A new cage design to test pesticide impacts on honey bees via toxicant exposure through sucrose, pollen and beeswax simultaneously

Abstract

Western honey bees (Apis mellifera) are exposed to pesticides via nectar/honey, pollen and beeswax. The impacts of honey bee exposure to pesticides via pollen or beeswax currently are not considered in pesticide risk assessments. Correspondingly, we developed an in vitro method through which one can expose adult honey bees to pesticide residues in all matrices simultaneously. The design requires modifying in vitro cages to accommodate a pollen paste feeder and beeswax, determining the appropriate concentration of a toxic standard (dimethoate) needed in both matrices to kill 50 % of exposed adult honey bees (positive control), and integrating the test substances into the matrices consistently and evenly. We established five concentrations of dimethoate, a solvent control (acetone) and a negative control for sucrose water, pollen paste, and beeswax. Each dose was tested with three cages, 10 bees/cage, following EPA and OECD guidelines for Tier 1 tests. Mortality was significantly different between bees in the treatment and control groups at 0.1875–3 μg/g dimethoate in sucrose water, 48–192 μg/g in pollen, and 30–120 μg/g in beeswax. We conducted an additional experiment by adding the highest recorded levels of imidacloprid detected in honey (represented by sucrose water), pollen, and beeswax to each matrix as a proof-of-concept for our proposed method. Survival of bees in this worst-case scenario treatment was significantly lower than that in the solvent control group. The addition of pollen and beeswax as matrices for test substance screening will increase the biological relevance of honey bee toxicity tests.