Evaluation of Apis mellifera brain morphophysiology in response to titanium dioxide nanoparticles and deltamethrin co-exposure

Abstract

Honeybees are important insects, both economically and as pollinators. While foraging, bees can come in contact with environmental pollutants such as pesticides, possibly in combination with other xenobiotic compounds that may compromise bee health. Our current study investigated the acute exposure to nanosized titanium dioxide, a common additive in food, cosmetics, paints and agricultural products, along with deltamethrin (DLT), a well-known pyrethroid pesticide. The effects of binary exposure to titanium dioxide nanoparticles (TiO₂-NPs) nanoparticles at concentrations of 25, 50, 75 and 100 μg/mL with DLT were noted on Apis mellifera brain histology along with their possible synergism. In DLT- and combined TiO₂-NP-DLT treated bees, survival rates were lowered and several histological alterations were observed including an increased number of cells with pyknotic nuclei, along with cytoplasmic vacuolization, chromatin compaction and degeneration indicating autophagic activity and a decrease in the cross-sectional area of nanoparticle-treated mushroom body calyces. A synergistic relationship between TiO₂-NPs and DLT was revealed, while LD₅₀ for combined TiO₂-NP-DLT treatment was 0.101, 0.09 and 0.02 μg/bee at 24, 48 and 72 h, respectively. In summary, results demonstrate that TiO₂-NP and DLT co-exposure can induce damage in bee brain structures at higher concentrations, which indicates an additional risk factor for bee health in the field.