B. Cornelissen

Winter Survival of Individual Honey Bees and Honey Bee Colonies Depends on Level of Varroa destructor Infestation

Background Recent elevated winter loss of honey bee colonies is a major concern. The presence of the mite Varroa destructor in colonies places an important pressure on bee health. V. destructor shortens the lifespan of individual bees, while long lifespan during winter is a primary requirement to survive until the next spring. We investigated in two subsequent years the effects of different levels of V. destructor infestation during the transition from short-lived summer bees to long-lived winter bees on the lifespan of individual bees and the survival of bee colonies during winter. Colonies treated earlier in the season to reduce V. destructor infestation during the development of winter bees were expected to have longer bee lifespan and higher colony survival after winter. Methodology/Principal Findings Mite infestation was reduced using acaricide treatments during different months (July, August, September, or not treated). We found that the number of capped brood cells decreased drastically between August and November, while at the same time, the lifespan of the bees (marked cohorts) increased indicating the transition to winter bees. Low V. destructor infestation levels before and during the transition to winter bees resulted in an increase in lifespan of bees and higher colony survival compared to colonies that were not treated and that had higher infestation levels. A variety of stress-related factors could have contributed to the variation in longevity and winter survival that we found between years. Conclusions/Significance This study contributes to theory about the multiple causes for the recent elevated colony losses in honey bees. Our study shows the correlation between long lifespan of winter bees and colony loss in spring. Moreover, we show that colonies treated earlier in the season had reduced V. destructor infestation during the development of winter bees resulting in longer bee lifespan and higher colony survival after winter.

Interactive effect of reduced pollen availability and Varroa destructor infestation limits growth and protein content of young honey bees

Varroa destructor in combination with one or more stressors, such as low food availability or chemical exposure, is considered to be one of the main causes for honey bee colony losses. We examined the interactive effect of pollen availability on the protein content and body weight of young bees that emerged with and without V. destructor infestation. With reduced pollen availability, and the coherent reduced nutritional protein, we expected that V. destructor infestation during the pupal stage would have a larger negative effect on bee development than without infestation. Moreover, when raised with ample pollen available after emergence, infested pupae were expected not to be able to compensate for early losses due to V. destructor. We found that both V. destructor infestation and reduced pollen availability reduced body weight, abdominal protein level, and increased the head to abdomen protein ratio. The availability of pollen did indeed not result in compensation for reduced mass and protein content caused by V. destructor infestation in young bees after 1 week of their adult life. Both V. destructor and nutrition are top concerns for those studying honey bee health and this study demonstrates that both have substantial effects on young bees and that ample available pollen cannot compensate for reduced mass and protein content caused by V. destructor parasitism.

How honey bees of successive age classes are distributed over a one storey, ten frames hive

Summary In honey bee studies focusing on physiology, disease diagnosis or bio indication, bees are sampled from the colony. This raises the question of where in the colony samples must be taken from for specific study objectives. In this study we recorded where bees of known age are found in the hive. We recorded in a single brood box with ten frames in August that the mean proportion of bees of one (41%), two (23%), three (17%), four (11%) and five (8%) week old bees did not differ between frames. Additionally we found that there was a significant mortality of young bees in the first week after emergence. This may be partly due to the study set up but is also a natural phenomenon.

Queen survival and oxalic acid residues in sugar stores after summer application against Varroa destructor in honey bees (Apis mellifera)

Summary Methods using oxalic acid (OA) to control Varroa destructorin honey bee (Apis mellifera) colonies are widely applied. In this study, the effects of an OA spray application in early summer on the survival of young and old queens, and on OA residues in sugar stores were investigated. A questionnaire among beekeepers was used to determine the ‘normal’ and ‘acceptable’ queen mortality as a result of beekeeper activities. ‘Acceptable’ queen mortality (4.1 ± 0.1% (n = 11)) did not differ from queen mortality after OA spray application (2.7% for old and 3.8% for young queens). ‘Normal’ queen mortality (1.1 ± 0.4% (n = 11) and 4.2 ± 0.1% (n = 11) for old and young queens, respectively) also did not differ from queen mortality after spraying OA. OA found in sugar stores of colonies sprayed with OA (94 ± 7 mg/kg (n = 8)) did not differ from control colonies (80 ± 4 mg/kg (n = 9)). Finding OA residues in both groups was probably due to bees foraging on chestnut (Castanea sativa) trees. We conclude that OA spray application in periods without brood during spring and summer poses little danger to honey bee queens and that in sugar stores harvested in summer, OA residues are within the limits of natural variability.