Lethal and sub-lethal effects of bentazone-based herbicide on honey bee workers ( Apis mellifera )

Herbicide exposure can have detrimental consequences for honey bees, Apis mellifera L., ranging from lethal to sub-lethal effects. A comprehensive understanding of the impacts of herbicide on this insect species is crucial for their protection. In the present study, the effects of lethal and sub-lethal concentrations of a bentazone-based herbicide were assessed on survival, food consumption, body weight, head protein content, acetylcholinesterase (AChE) activity and midgut histology in worker bees. The acute oral toxicity assays showed that LC50 values of bentazone-based herbicide on forager bees were 4.077, 3.747, and 3.579 mg mL−1 after 48, 72, and 96 h, respectively. In a chronic toxicity test, newly emerged bees were fed sugar syrup that was herbicide-free (control), sugar syrup that contained a high sub-lethal concentration of bentazone-based herbicide [0.716 mg mL−1 (1/5 the 96-h LC50)], and low concentration [0.358 mg mL−1(1/10 the 96-h LC50)] for 21 days. Bees exposed to the high concentration of bentazone-based herbicide experienced significantly lower survival rates and tended to have reduced body weights compared to both control bees and those exposed to the low concentration. Pollen consumption was notably reduced at both tested concentrations. Both concentrations of bentazone-based herbicide also reduced AChE activity and head protein content in bees. Exposure to bentazone-based herbicide resulted in significant damage to the cellular structure of honey bee midguts. This is the first study on the adverse effects of bentazone-based herbicide on A. mellifera health at sub-lethal levels.