Sublethal chronic exposure and lethal acute exposure to indoxacarb-based insecticide cause histopathological and cytopathological changes in the midgut of Apis mellifera (Hymenoptera: Apidae)

Abstract

Bees play essential roles in ecosystems, and agriculture benefits from their pollination services. However, populations of species like Apis mellifera are in decline, with insecticides being a major contributing factor. During foraging, bees can be acutely exposed to insecticides in the field or chronically to contaminated nectar and pollen, which they transport to the hive. While insecticides often target specific organs, non-target organs such as the midgut can also be affected. Indoxacarb is a pro-insecticide with neurotoxic activity that requires enzymatic activation and is considered safe for many non-target organisms. This study assessed the effects of acute-lethal and chronic-sublethal oral exposure to an indoxacarb-based insecticide on the midgut of Africanized A. mellifera workers. We estimated a concentration-mortality curve and conducted histopathological and cytopathological analyses using LC₅₀ for 24 h and LC₅/₁₀₀ for 8 days in 3-day-old workers. Both treatments caused alterations consistent with damage to the midgut, including vacuolization, apical cell protrusions, cell elimination, and epithelial disorganization. Ultrastructural analysis revealed cytotoxicity, vacuolization with autophagic morphology, reticulum endoplasmic with typical characteristics of vesiculated rough reticulum, and basal labyrinth disorganization. These results demonstrate, for the first time, that, even sublethal concentrations, the indoxacarb-based insecticide cause alterations in intestinal histology and ultrastructure, consistent with detrimental damage to bee health. This suggests that prolonged exposure to indoxacarb-based insecticide residues has the potential to negatively affect worker bees and, consequently, the colony.