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.
In the honey bee, hygienic behaviour, the removal of dead or diseased brood from capped cells by workers, is a heritable trait that confers colonylevel resistance against brood diseases. This behaviour is quite rare. Only c. 10% of unselected colonies show high levels of hygiene. Previous studies suggested that hygiene might be rare because it also results in the removal of healthy brood, thereby imposing an ongoing cost even when brood diseases are absent. We tested this hypothesis by quantifying hygienic behaviour in 10 colonies using a standard technique, the freeze-killed brood (FKB) bioassay. At the same time, we also quantified the removal of untreated brood. The study colonies showed a wide range in hygienic behaviour, removing 19.7-100% of the FKB. The removal of untreated brood ranged from 2% to 44.4%. However, there was no correlation between the two removal rates for any of the four age groups of untreated brood studied (eggs, young larvae, older larvae from uncapped cells and larvae/pupae from capped cells). These results do not support the cost-to-healthy-brood hypothesis for the rarity of hygienic behaviour.
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.
SummaryHoney bee mating cannot be directly controlled in the same way as in many agriculturally important animals. Instrumental insemination is, however, possible and can be used as an aid in selective breeding. Hygienic behaviour, in which worker bees detect and remove dead or diseased brood from capped cells, is a heritable trait that confers colony-level resistance against brood diseases. Using the freeze-killed brood (FKB) bioassay we compared the levels of hygiene in colonies headed by daughter queens reared from hygienic mother colonies that were either instrumentally inseminated with sperm from drones reared from hygienic colonies or allowed to mate naturally with naturally-occurring drones. Hygiene levels were significantly higher in the colonies of the instrumentally inseminated queens than in the colonies of the naturallymated queens. However, the hygiene levels in the naturally-mated colonies were encouragingly high and indicate that supplying beekeepers with naturally-mated queens, or virgin queens to mate locally, can result in colonies with high levels of hygiene.El efecto de una generación de apareamiento controlado sobre la expresión del comportamiento higiénico en las abejas melíferas Resumen El apareamiento de la abeja de la miel no puede ser controlado directamente de la misma forma que se hace en muchos animales de importancia agrícola. La inseminación instrumental es, sin embargo, posible y puede ser utilizada como ayuda en la cría selectiva. El comportamiento higiénico, en el que las abejas obreras detectan y eliminan la cría muerta o enferma de las celdas operculadas, es un rasgo hereditario que confiere resistencia al nivel de colonia contra enfermedades de la cría. Utilizando el bioensayo de congelar la cría para matarla (BCM) se compararon los niveles de higiene en las colonias gobernadas por hijas de reinas criadas en colonias madre higiénicas que fueron inseminadas instrumentalmente con esperma de zánganos criados de colonias higiénicas o a las que se dejó aparearse naturalmente con zánganos de origen natural. Los niveles de higiene fueron significativamente mayores en las colonias de las reinas inseminadas instrumentalmente que en las colonias de las reinas apareadas naturalmente. Sin embargo, los niveles de higiene en las colonias que se aparearon naturalmente fueron alentadoramente altos e indican que suministrar a los apicultores reinas apareadas naturalmente, o reinas vírgenes para que se apareen localmente, puede dar lugar a colonias con altos niveles de higiene.
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.
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