Abstract
Bees are considered to be threatened globally, with severe overwinter losses of the most important commercial pollinator, the Western honeybee, a major concern in the Northern Hemisphere. Emerging infectious diseases have risen to prominence due to their temporal correlation with colony losses. Among these is Deformed wing virus (DWV), which has been frequently linked to colony mortality. We now provide evidence of a strong statistical association between overwintering colony decline in the field and the presence of DWV genotype-B (DWV-B), a genetic variant of DWV that has recently been shown to be more virulent than the original DWV genotype-A. We link the prevalence of DWV-B directly to a quantitative measure of overwinter decline (workforce mortality) of honeybee colonies in the field. We demonstrate that increased prevalence of virus infection in individual bees is associated with higher overwinter mortality. We also observed a substantial reduction of infected colonies in the spring, suggesting that virus-infected individuals had died during the winter. Our findings demonstrate that DWV-B, plus possible A/B recombinants exhibiting DWV-B at PCR primer binding sites, may be a major cause of elevated overwinter honeybee loss. Its potential emergence in naïve populations of bees may have far-reaching ecological and economic impacts.
Highlights
Insect pollination, which is carried out mostly by bees, is required for 75% of all food crops[1]; the global value of insect pollination in 2005 has been estimated at €153 billion[2], this is likely to be an underestimate[3]
Pathogens may be major contributors to overwinter colony losses (OCL). Among those that have been implicated in colony decline are several positive ssRNA viruses: Kashmir bee virus (KBV)[12]; Slow bee paralysis virus (SBPV)[23]; Israeli acute paralysis virus (IAPV)[11]; Acute bee paralysis virus (ABPV)[24, 25]; Deformed wing virus (DWV)[12, 24,25,26]; microsporidia, Nosema ceranae, an emerging gut parasite from Asia[13, 27]; and V. destructor, due to its association with several of the viruses[28]
Apart from chronic bee paralysis virus (CBPV), which occurred rarely in both autumn and spring, only viruses belonging to the DWV complex and Black queen cell virus (BQCV) could be detected by multiple ligation probe amplification (MLPA) (Supplementary Table S1)
Summary
Insect pollination, which is carried out mostly by bees, is required for 75% of all food crops[1]; the global value of insect pollination in 2005 has been estimated at €153 billion[2], this is likely to be an underestimate[3]. The emergence of several infectious diseases has coincided with elevated honeybee colony losses[11,12,13] Notable among these are positive single stranded RNA (positive ssRNA) viruses that have risen to prominence since the arrival of a novel biological vector from Asia, the ectoparasitic mite Varroa destructor. Pathogens may be major contributors to OCL Among those that have been implicated in colony decline are several positive ssRNA viruses: Kashmir bee virus (KBV)[12]; Slow bee paralysis virus (SBPV)[23]; Israeli acute paralysis virus (IAPV)[11]; Acute bee paralysis virus (ABPV)[24, 25]; Deformed wing virus (DWV)[12, 24,25,26]; microsporidia, Nosema ceranae, an emerging gut parasite from Asia[13, 27]; and V. destructor, due to its association with several of the viruses[28]. DWV-B has been recorded in Europe, Africa and Asia[34,35,36,37] and is widespread in UK33, its role in OCL is currently unknown
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