Suitability of the trait postcapping stage of brood for selecting varroa-resistant honey bees

The ectoparasitic mite Varroa destructor poses the most serious threat to the bee keeping industry. Varroa destructor females reproduce only in the caped brood under substantial time constraints. Within the 12 days postcapping stage of the host, offspring of the mite have to complete their development completely; otherwise they do not survive outside the brood cell. Clearly, the faster the development of bees, the fewer offspring mites are produced. Consequently selection for a shorter post capping stage of bee brood was suggested as a suitable goal for breeding resistant honeybees. Varroa-infested brood is strongly handicapped and not able after emerging to participate in colony duties. The objective of the current study was to investigate, whether also the postcapping stage is affected by Varroa infestation. To study this, time of cells capping was monitored at 2-h interval and emerging of honeybee workers was observed by an infra-red barrier system and (in the second experiment) by video observations. The post capping stage of Varroa artificially infested brood and non infested brood were compared. Varroa mite without or less reproduction didn’t influence post capping stage significantly. Normal reproduction of mites or multiple infestations lengthen post capping stage significantly and result partly in bees unable to emerge alone. These cells are uncapped by bees from the outside of the cell on average 24 h after normal emerging. This extra time can be used by mites’ offspring to complete their development. In addition selection towards shorter post capping stage results in worker bees with reduced vitality, which are likely to be even more affected by Varroa parasitism. Consequently, selection for a shorter post capping stage of
honeybee brood doesn’t seem a suitable trait to breed honeybees resistant to Varroa destructor.

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