Sulfoxaflor (SULF), a well-known alternative for the banned neonicotinoids, is not environmentally persistent, yet numerous studies using field-realistic levels have demonstrated its detrimental impact on honey bee colonies. Despite this, even just a limited number of studies have addressed its residue-level effects on the physiological and immunological biomarkers of foraging honey bees in semi-field conditions. In the present study, we determined the LT50 of sulfoxaflor (Closer (TM) 24% SC) on forager bees in the laboratory at concentrations that were 12 to 300,000-fold lower than the field-recommended concentration. Following that, we exposed bee colonies in a semi-field in-hive experiment for 21 days to a concentration that is 600,000-fold lower than the field-recommended concentration to assess potential effects on the physiological state of honey bee foragers. To do that, a total of six colonies were treated with Closer (TM) (0.3 mu g a.i./L) or control treatment, and the activities of acetylcholinesterase (AChE), glucose oxidase (GOX), and carboxylesterase (CaEs) in head tissues and invertase (IV), alkaline phosphatase (ALP), and glutathione-S-transferase (GST) in the midgut tissues of forager bees were assessed at 5-, 10-, 15-, and 20-day post-exposure. The LT50 results for the least and greatest concentrations of Closer (TM) were 0.37 and 74.3 h, respectively. Furthermore, all measured physiological and immunological biomarkers were negatively impacted in the chronic exposure to 0.3 mu g a.i./L concentration of Closer (TM). This data demonstrated the importance of reviewing the risk assessment of various sulfoxaflor formulations on bees and rephrasing the legislation that governs how beekeepers deal with sulfoxaflor-sprayed fields.
