Neonicotinoid insecticidal seed-treatment on corn contaminates interseeded cover crops intended as habitat for beneficial insects
Neonicotinoid seed treatments are extensively used to systemically protect corn from invertebrate herbivory. Interseeding cover crops can promote beneficial insect communities and their ecosystem services such as predation on pests, and this practice is gaining interest from farmers. In this study, cereal rye (Secale cereale) and hairy vetch (Vicia villosa) were planted between rows of early vegetative corn that had been seed-treated with thiamethoxam. Thiamethoxam and its insecticidal metabolite, clothianidin were quantified in cover crop leaves throughout the growing season. Thiamethoxam was present in cereal rye at concentrations ranging from 0 to 0.33 ± 0.09 ng/g of leaf tissue and was detected on six out of seven collection dates. Cereal rye leaves contained clothianidin at concentrations from 1.05 ± 0.22 to 2.61 ± 0.24 ng/g and was present on all sampling dates. Both thiamethoxam and clothianidin were detected in hairy vetch on all sampling dates at rates ranging from 0.10 ± 0.05 to 0.51 ± 0.11 ng/g and 0.56 ± 0.15 to 9.73 ± 5.04 ng/g of leaf tissue, respectively. Clothianidin was measured at a higher concentration than its precursor, thiamethoxam, in both plant species on every sampling date. Neonicotinoids entering interseeded cover crops from adjacent treated plants is a newly discovered route of exposure and potential hazard for non-target beneficial invertebrates. Future research efforts should examine the effects of systemic insecticides on biological communities in agroecosystems whose goal is to diversify plant communities using methods such as cover cropping.
KeywordsClothianidin Insecticide Thiamethoxam Non-targets Risk assessment Zea mays
We thank Kassidy Weathers, Nicole Schultz, Cedric Gentils, Liz Adee, Tommy Fenster and Alex Nikolaus for their assistance in plant tissue collection and sample processing. Mark Longfellow assisted with ELISA development.
This research was supported by general funds from Ecdysis Foundation, and grant support from Threshold Foundation, Globetrotter Foundation, and by support from farmers, ranchers, and beekeepers around the world.
Compliance with ethical standards
Conflict of interest
MMB is employed by Ecdysis Foundation and South Dakota State University. JGL was formerly employed by USDA and is the Director for Ecdysis Foundation and CEO for Blue Dasher Farm. We have not received any research support or financial contributions from companies mentioned in this manuscript.
This article does not contain any studies with animals performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
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