The non-target impacts of neonicotinoid seed treatments on beneficial insects in sunflower fields

The use of neonicotinoid insecticides as seed-dressings has become nearly ubiquitous within conventional row-crop agriculture. The extensive use of such products have conservationists and researchers concerned for the health of non-targeted organisms which might be exposed to the insecticide through a number of pathways. In this two year study, both insecticide treated (Cruiser®, rate: .25 mg a.i. (thiamethoxam)/seed) and untreated sunflower (Helianthus annuus [Family: Asteraceae]) fields were planted in main sunflower production areas of Eastern and Central South Dakota. Soil and foliar arthropod communities, as well as leaf-tissue insecticide content were examined regularly throughout the growing season to compare the two treatments. Seed-treated fields had significantly fewer natural enemies than the untreated fields, but herbivore populations did not differ between treatments. Thiamethoxam and Clothianidin (a toxic metabolite of thiamethoxam) were found at high levels in sunflower leaf tissue early in the growing season (through V6) but levels quickly fell and remained relatively low for the remainder of the plants growth. Yields were unaffected by insecticidal seed treatments. The results demonstrated that neonicotinoid seed-treatments have little effect on herbivore populations within sunflower fields, but do negatively impact beneficial insect communities. Beneficial insects may come into contact with the insecticide through facultative herbivory, by feeding on toxic nectar, or perhaps tri-trophically by consuming insecticide-laden prey. In the future, the risks of using insecticidal seed-treatments must be weighed against any benefits.