Transportation and pollination service increase abundance and prevalence of Nosema ceranae in honey bees (Apis mellifera)

Nosema ceranae affects honey bee physiology and behavior adversely and is also recently shown to increase its infection probability when bees were exposed to pollen with fungicides in a lab study. However it is not clear if transportation stress plus the subsequent pollination service would increase N. ceranae prevalence and abundance. 

Fourteen colonies were randomly divided into two groups. A group of “transported and pollinating colonies” (TP) was moved to provide pollination for blueberry for 11 days, 138 km away. A group of “stationary colonies” (S) was not moved (at East Lansing, MI) and served as the control during the same time. Fifteen foragers were sampled per colony from all 14 colonies using a bee vacuum, 1 day before transportation took place ((TP₀ and S₀) and then 7 days after the bees were moved back (TP₁ and S₁). Spore loads in the midgut in individual bees were then determined and we also ran PCR to verify the spores to be N. ceranae.

There was no significant difference in infection rates between TP₀ and S₀ (T=0.013, 2-tailed test, P=0.99) and between S₀ and S₁ (T=0.43, 2-tailed test, P=0.67) (Fig. 1A). This suggests that TP and S groups had the same Nosema prevalence at the beginning of the experiment. In addition, prevalence of S group did not change before and after transportation and pollination. However, we found a significantly higher Nosema prevalence in TP₁ than S₁ (T=2.14, 1-tailed test, P=0.027), suggesting that transportation and/or pollination caused a higher infection rate in workers.

Nosema abundance followed a similar pattern (Fig. 1B).  There was no significant difference between the TP₀ and S₀ (T=0.44, 2-tailed test, P=0.67), and between S₀ and S₁ (T=0.37, 2-tailed test, P=0.71). Therefore TP and S had the same Nosema abundance before bees were moved for pollination service and S colonies did not change their Nosema abundance during the same period.  However Nosema abundance was significantly higher in TP₁ than TP₀ (T=1.72, 1-tailed test, P=0.05).
Our small experiment suggests that transportation and pollination affects N. ceranae prevalence and abundance, perhaps by affecting honey bees’ immune system. It is not clear if these effects were due to transportation alone, pollination alone, or both combined.  This research was supported by a Managed Pollinator CAP USDA NIFA Grant #20098521805718.