Mitigating Risk of Butterfly Habitat Contamination by Pesticides on Agricultural Land

Butterfly declines have been documented with long-term data sets in Europe and in the US. Analyses have shown that habitat loss and pesticide use are major drivers of the declines. Agricultural field margins have been suggested as opportune locations for habitat installation, but their use coincides with risk of pesticide contamination of host plants. Neonicotinoids have become the pesticide of choice for various crops like corn and soy, but are especially concerning for butterflies because of their systemic mode of action. There isn’t enough research on habitat contamination in working landscapes or toxicity of neonicotinoids to butterflies to determine if installing habitat in agriculture is beneficial for butterfly abundance and diversity. To learn more, we conducted a field experiment to measure concentrations of Thiamethoxam (TMX) taken up by butterfly host plants (such as milkweed and sunflowers) downslope of plots planted with pesticide-coated corn seeds. We also carried out a lab experiment to measure toxicity of Thiamethoxam to painted lady butterfly larvae in order to interpret the risk of TMX concentrations found in sunflowers. The highest concentration of TMX found in the field was about 40 ppb, which was lower than the concentration at which we found significant sublethal and lethal effects in the lab, between 25,000 ppb and 30,000 ppb. We also tested if buffer strips and cover crops could reduce the concentration taken up by butterfly host plants. Neither treatment had a significant effect on concentration. More research needs to be completed to fill this gap in knowledge, and to create habitat that has positive conservation value.