Suppression of immune response to infection in honey bees
Belzunces' observations have been recently substantiated by Pettis et al..14 They demonstrated increased susceptibility of newly emerged worker bees to the gut pathogen Nosema ceranae following exposure of honey bee colonies during three brood generations to imidacloprid dosages of 5 ppb and 20 ppb (which are exposures below the levels demonstrated to cause effects on longevity or foraging in adult honey bees). The microsporidian pathogen Nosema ceranae
targets the honeybee midgut and deprives infected bees of nutrients. Thus, they have a much greater chance of dying prematurely. Although residues of imidacloprid were found in bee bread and bees from exposed colonies, and increased in direct and expected proportion to the concentrations in the treated protein patties, newly emerged bees that were
subsequently shown to be more susceptible to Nosema ceranae tested negative for imidacloprid. Therefore, the test bees could only have received pesticide exposure during larval development, and pesticide exposure to test bees could only have been indirectly from brood food from nurse bees. The evidence from these experiments shows that immune suppression by imidacloprid can occur in the absence of detectable imidacloprid residues.
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