Krzysztof Olszewski
Biology, productivity and resistance to Varroa destructor of bee colonies kept on small-cell combs
Zeszyt 372, ss. 148
There are grounds to support the hypothesis that keeping bee colonies on small-cell combs (a cell width of 4.90 mm) may enhance mechanisms of resistance to V. destructor. This finding could be used in attempts to maximise selection efficiency with regard to increasing resistance to this parasite. An elevated V. destructor resistance of bee colonies kept on small-cell combs has been only confirmed in non-European honey bee subspecies. In Europe, keeping bee colonies on small-cell combs is not an assumed practice.
Bee colonies maintained on small-cell combs were compared with controlcolonies kept on combs with cells in a standard size (a cell width of 5.50 mm). The colonies kept on small-cell combs were subjected to the influence of the V. destructor parasite resulting from non-treatment of varroosis, whereas the colonies kept on standard-cell combs were divided into two control groups – a treated one and an untreated one. The brood and bees in the small-cell combs and in the standard-size combs were reared in two types of fostering colonies: 1) those kept on small-cell combs and 2) those kept on standard-cell combs. Morphometric, biological and economic traits of the brood, individual bees and entire colonies, as well as the resistance of the bee colonies to V. destructor were analysed. Independently from the foster colony (kept on small-cell or standard-cell combs), rearing bees in small-cell combs significantly reduced the post-capping stage and the total duration of the preimaginal ontogenetic stages. The small-cell colonies were only slightly inferior to the treated standard-cell colonies with regard to winter hardiness, spring colony build-up and honey yield. Simultaneously, they performed much better than the untreated colonies kept on standard cell combs. This shows that keeping colonies on small-cell combs in combination with survival selection in an environment where the parasite is not suppressed (parasite pressure) leads to increased tolerance of V. destructor and largely compensates for the fall in productivity caused by heavy infestation with the mite. The increased V. destructor tolerance of the colonies kept on small-cell combs as opposed to that of the untreated standard-cell colonies stemmed from a combination of a number of mechanisms, without a dominant role of any individual one of them. The combination was made up of: 1) a predilection of V. destructor females for drone brood as opposed to worker brood due to a considerable difference in cell width between the worker combs and drone combs, 2) a higher percentage of infested cells without females in the advanced deutonymph stage as a result of a shortened post-capping stage, 3) elevated mortality of V. destructor males in worker cells as compared with drone cells due to tighter cell filling by pupae (cell fill factor). The ability of the colonies kept on small-cell combs to survive without anti-varroosis treatment was found to be hereditary. That is why it can be taken advantage of in selection of V. destructorresistant bees.
The present author found that keeping bee colonies on small-cell combs enhanced the effect of numerous natural resistance mechanisms against V. destructor and, consequently, also the survival rate of bee colonies keept in Europe. It is the first time that grounds have been laid in Europe for taking advantage of keeping bees on small cell combs as a natural auxiliary method in a selection oriented on obtaining resistance to the V. destructor parasite which is widely considered to be one of the principal causes of mass losses among bee colonies worldwide.