Abstract
Queen fecundity is a critical issue for the health of honeybee (Apis mellifera L.) colonies, as she is the only reproductive female in the colony and responsible for the constant renewal of the worker bee population. Any factor affecting the queen's fecundity will stagnate colony development, increasing its susceptibility to opportunistic pathogens. We discovered a pathology affecting the ovaries, characterized by a yellow discoloration concentrated in the apex of the ovaries resulting from degenerative lesions in the follicles. In extreme cases, marked by intense discoloration, the majority of the ovarioles were affected and these cases were universally associated with egg-laying deficiencies in the queens. Microscopic examination of the degenerated follicles showed extensive paracrystal lattices of 30 nm icosahedral viral particles. A cDNA library from degenerated ovaries contained a high frequency of deformed wing virus (DWV) and Varroa destructor virus 1 (VDV-1) sequences, two common and closely related honeybee Iflaviruses. These could also be identified by in situ hybridization in various parts of the ovary. A large-scale survey for 10 distinct honeybee viruses showed that DWV and VDV-1 were by far the most prevalent honeybee viruses in queen populations, with distinctly higher prevalence in mated queens (100% and 67%, respectively for DWV and VDV-1) than in virgin queens (37% and 0%, respectively). Since very high viral titres could be recorded in the ovaries and abdomens of both functional and deficient queens, no significant correlation could be made between viral titre and ovarian degeneration or egg-laying deficiency among the wider population of queens. Although our data suggest that DWV and VDV-1 have a role in extreme cases of ovarian degeneration, infection of the ovaries by these viruses does not necessarily result in ovarian degeneration, even at high titres, and additional factors are likely to be involved in this pathology.
Highlights
The general decline in managed Apis mellifera L. colonies and beekeepers in Europe and the USA, as well as some other regions in the world, is a major challenge for ensuring adequate pollination of crops and wild plants [1,2,3,4,5]
We received a total of 130 mated queens (Apis mellifera L.) from French beekeepers between 2007 and 2009
The tissues from all 130 queens were processed for RNA extraction, in order to quantify the amount of deformed wing virus RNA using quantitative RT-qPCR
Summary
The general decline in managed Apis mellifera L. colonies and beekeepers in Europe and the USA, as well as some other regions in the world, is a major challenge for ensuring adequate pollination of crops and wild plants [1,2,3,4,5]. Among the numerous possible causes involved in colony weakness and death, poor queen quality is often reported by beekeepers as a principal contributing factor [4]. This includes problems associated with low fecundity and untimely requeening events [6,7]. For the honeybee (Apis mellifera L.), the queen is the sole reproductive female of the colony, producing a large number of sterile daughters (worker bees) who perform all the colony maintenance tasks, principally brood care, colony defence, construction and foraging. During the inactive season (winter in temperate climates), the queen reduces its egg-laying activity and winter bees can survive for months on the stored colony food reserves [8,9]. The nutritional stimuli affect the TOR (target of rapamycin) regulatory pathway [11] and trigger an endocrine response manifested by an elevated juvenile hormone titre in queen larvae, compared to worker bee larvae [12]
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