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.

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SUMMARYDetection and assessment of varroa infestations in honey bee colonies are important for successful beekeeping. We examined the use of inert dusts to dislodge mites from adult honey bees that were isolated from their nest. Six dusts (powdered sugar, fine sugar, wheat flour, talcum powder, corn starch and baking soda) were evaluated for their ability to dislodge mites from adult bees collected in jars. We obtained the highest recovery rate with powdered sugar (92.9 ± 5.5%) and talcum powder (84.0 ± 5.6%). We also examined mite survival after recovery with inert dusts and compared it to mite survival after recovery from brood. After 24 h mite survival was significantly greater when mites were recovered with corn starch, powdered sugar, and from brood (F = 22.88, d.f. = 6,35, P <0.0001). Finally, ether and powdered sugar were compared as tools for detecting and assessing the degree of infestation. Powdered sugar did not differ from ether in detecting or assessing low (1-5 mites per sample) infestation levels (F = 2.81, d.f. = 1,49, P = 0.1). At medium (6-30 mites per sample) and high (> 30 mites per sample) infestation levels, more mites were recovered with powdered sugar (medium: F = 14.28, d.f. = 1,29, P = 0.008; high: F = 6.34, d.f. = 1,17, P = 0.023).

We evaluated three concentrations of tebufenpyrad (17.5, 15 and 12.5%) in strip formulations for controlling varroa mites, Varroa destructor Anderson and Trueman (2000), in honey bee colonies. We also included colonies treated with Apistan, CheckMite+, and untreated colonies in our evaluation. The three concentrations we evaluated reduced varroa populations but also reduced the amount of brood and adult bees when compared with untreated colonies and colonies treated with Apistan or CheckMite+. Alternative delivery methods, lower concentrations of tebufenpyrad, and the evaluation of related compounds are logical next steps in evaluating the varroacidal potential of tebufenpyrad and related compounds.

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