Small-Grain Cover Crops Have Limited Effect on Neonicotinoid Contamination from Seed Coatings

Abstract

Neonicotinoids from insecticidal seed coatings can contaminate soil in treated fields and adjacent areas, posing a potential risk to nontarget organisms and ecological function. To determine if cover crops can mitigate neonicotinoid contamination in treated and adjacent areas, we measured neonicotinoid concentrations for three years in no-till corn-soybean rotations, planted with or without neonicotinoid seed coatings, and with or without small grain cover crops. Although neonicotinoids were detected in cover crops, high early season dissipation provided little opportunity for winter-planted cover crops to absorb significant neonicotinoid residues; small grain cover crops failed to mitigated neonicotinoid contamination in either treated or untreated plots. As the majority of neonicotinoids from seed coatings dissipated shortly after planting, residues did not accumulate in soil, but persisted at concentrations below 5 ppb. Persistent residues could be attributed to historic neonicotinoid use and recent, nearby neonicotinoid use. Tracking neonicotinoid concentrations over time revealed a large amount of local interplot movement of neonicotinoids; in untreated plots, contamination was higher when plots were less isolated from treated plots.

Toxicity of clothianidin to common Eastern North American fireflies

“…pyralis . Although residual neonicotinoid concentrations in soil are often below 100 ng g −1 ( Schaafsma et al, 2016 ; Radolinski et al, 2019 ; Pearsons et al, 2021 ), concentrations can regularly exceed these levels after agricultural applications (as high as 594 ng g −1 23 days after planting neonicotinoid-coated seeds; ( Radolinski et al, 2019 )), after turf applications (3 × higher than in agronomic settings; ( Armbrust & Peeler, 2002 )) and after soil drenches to manage hemlock wooly adelgid (over 4,000 ng AI g −1 soil; Knoepp et al, 2012 ). Such high concentrations are well within the acutely toxic and chronically lethal range for Pt.…”

“…To the soil in each assay container, we added 0.5 mL of the appropriate clothianidin stock solution, allowed the acetone to completely evaporate, then added two mL of DI water to moisten the soil and to achieve clothianidin concentrations of 0 ng g −1 , 10 1 ng g −1 soil, 10 2 ng g −1 soil, 10 3 ng g −1 soil , 10 4 ng g −1 soil. We chose this concentration range (10 1 –10 4 ng g −1 soil) to encompass the range of neonicotinoid concentrations in soil that have been measured in potential firefly habitats ( Knoepp et al, 2012 ; Schaafsma et al, 2015 ; Pearsons et al, 2021 ).…”

“…These larvae inhabit forested, suburban, and agricultural soils, where neonicotinoid insecticides are often applied directly, or via coatings on crop seeds, to protect against pests ( Knoepp et al, 2012 ; Douglas & Tooker, 2015 ; Simon-Delso et al, 2015 ). In these habitats, neonicotinoid concentrations in soil can range from less than 5 ng g −1 to over 4,000 ng g −1 ( Knoepp et al, 2012 ; Schaafsma et al, 2015 ; Pearsons et al, 2021 ), concentrations that could plausibly influence behavior and survival of firefly larvae ( Lee et al, 2008 ). Some indirect evidence suggests that firefly larvae are susceptible to neonicotinoids because adult lampyrid densities have been found to be lower where neonicotinoid-coated seeds were planted ( Disque et al, 2019 ); however, to our knowledge, there have been no direct evaluations of how terrestrial firefly larvae respond to neonicotinoid-treated soil.…”

Honeydew as a newly described route of insecticide exposure to beneficial insects

“…Before systemic insecticides degrade, they can be transported to adjacent crops, cooccurring weeds, field side vegetation, or adjacent habitats or ecosystems by movement in water or insecticide drift (Goulson, 2013;Greatti et al, 2006;Hladik et al, 2014;Krupke et al, 2012;Pearsons et al, 2021;Tsvetkov et al, 2017) (Figure 2d, e, f). During these movements, systemic insecticides can reach non-target plants, even at concentrations exceeding those of the treated crop (Botías et al, 2015).…”

“…Water-soluble systemic insecticides are transported from agricultural lands to adjacent habitats or ecosystems by movement in water or by insecticide drift (Greatti et al, 2006;Krupke et al, 2012;Pearsons et al, 2021;Tsvetkov et al, 2017). For instance, a study detected imidacloprid in 90% of the water samples collected from agricultural regions of California (Starner and Goh, 2012).…”