Adverse effects of entomopathogenic nematodes on honey bees following foliar application under laboratory conditions

The need for sustainable crop protection has intensified interest in entomopathogenic nematodes (EPNs) as biological alternatives to synthetic agrochemicals. However, their potential non-target effects on pollinators remain poorly characterized, and regulatory approvals often rely on limited data. Here, we provide the first demonstration of adverse effects of foliar-applied Steinernema carpocapsae (Nemastar®) on adult honey bees, Apis mellifera. Using a modified regulatory protocol (USEPA 850.3030), adult honey bees and greater wax moth larvae (Galleria mellonella; positive control) were exposed for 96 h to field-realistic low and high EPN doses (0.25-2.5 × 10⁶ infective juveniles m²) under dry and wet application scenarios. Adult honey bee and greater wax moth larvae mortality was recorded daily. Steinernema carpocapsae significantly reduced survival in both species, with the highest mortality under the wet and high-dose conditions. Nematode infestation and proliferation were confirmed in deceased individuals using White traps and standardized counts, revealing species-, dose-, and application-dependent differences. Our results provide novel evidence that foliar surface application of S. carpocapsae can adversely affect adult honey bees. We recommend restricting foliar applications to nighttime (i.e., after dusk) to reduce the risk of exposure to non-target pollinators. We further emphasize the urgent need for standardized regulatory studies for EPN products to ensure sufficient evidence of environmental safety before approval and widespread use.