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.
Research Projects (Ongoing)
1. Assessing toxicity and risk of newer conventional insecticides and biological fungicides on monarch butterfly larvae: Studies are being undertaken with four insecticides (cyantraniliprole, sulfoxaflor, afidopyropen, and broflanilide) and two fungicides (Double Nickel® and Howler®). Also, the compatibility of select tank mixes and their mixture effects are being assessed. This work is being undertaken by Michael Adu-Brew and Sabrina Purtee.
2. Developing rearing methods and generating lifecycle data for a surrogate butterfly species: Studies are being undertaken with eastern-tailed blue butterflies, as a potential surrogate for listed (endangered/threatened) lycaenid species. Following successful protocol development and data generation, toxicity bioassays would be undertaken. This work is currently being undertaken by Margaret Kato and Daffa Villandiar.
3. Measuring diamide seed treatment runoff concentrations: Studies are being undertaken at UMD's Beltsville's Facility. Chlorantraniliprole concentrations are being measured in milkweed leaves, surrounding soil, and select corn plants. This work is being undertaken by Michael Adu-Brew, Jillian Stewart, Michael Zhao, and Sabrina Purtee.
4. Sampling insects in diamide-treated and untreated plots/plants: Studies are being undertaken at UMD's Beltsville and Campus Greenhouse Facilities. In the field, insects are sampled on diamide-exposed and control plots through plant observations, pitfall traps, bee bowls, and sticky traps. In the greenhouse, monarch butterfly fitness and movement are being assessed in cages containing diamide-treated and untreated milkweed. This work is being undertaken by Jillian Stewart and Luke Humke.
5. Determining the mechanism leading to arrested pupal and adult ecdysis: Studies are being undertaken on corn earworms, fall armyworms, Colorado potato 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 undertaken by Sabrina Purtee and Jillian Stewart.
6. Generating species sensitivity distribution (SSD) models for Coleoptera and Lepidoptera: Using Google Scholar and ECOTOX databases, coleopteran and lepidopteran toxicity bioassays are being screened and SSDs are being generated where possible. Thereafter, foliar insecticide risk is being assessed for listed species in these families. This work is being undertaken by Margaret Kato and Niranjana Krishnan.
Publications
2022
Grant TJ*, Fisher KE*, Krishnan N*, Mullin AN, Hellmich RL, Sappington TW, Adelman JS, Coats JR, Hartzler RG, Pleasants JM, Bradbury SP. 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.
2021
Hall MJ*, Krishnan N*, Coats JR, Bradbury SPP. 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. 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. 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. 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. Monarch butterfly (Danaus plexippus) life stage risks from foliar and seed treatment insecticides. Environmental Toxicology and Chemistry. 10.1002/etc.5016
2020
Krishnan N, Yang Z, Bidne KG, Hellmich RL, Coats JR, Bradbury SP. Assessing field-scale risks of foliar insecticide applications to monarch butterfly (Danaus plexippus) larvae. Environmental Toxicology and Chemistry. 10.1002/etc.4672
2019
Krishnan N. Aquatic Toxicity Tests. Perspectives of Aquatic Toxicology Wikibook. Jovanovic B, ed. https://en.wikibooks.org/wiki/Perspectives_of_Aquatic_Toxicology
Grant TJ*, Fisher KE*, Krishnan N*, Mullin AN, Hellmich RL, Sappington TW, Adelman JS, Coats JR, Hartzler RG, Pleasants JM, Bradbury SP. 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.
2021
Hall MJ*, Krishnan N*, Coats JR, Bradbury SPP. 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. 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. 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. 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. Monarch butterfly (Danaus plexippus) life stage risks from foliar and seed treatment insecticides. Environmental Toxicology and Chemistry. 10.1002/etc.5016
2020
Krishnan N, Yang Z, Bidne KG, Hellmich RL, Coats JR, Bradbury SP. Assessing field-scale risks of foliar insecticide applications to monarch butterfly (Danaus plexippus) larvae. Environmental Toxicology and Chemistry. 10.1002/etc.4672
2019
Krishnan N. Aquatic Toxicity Tests. Perspectives of Aquatic Toxicology Wikibook. Jovanovic B, ed. https://en.wikibooks.org/wiki/Perspectives_of_Aquatic_Toxicology