium Series. 10.1021/bk-2021-1390.ch008
*Authors contributed equally.
Krishnan N, Jurenka RA, Bradbury SP. 2021. Neonicotinoids can cause arrested pupal ecdysis in Lepidoptera. Scientific Reports. 10.1038/s41598-021-95284-0
Krishnan N*, Hall MJ*, Hellmich RL, Coats JR, Bradbury SP. 2021. Assessing the toxicity of varroa-active dsRNA on monarch butterfly (Danaus plexippus) larvae. PLOS ONE. 10.1371/journal.pone.0251884
*Authors contributed equally.
Grant TJ, Krishnan N, Bradbury SP. 2021. Conservation risks and benefits of establishing monarch butterfly (Danaus plexippus) breeding habitat in close proximity to maize and soybean fields in the U.S. Midwest: A landscape-scale analysis of foliar insecticide effect on non-migratory monarch butterfly populations. Integrated Environmental Assessment and Management. 10.1002/ieam.4402
Krishnan N, Yang Z, Aust M, Hellmich RL, Coats JR, Bradbury SP. 2021. Monarch butterfly (Danaus plexippus) life stage risks from foliar and seed treatment insecticides. Environmental Toxicology and Chemistry. 10.1002/etc.5016
Krishnan N, Yang Z, Bidne KG, Hellmich RL, Coats JR, Bradbury SP. 2020. Assessing field-scale risks of foliar insecticide applications to monarch butterfly (Danaus plexippus) larvae. Environmental Toxicology and Chemistry. 10.1002/etc.4672