Abstract: Nosema ceranae and pesticide exposure can contribute to honey bee health decline. Bees reared from brood comb containing high or low levels of pesticide residues were placed in two common colony environments. One colony was inoculated weekly with N. ceranae spores in sugar syrup and the other colony received sugar syrup only. Worker honey bees were sampled weekly from the treatment and control colonies and analyzed for Nosema spore levels. Regardless of the colony environment (spores+syrup added or syrup only added), a higher proportion of bees reared from the high pesticide residue brood comb became infected with N. ceranae, and at a younger age, compared to those reared in low residue brood combs. These data suggest that developmental exposure to pesticides in brood comb increases the susceptibility of bees to N. ceranae infection.
"Importantly, the honey bee brood comb pesticide residue levels referred to in this study as "high" are apparently rather commonplace in managed populations of honey bees in the United States (Mullin et al., 2010; Wu et al., 2011). The origins of the pesticide mixtures found in honey bee brood combs likely include in-hive miticides used by beekeepers and various agricultural and environmental sources. It is unclear whether the combination of sub-lethal pesticide exposure during larval development and N. ceranae infection has an additive or synergistic effect, however, this study suggests there is an increased susceptibility to N. ceranae infection in treatment bees which may be due to the added stress of developing in pesticide-laden comb and the possible utilization of critical energetic resources and detoxifying enzymes."
Wu JY, Smart MD, Anelli CM, Sheppard WS (2012) Honey bees (Apis mellifera) reared in brood combs containing high levels of pesticide residues exhibit increased susceptibility to Nosema (Microsporidia) infection, J Invertebr Pathol. 2012 Mar;109(3):326-9.