Hygienic behavior in honey bees (Hymenoptera: Apidae): effects of brood, food, and time of the year.

Hygienic behavior in honey bees is a heritable trait of individual workers that confers colony-level resistance against various brood diseases. Hygienic workers detect and remove dead or diseased brood from sealed cells. However, this behavior is quite rare, with only c.10% of unselected colonies showing high levels of hygiene. Beekeepers can potentially increase this by screening colonies for hygiene and breeding from the best. However, the level of hygiene expressed by a colony is variable, which poses a challenge to colony selection. In this study, we systematically varied two factors thought to be of importance in influencing hygiene levels, "nectar" availability, by feeding or not feeding sucrose syrup, and brood amount, by adding or removing brood, to determine what effect they had on hygienic behavior. We tested 19 colonies repeatedly over a 4-mo period using the freeze-killed brood assay, a standard technique to quantify hygienic behavior. Two days after freeze-killed brood treatment, our colonies showed a wide range of brood removal levels, with colony means ranging from 31.7 +/- 22.5 to 93 +/- 6.9 (mean % +/- SD). Neither the food nor the brood manipulation had an effect on hygiene levels. Colony size and time of year were also nonsignificant. The only significant effect was a three-way interaction between syrup availability, amount of brood, and time of the year, resulting in reduced hygienic behavior early in the season (spring), in colonies with added brood that were not fed sucrose syrup. Overall, these results suggest that hygienic behavior is not greatly affected by environmental conditions typical of a real-life beekeeping, and that screening of colonies can be done anytime without special regard to nectar conditions or brood levels.

Evaluation of Suppressed Mite Reproduction (SMR) Reveals Potential for Varroa Resistance in European Honey Bees (Apis mellifera L.).

In the fight against the Varroa destructor mite, selective breeding of honey bee (Apis mellifera L.) populations that are resistant to the parasitic mite stands as a sustainable solution. Selection initiatives indicate that using the suppressed mite reproduction (SMR) trait as a selection criterion is a suitable tool to breed such resistant bee populations. We conducted a large European experiment to evaluate the SMR trait in different populations of honey bees spread over 13 different countries, and representing different honey bee genotypes with their local mite parasites. The first goal was to standardize and validate the SMR evaluation method, and then to compare the SMR trait between the different populations. Simulation results indicate that it is necessary to examine at least 35 single-infested cells to reliably estimate the SMR score of any given colony. Several colonies from our dataset display high SMR scores indicating that this trait is present within the European honey bee populations. The trait is highly variable between colonies and some countries, but no major differences could be identified between countries for a given genotype, or between genotypes in different countries. This study shows the potential to increase selective breeding efforts of V. destructor resistant populations.

Comparing alternative methods for holding virgin honey bee queens for one week in mailing cages before mating.

In beekeeping, queen honey bees are often temporarily kept alive in cages. We determined the survival of newly-emerged virgin honey bee queens every day for seven days in an experiment that simultaneously investigated three factors: queen cage type (wooden three-hole or plastic), attendant workers (present or absent) and food type (sugar candy, honey, or both). Ten queens were tested in each of the 12 combinations. Queens were reared using standard beekeeping methods (Doolittle/grafting) and emerged from their cells into vials held in an incubator at 34C. All 12 combinations gave high survival (90 or 100%) for three days but only one method (wooden cage, with attendants, honey) gave 100% survival to day seven. Factors affecting queen survival were analysed. Across all combinations, attendant bees significantly increased survival (18% vs. 53%, p<0.001). In addition, there was an interaction between food type and cage type (p<0.001) with the honey and plastic cage combination giving reduced survival. An additional group of queens was reared and held for seven days using the best method, and then directly introduced using smoke into queenless nucleus colonies that had been dequeened five days previously. Acceptance was high (80%, 8/10) showing that this combination is also suitable for preparing queens for introduction into colonies. Having a simple method for keeping newly-emerged virgin queens alive in cages for one week and acceptable for introduction into queenless colonies will be useful in honey bee breeding. In particular, it facilitates the screening of many queens for genetic or phenotypic characteristics when only a small proportion meets the desired criteria. These can then be introduced into queenless hives for natural mating or insemination, both of which take place when queens are one week old.