Assessing the safety of two organosulfur compounds derived from onion in western honey bee (Apis mellifera).

Abstract

This work aims to analyse the toxicity of propyl-propane thiosulfinate (PTS) and propyl-propane thiosulfonate (PTSO), two organosulfur compounds, in long-lived winter (also known as diutinus bees) and short-lived spring honey bees. Acute toxicity assays were performed by contact and oral exposure, using the insecticide dimethoate as toxic standard. These compounds are derived from Allium cepa and have previously reported antimicrobial and weak insecticidal activity, and their potential use in crop protection requires a honeybee risk assessment under the new EFSA pollinator protection guidelines. Additionally, the concentrations at which honey bees do not voluntarily ingest each compound were assessed through an antifeedant activity test. In both cohorts, the LD₅₀ of PTS and PTSO are higher than the hypothetical application dose (1 µg/bee). Long-lived winter honey bees were found to be more resistant to both compounds than short-lived spring honey bees. Assessment of the effects of exposure to both compounds combined showed no synergism. Neither cohort voluntarily ingested PTS or PTSO at 10 µg/µl. While partial ingestion was observed at 2 and 4 µg/µl, at 1 µg/µl or lower voluntary ingestion occurred at levels comparable to the control, without any observed mortality. These findings indicate that, at field relevant doses, PTS and PTSO are compatible with honey bee safety under acute exposure and warrant further field and chronic-exposure evaluation.