Honey bee venom promotes the immune system and reduces Vairimorpha (Nosema) ceranae infection in honey bees (Apis mellifera L.)

Bee venom (BV) extraction has become a standardized practice, characterized by being safe, simple, and causing no harm to bees. Though it demonstrated significant antimicrobial activity, its potential activity against honey bee pathogens have yet to be investigated. Therefore, we investigated for the first time in a controlled laboratory setting the effectiveness of BV administration in sugar syrup against Vairimorpha (Nosema) ceranae, a globally widespread fungal disease of honey bees. To do this, we first determined the BV lethal concentration (LC₅₀), after which newly emerged bees were inoculated with V. ceranae spores (10⁵) or/and chronically fed sugar syrup containing BV at LC₁₀ (0.24 mg/mL) or LC₂₀ (0.34 mg/mL) ad libitum for 12 days. The effects on bee longevity (time to death) were studied. The intensity of V. ceranae and total hemocyte count (THC) were also studied 6 and 12 days after infection. The expression of four antimicrobial peptides (AMPs) encoding genes (defensin1, apismin, hymenopteacin, and PGRPS2) was also measured after 6 days in midgut tissues. We discovered that BV increased bee survival and significantly reduced Vairimorpha intensity. This effect was associated with an increase in THC as well as the expression of the AMP-encoding genes studied. BV’s effects appeared to be concentration- and time-dependent, with a more profound decrease in Vairimorpha intensity at day 12, especially in bees fed BV at LC₂₀. These findings highlight BV’s potent immunomodulatory role against fungal pathogens in honey bees, and its potential role against other bacterial and viral pathogens should be investigated.