Dr. Maggie Douglas, an assistant professor from Dickinson College, managed to stump most of a room full of entomologists when she asked them if pesticide use in United States agriculture was going up or down over time. There were a few embarrassed laughs, but Douglas reassured everyone; “It’s a complicated question. There’s disagreement in the scientific community.”
But, back to the question of whether insecticide use is increasing or decreasing. According to Douglas, it’s hard to tell because insecticide use can be measured in different ways: you can look at the percentage of land treated, the weight of insecticide products applied, or the potency of the insecticides. Douglas collected data from government sources and standardized the data using potency in terms of the dose needed to kill a honey bee. While the overall weight of insecticides has declined over the past 20 years, making it seem that pesticide use is decreasing, the number of lethal doses has risen dramatically. This change has largely come from regions of the United States that grow corn and soybeans, and by integrating data from additional sources, Douglas showed that the increase is being driven by neonicotinoid seed treatments (Figure 1).
Neonicotinoids, known as neonics, are a type of insecticide that is relatively safe for mammals but acutely toxic to insects. They are applied to crops as seed treatments, where the seedling takes up the insecticidal compounds through its roots and circulates them as it grows. Douglas showed that nearly all corn grown in the U.S. is treated with neonic seed treatments, and that the amount per seed is increasing.
In her current lab, Douglas continues to work on this important topic. She integrates data from the USDA, USGS, and EPA to create detailed maps showing the number of toxic doses (the same measurements she used to understand if pesticide use was increasing or decreasing) over time and location. She’s collaborating with other researchers to use these maps to understand insecticide impacts on beneficials such as pollinators. Douglas’ research serves an important role: she looks at broad trends in pesticide-use, gathering data from diverse sources, and asking tricky questions. She left everyone in the room with a less tangled story of pesticide use patterns in the U.S., but at the same time suggested yet another question to explore: As we research the impacts of pesticides on insects, how do we integrate farmer decision-making and account for the lack of transparency surrounding chemicals used in seed treatments?
Douglas MR, Sponsler DB, Lonsdorf E V., Grozinger CM, 2019. Rising insecticide potency outweighs falling application rate to make US farmland increasingly hazardous to insects. bioRxiv 715763.
Douglas MR, Tooker JF, 2016. Meta-analysis reveals that seed-applied neonicotinoids and pyrethroids have similar negative effects on abundance of arthropod natural enemies. PeerJ 1–26.
Douglas MR, Rohr JR, Tooker JF, 2015. Neonicotinoid insecticide travels through a soil food chain, disrupting biological control of non-target pests and decreasing soya bean yield. J. Appl. Ecol. 52, 250–260.
Douglas MR, Tooker JF, 2015. Large-scale deployment of seed treatments has driven rapid increase in use of neonicotinoid insecticides and preemptive pest management in U.S. Field crops. Environ. Sci. Technol. 49, 5088–5097.
Maria Cramer is a PhD student in the Hamby Lab studying non-target effects of pyrethroid insecticides and RNAi in field corn.
Veronica Yurchak is a PhD student in the Hooks Lab studying the potential benefits of interplanted living mulches for weed suppression, insect natural enemy enhancement and pollinator conservation in vegetable systems.