Insecticide application prevents honey bees from realizing benefits of native forage in an agricultural landscape

Health and population status of bees is negatively affected by anthropogenic stressors, many of which co-occur in agricultural settings. While pollinator habitat (often involving plantings of native forbs) holds promise to benefit both managed and wild bees, important issues remain unresolved. These include whether conventional, broad-spectrum insecticide use negates these benefits and how non-native, managed honey bees affect wild bees in these areas. We conducted a three-year replicated study in a Midwestern corn and soybean production region (i.e., Iowa, USA). We assessed acute and delayed effects of commercial-scale spraying of a commonly used, foliar-applied insecticide (λ-cyhalothrin) in soybean on the productivity of honey bee colonies kept within these fields. Colony health metrics showed no immediate significant differences between insecticide treated and untreated crop fields. As expected, health metrics declined in all colonies after soybean ceased flowering. Interestingly, the subset of colonies from untreated fields given access to restored prairies rebounded. However, colonies from insecticide-treated fields showed reduced growth, queen egg-laying, and survival, even when given access to prairies. In addition, we did not observe a detectable impact of honey bee apiaries on wild bee abundance or diversity at these prairies over a three-year period. Our findings underscore the complex interactions between agricultural practices and bee health, highlighting the necessity of integrated pest management and the conservation of native floral resources to support pollinator populations and sustainable beekeeping in agroecosystems.