Evaluation of herbicide formulations and spreading agents on survival of the bumblebee Bombus impatiens following spray and contact exposure

Surfactants are often included as co-formulants in the application of herbicides to aid in spreading and adherence to plant surfaces, but toxicity to native bees has not been extensively tested. In a set of progressive experiments, we evaluated effects of products containing glyphosate and spreading agents, as well as spreading agents alone, on bumblebees (Bombus impatiens Cresson) using parametric survival analysis. We test spreaders from multiple chemical classes including Silwet L-77© (trisiloxane), Alligare 90© (polyoxyethylene), and Southern Ag SA-50© (C10-16 alcohols). We report low lethality of high-glyphosate herbicide formulations (Rodeo©), but bee mortality increased ~20% with addition of a silicone-based spreading agent (Silwet L-77©). Spreaders alone strongly affected bee survival: effects were concentration-specific and did not differ depending on exposure method (spray application vs. application to surfaces contacted by bees). The widely used trisiloxane-based spreader Silwet L-77© was especially hazardous, and exposure to high concentrations of Silwet L-77© caused rapid and near-total mortality in B. impatiens. Analysis of whole-bee cuticle extracts after exposure revealed clear differences in the cuticular hydrocarbon profiles associated with exposure to spreading agents: the alkane n-hexacosane was present in all extracts but was detected in greater relative abundance from bees exposed to Silwet L-77© and Alligare 90©. To support wild bee conservation efforts, we recommend substituting alcohol-based spreaders for siloxane-based spreaders when possible. In addition, certain cuticular hydrocarbons may be useful as biomarkers of previous exposure to certain surfactants, which can aid investigations evaluating causes of bumblebee decline across landscapes.

A novel pesticide has lethal consequences for an important pollinator

Wild bees pollinate crops and wildflowers where they are frequently exposed to pesticides. Neonicotinoids are the most commonly used insecticide globally, but restrictions on their use and rising pest resistance have increased the demand for alternative pesticides. Flupyradifurone is a novel insecticide that has been licenced globally for use on bee-visited crops. Here, in a semi-field experiment, we exposed solitary bees (Osmia lignaria) to a commercial pesticide formulation (Sivanto Prime) containing flupyradifurone at label-recommended rates. We originally designed the experiment to examine sublethal effects, but contrary to our expectations, 100 % of bees released into pesticide-treated cages died within 3 days of exposure, compared to 0 % in control plots. Bees exposed to flupyradifurone a few days after the initial application survived but endured prolonged sublethal effects, including lower nesting success, impairment to foraging efficiency, and higher mortality. These results demonstrate that exposure to this novel insecticide poses significant threats to solitary bees and add to a growing body of evidence indicating that this pesticide can have negative impacts on wild bees at field-realistic concentrations. In the short-term, we recommend that commercial formulations containing flupyradifurone should be restricted to non-flowering crops while a reassessment of its safety can be conducted. In the long-term, environmental risk assessors should continue to develop risk assessments that are truly holistic and incorporate the ecological and life history traits of multiple pollinator species.