Beside many beneficial applications in industry, agriculture and medicine, nanoparticles (NPs) released into the environment might cause adverse effects. In the present study, effects of exposure to sublethal concentrations of PbO and CdO NPs, either separately or in combination on honey bee (A. mellifera) workers were assessed. Honey bee workers were fed
sugar syrup contained (20% of LC50) of CdO (0.01 mg ml-1) and PbO (0.65 mg ml-1) NPs either separately or combined for nine days under laboratory conditions. Control bees were fed 1.5 M
sucrose syrup without NPs. Effects on histological and cellular structure of mid gut cells were investigated using light and electron microscope. Percentages of incidence of apoptosis or/and
necrosis in mid gut cells were also quantified by use of flow cytometry. Rapture of the peritrophic membrane (PM) was among the most observed histopathological alteration in bees fed
sugar syrup contained CdO NPs separately or combined with PbO NPs. Common cytological alterations observed in epithelial cells were irregular distribution or/and condensation of nuclear
chromatin, mitochondrial swelling and lysis, and rough endoplasmic reticulum (rER) dilation, fragmentation, and vesiculation and were quite similar in all treated groups compared to control. The greatest incidence (%) of
necrosis was observed in bees fed the diet that contained CdO NPs alone. The greatest % of both apoptosis and
necrosis was observed in bees fed
sugar syrup spiked with sublethal concentrations of both
metal oxide NPs. Joint action of the binary mixture of Cd and Pb
oxide NPs on honey bees was concluded to be antagonistic. Collectively, exposure of honey bees to these
metal oxide NPs even at sublethal concentrations will adversely affect viability of the colony and further studies are still required to determine the effects of these
metal oxide NPs on behavior and pollination ecology of honeybees.