Varroa destructor and a threat of viral infections of the honeybee (Apis mellifera L.)

Abstract

Bee viral infections worldwide leading to colonies' depopulation have emerged as a threat to bee keeping. To date, nearly 20 RNA viruses, of Dicistroviridae, Iflaviridae, Nodaviridae families mostly, were detected in honeybee Apis mellifera (O.F. Grobov et al., 2006; C. Runckel et al., 2011). Also DNA viruses have been found, e.g. iridovirus (Iridoviridae), potentially causing losses of bee colonies (J.J. Bromenshenk et al., 2010), Aphid Lethal Paralysis virus (Dicistroviridae), Big Sioux River virus (Dicistroviridae), Lake Sinai Virus strain 1 and 2 (Nodaviridae) (C. Runckel et al., 2011) however, their role in bee mortality has yet to be understood. The most important bee viruses known to date are deformed wing virus (DWV), acute bee paralysis virus, (ABPV), chronic bee paralysis virus (CBPV), Kashmir bee virus, (KBV), sacbrood virus, (SBV), Black queen cell virus (BQCV). These viruses can persist in honey bees (Apis mellifera L.) without apparent symptoms, however, Varroa destructor infestation causes a viral epidemic, diminishing bee colonies. The range of V. destructor, the main viral infections' vector (D. Tentcheva et al., 2004), was confined to that of A. cerana being ecologically balanced. However, not long ago this mite crossed the species barrier from the Asian hive bee A. cerana to our own Western honey bee A. mellifera (R.S. Poltorzhitskaya, 2008). The introduction of V. destructor into the A. mellifera population has become one of the major contributing factors to colony collapse disorder (D. van Engelsdorp et al., 2008; R.M. Johnson et al., 2009; F. Nazzi et al., 2012). Moreover, the mite Varroa affect the immune response and metabolism of honey bees and allow its vectored viruses to propagate to high viral loads. At present there is an objective need for a closer look into bee viruses implicated in bee colony losses reported worldwide. So far as Varroa mite is an obligate parasite of A. mellifera during whole ontogenesis, the Varroa control notably ensures the well-being of bee colonies. In this review, an overview of the world distribution and the impact of the major viruses (DWV, ABPV, CBPV, SBV, BQCV, KBV) on bee health and colony survival is presented. We also discuss approaches to virus control. Overall, the strategy combining new Varroa management practices (A.A. Fedorova et al., 2011), selection of Varroa-resistant bees and novel treatments against viruses will help sustain the honey bee population.