Effects of agrochemical mixtures detected on wildflowers near beef cattle feed yards on Painted Lady Butterflies (Vanessa cardui)

Insect pollinator populations are declining across the United States. Potential causes of observed declines in insect pollinators include, but are not limited to, reduced wildflower availability, monoculture agriculture, parasites, diseases, malnutrition, and pesticides. Pollinators are likely exposed to pesticides used on row crop agriculture and agrochemicals used at livestock production facilities, specifically beef cattle feed yards. To characterize potential pollinator exposure to pesticides and agrochemicals, wildflowers were collected within one kilometer of feed yards and row crop fields. Wildflowers were analyzed for veterinary pharmaceuticals used on feed yards to promote cattle growth, insecticides used to control feed yard pests, and pesticides commonly used in regional row crop agriculture. To further understand potential impacts of pollinator exposure to these unique agrochemical mixtures, a model butterfly species, the painted lady butterfly (Vanessa cardui), was used for toxicity testing. All wildflower samples collected near beef cattle feed yards contained the insecticide moxidectin, which was observed to be extremely toxic to V. cardui larvae (lethal dose in which 50% died (LD50) = 1.7 ± 0.2 ng/g). No other agrochemical identified on wildflowers occurring near feed yards produced any significant effects when V. cardui larvae were exposed within environmentally relevant ranges. Since 82% of wildflowers contained moxidectin plus either a veterinary pharmaceutical or row crop pesticide, a mixture toxicity experiment was conducted. The determined lethal dose in which 15% of larvae died (LD15) of moxidectin was administered with varying concentrations of the other agrochemicals. While no mixture induced any significant effect in this limited trial, we cannot conclude that moxidectin will not potentiate toxicity of other chemicals as has been reported in the literature. This preliminary study has identified the presence of previously unknown agrochemical mixtures emanating from feed yards and row crops in the Southern High Plains (SHP) on wildflowers and underscored the potential for adverse effects on pollinating insects.