Milkweed in agricultural field margins - A neonicotinoid exposure route for pollinators at multiple life stages
Naujokaitis-Lewis I, Endicott S, Gaudreault E and others. The Science of the total environment, August 2024.
Go to the paper May need a subscription · doi:10.1016/j.scitotenv.2024.175622
What this paper is about
Neonicotinoid seed treatments do not stay in the crop. Milkweed was sampled from 95 field margins next to treated fields in 2017 and 2018, and tested across several tissue types rather than just leaves.
That matters because monarchs meet the plant at every stage: eggs on it, caterpillars eating leaves, adults drinking from the flowers. Each tissue is a separate exposure route.
Summarised here from the abstract below. Not the authors’ words.
Abstract
Neonicotinoid insecticides move from targeted crops to wildflowers located in adjacent field margins, acting as a potential exposure source for wild pollinators and insect species of conservation concern, including monarch butterflies. Monarchs rely on milkweed over multiple life stages, including as a host plant for eggs and a food source for both larvae (leaves) and adults (flowers). Milkweeds, which are closely associated with field margins, can contain neonicotinoid residues, but previous assessments are constrained to a single plant tissue type. In 2017 and 2018, we sampled milkweeds from 95 field margins adjacent to crop fields (corn, soybean, hay, wheat, and barley) in agricultural landscapes of eastern Ontario, Canada. Milkweeds were sampled during the flower blooming period and leaves and flower tissues were analysed. The neonicotinoids acetamiprid, clothianidin, thiamethoxam, and thiacloprid were detected. Maximum concentrations in leaf samples included 10.30 ng/g of clothianidin in 2017, and 24.4 ng/g of thiamethoxam in 2018. Clothianidin and thiamethoxam percent detections in flowers (72 % and 61 %, respectively) were significantly higher than detections in leaves (24 % and 31 %, respectively). Thiamethoxam concentrations were significantly higher in paired flower samples than leaf samples (median 0.33 ng/g vs <0.07 ng/g) while clothianidin concentrations also trended higher in flowers (median 0.18-0.55 ng/g vs <0.18 ng/g). Only thiamethoxam showed significant differences between years, and we found no effect of crop type, with hay, soybean and corn fields all yielding 50-56 % detections in leaves. We found significantly higher concentrations in older milkweed flowers than young flowers or leaves (medians 0.87 ng/g vs <0.18 ng/g and 0.45 ng/g vs <0.07 ng/g for clothianidin and thiamethoxam, respectively). Our results highlight the importance of considering variation in milkweed tissue type and age of flowers in neonicotinoid exposure risk assessments. Efforts to increase milkweed availability in agricultural landscapes should consider how exposure to neonicotinoids can be mitigated.
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Milkweed USA. (2026). Milkweed in agricultural field margins - A neonicotinoid exposure route for pollinators at multiple life stages (listing). Retrieved DATE, from https://milkweedusa.com/research/milkweed-in-agricultural-field-margins-a-neonicotinoid-exposure-route-2024/
"Milkweed in agricultural field margins - A neonicotinoid exposure route for pollinators at multiple life stages (listing)." Milkweed USA, 2026, https://milkweedusa.com/research/milkweed-in-agricultural-field-margins-a-neonicotinoid-exposure-route-2024/. Accessed DATE.
Milkweed USA. "Milkweed in agricultural field margins - A neonicotinoid exposure route for pollinators at multiple life stages (listing)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/research/milkweed-in-agricultural-field-margins-a-neonicotinoid-exposure-route-2024/.
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title = {Milkweed in agricultural field margins - A neonicotinoid exposure route for pollinators at multiple life stages (listing)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/research/milkweed-in-agricultural-field-margins-a-neonicotinoid-exposure-route-2024/},
note = {Accessed DATE}
}