Effects of insecticide spray drift on arthropod prey resources of birds in grasslands in Minnesota

Authors: GOEBEL, KATELIN - University Of Minnesota; ANDERSON, DAVID - Us Geological Survey (USGS); Rice, Pamela; DAVROS, NICOLE - Minnesota Department Of Natural Resources

Submitted to: Journal of Wildlife Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2024
Publication Date: 3/10/2024
Citation: Goebel, K.M., Anderson, D.E., Rice, P.J., Davros, N.M. 2024. Effects of insecticide spray drift on arthropod prey resources of birds in grasslands in Minnesota. Journal of Wildlife Management. 88(4). Article e22572. https://doi.org/10.1002/jwmg.22572.
DOI: https://doi.org/10.1002/jwmg.22572

Interpretive Summary: Insecticides are sprayed on soybeans in the farmland region of the Upper Midwest USA to combat soybean aphids. A concern is insecticides may drift beyond targeted soybean fields into nearby grassland cover where birds and other animals that eat arthropods (e.g., insects and spiders) search for food. Arthropods are important to grassland ecology and their exposure to insecticides may result in injury or death, which may negatively impact grassland animals that rely on arthropods as a food source. The objective of our research was to measure effects of soybean aphid insecticides on arthropods in grasslands, especially those that are important in grassland bird diets. We compared arthropod abundance and biomass in grasslands adjacent to soybean fields sprayed with insecticides to that of grasslands adjacent to agricultural fields without spray. Total arthropod abundance (3–5 days after spraying), bird prey abundance (19–21 days after spraying), and Coleopteran family (e.g., beetles) richness (3–5 days after spraying) were lower in grasslands near the sprayed fields. Our results reveal that reductions in arthropod food abundance for grassland birds are associated with insecticide spraying, up to 21 days after the spraying event (the duration of our sampling). We also suggest potential strategies to reduce these effects. This information is important to farmers, wildlife managers and scientists with the shared goal of sustainable agriculture and environmental quality.

Technical Abstract: Soybean aphid (Aphis glycines) insecticides are used throughout the farmland region of Minnesota and the Upper Midwest USA to combat insect pests. However, these broad-spectrum, foliar spray insecticides have the potential to drift beyond target fields into nearby grassland cover where birds and other insectivores forage. Arthropods serve important roles in grassland ecology and are susceptible to mortality and sublethal effects from exposure to these insecticides. Our objective was to assess effects of soybean aphid insecticides on arthropods in grasslands, especially those that are important in grassland bird diets. We measured the abundance, consumable biomass, and family richness of insects and spiders in grasslands adjacent to soybean fields in an agricultural landscape that were treated with chlorpyrifos, lambda-cyhalothrin, and bifenthrin; the 3 most common insecticides used to treat soybean aphids in Minnesota. We compared measures at these focal sites to samples collected at reference sites adjacent to corn fields not sprayed for aphids during 3 periods: 1–3 days before spraying, 3–5 days post-spraying, and 19–21 days post-spraying. We detected short-term reductions (3-5 days or 19-21 days) in total arthropod abundance, bird prey abundance, and Coleopteran family richness in focal grasslands bordered by fields sprayed with foliar insecticides. The total abundance of arthropods in focal grasslands was lower 3–5 days after insecticide applications (ß = -49.06, 95% CI = -89.84 – -8.28). The abundance of arthropods important in grassland bird diets (specifically, Araneae, Coleoptera, Orthoptera, and Lepidoptera larvae) was also lower after nearby spraying, with lower abundance measured in focal sites 19–21 days post-spraying (ß = -23.94, 95% CI = -44.99 – -2.88). Coleoptera family richness at focal sites was lower than at reference sites 3–5 days after insecticide applications (ß = -0.94, 95% CI = -1.82 – -0.06). Measures of total consumable dry biomass, bird prey biomass, family richness of Araneae, family richness of Hemiptera, and family richness of Orthoptera were not different between focal and reference sites post-spraying. Our results reveal that reductions in arthropod food abundance for grassland birds are associated with insecticide spraying up to 21 days (the duration of our sampling) after the spraying event, and we suggest potential strategies to mitigate these effects.