Toxicological and immunohistochemical testing of honeybees after oxalic acid and rotenone treatments

Bees removed capped brood and young larvae from combs at a greater rate after a rotenone treatment than after an oxalic acid (OA)/sucrose treatment. Rotenone (1%) caused 75.2% of capped brood to be removed, OA (3%) 18.7% and a control treatment, 13.3%. Caged worker bees treated with a 1% rotenone powder, a 3% OA or with a control solution had mortality rates of 10.9%, 5.1% and 1.9% respectively. Rotenone (1%) significantly affected the mortality of brood and adult bees whereas OA (3%), did not. Solutions of 3% OA/32% sucrose, 3.4% OA/47.6% sucrose, 3.7% OA/27.1% sucrose (w/w) and a 32% sugar solution applied to adult bees resulted in death rates of 11%, 14%, 11.2% and 6.5% respectively. Individually treated bees consumed more of a 3% OA solution than solutions with higher OA concentrations. A TUNEL assay detected necrotic cell death in 69% of bee midgut cells 24 h after an OA treatment. Normal cell turnover is approximately 8%