Effects of 'inactive' ingredients on bees

•Widely used 'inactives or inerts' in agrochemicals are toxic to honey bees.•Lack of disclosure of formulation ingredients in major products limits risk analysis.•Formulations are generally more toxic to bees than active ingredients.•Most risk assessment for pollinators is performed without formulation ingredients.•Formulation composition and not just the dose of active ingredient makes the poison.

Honey bees are sensitive to widespread co-formulants used in agrochemicals, and evaluation of the role of these 'inerts or inactives' in pollinator decline is only in its formative stages. Lack of disclosure of formulation ingredients in major products and lack of adequate methods for their analysis constrain the assessment of total chemical load and agrochemical exposures on bees. Most studies to document pesticide effects on honey bees are performed without the formulation or other relevant spray adjuvant components used to environmentally apply the toxicant. Formulations are generally more toxic than active ingredients, particularly fungicides, by up to 26,000-fold based on published literature. Some 'inactive' candidates for future risk assessment for pollinators include the organosilicone surfactants and the co-solvent N-methyl-2-pyrrolidone.