Inert ingredients in pesticides may impair foraging behavior in honey bees (Apis mellifera ligustica)

Honey bees are exposed to a wide range of agricultural pesticides, which contain supposedly inert ingredients as well as the biologically active ingredient(s). Here, we present evidence that these inert ingredients may impair the foraging behavior of honey bees. Proboscis extension response (PER) assays were conducted on groups of bees fed one of three sucrose-based diets: sucrose only, active ingredient only, and formulation containing active ingredients and inert ingredients. Bees fed the active + inert diet had significantly lower learning ability. The PER assay is a reliable test of learning ability, which is important for foraging workers. Inert ingredients may therefore have a substantial impact on the ongoing decline of honey bees independent of the much more widely studied active ingredients.