Abstract
BackgroundNumerous surveys reveal high levels of pesticide residue contamination in honey bee comb. We conducted studies to examine possible direct and indirect effects of pesticide exposure from contaminated brood comb on developing worker bees and adult worker lifespan.Methodology/Principal FindingsWorker bees were reared in brood comb containing high levels of known pesticide residues (treatment) or in relatively uncontaminated brood comb (control). Delayed development was observed in bees reared in treatment combs containing high levels of pesticides particularly in the early stages (day 4 and 8) of worker bee development. Adult longevity was reduced by 4 days in bees exposed to pesticide residues in contaminated brood comb during development. Pesticide residue migration from comb containing high pesticide residues caused contamination of control comb after multiple brood cycles and provided insight on how quickly residues move through wax. Higher brood mortality and delayed adult emergence occurred after multiple brood cycles in contaminated control combs. In contrast, survivability increased in bees reared in treatment comb after multiple brood cycles when pesticide residues had been reduced in treatment combs due to residue migration into uncontaminated control combs, supporting comb replacement efforts. Chemical analysis after the experiment confirmed the migration of pesticide residues from treatment combs into previously uncontaminated control comb.Conclusions/SignificanceThis study is the first to demonstrate sub-lethal effects on worker honey bees from pesticide residue exposure from contaminated brood comb. Sub-lethal effects, including delayed larval development and adult emergence or shortened adult longevity, can have indirect effects on the colony such as premature shifts in hive roles and foraging activity. In addition, longer development time for bees may provide a reproductive advantage for parasitic Varroa destructor mites. The impact of delayed development in bees on Varroa mite fecundity should be examined further.
Highlights
Losses associated with colony collapse disorder (CCD) represent a continuation in sudden and often catastrophic population crashes in honey bee (Apis mellifera) colonies that have become commonplace since the mid 1980s, when two species of parasitic mites were discovered in the United States [1]
In this study we examined the sub-lethal effects of developmental exposure to pesticide residues on worker bees
Experimental combs Frames of treatment brood comb originated from migratory Pacific Northwest beekeeping operations that used miticides and from colonies provided by the USDA- ARS honey bee laboratory, Beltsville, MD that were suspected to have died from Colony Collapse Disorder
Summary
Losses associated with colony collapse disorder (CCD) represent a continuation in sudden and often catastrophic population crashes in honey bee (Apis mellifera) colonies that have become commonplace since the mid 1980s, when two species of parasitic mites were discovered in the United States [1]. Honey bee health decline and colony losses have not been limited to the U.S Many studies in Europe have examined potential correlations between major recent bee losses and pesticide exposure, the class of neonicotinoid insecticides [3,4,5]. Studies from Spain have focused mainly on the effects of Nosema ceranae, a microsporidian pathogen that targets the honey bee midgut and deprives infected bees of nutrients [6]. Pesticide exposure increases honey bee susceptibility to Nosema ceranae spore infection and vice versa [7,8]. Numerous surveys reveal high levels of pesticide residue contamination in honey bee comb. We conducted studies to examine possible direct and indirect effects of pesticide exposure from contaminated brood comb on developing worker bees and adult worker lifespan
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