Abstract
Establishment and maintenance of milkweed plants (Asclepias spp.) in agricultural landscapes of the north central United States are needed to reverse the decline of North America's eastern monarch butterfly (Danaus plexippus) population. Because of a lack of toxicity data, it is unclear how insecticide use may reduce monarch productivity when milkweed habitat is placed near maize and soybean fields. To assess the potential effects of foliar insecticides, acute cuticular and dietary toxicity of 5 representative active ingredients were determined: beta-cyfluthrin (pyrethroid), chlorantraniliprole (anthranilic diamide), chlorpyrifos (organophosphate), and imidacloprid and thiamethoxam (neonicotinoids). Cuticular median lethal dose values for first instars ranged from 9.2 x 10-3 to 79 μg/g larvae for beta-cyfluthrin and chlorpyrifos, respectively. Dietary median lethal concentration values for second instars ranged from 8.3 x 10-3 to 8.4 μg/g milkweed leaf for chlorantraniliprole and chlorpyrifos, respectively. To estimate larval mortality rates downwind from treated fields, modeled insecticide exposures to larvae and milkweed leaves were compared to dose-response curves obtained from bioassays with first-, second-, third-, and fifth-instar larvae. For aerial applications to manage soybean aphids, mortality rates at 60 m downwind were highest for beta-cyfluthrin and chlorantraniliprole following cuticular and dietary exposure, respectively, and lowest for thiamethoxam. To estimate landscape-scale risks, field-scale mortality rates must be considered in the context of spatial and temporal patterns of insecticide use.
Recommended Citation
N. Krishnan et al., "Assessing Field-Scale Risks of Foliar Insecticide Applications to Monarch Butterfly (Danaus Plexippus) Larvae," Environmental Toxicology and Chemistry, vol. 39, no. 4, pp. 923 - 941, Wiley Periodicals, Apr 2020.
The definitive version is available at https://doi.org/10.1002/etc.4672
Department(s)
Biological Sciences
Keywords and Phrases
Conservation; Insecticides; Monarch butterfly; Risk assessment; Toxicology
International Standard Serial Number (ISSN)
0730-7268; 1552-8618
Document Type
Article - Journal
Document Version
Final Version
File Type
text
Language(s)
English
Publication Date
01 Apr 2020
PubMed ID
31965612
Comments
The present study was supported by the Agriculture and Food Research Initiative Pollinator Health Program (grant 20186701327541) from the US Department of Agriculture's National Institute of Food and Agriculture; the College of Agriculture and Life Sciences, Iowa State University (ISU); and the Iowa Monarch Conservation Consortium.