5.5. Tissue culture
The importance of a viable tissue-culture system for the purification and propagation of honey bee viruses has long been acknowledged. There are two possible approaches to such a system. One is to develop a reliable, immortal honey bee cell line for infection. Only recently has there been any significant progress towards this goal (Bergem et al., 2006; Hunter, 2010; Kitagishi et al., 2011; Gisder et al., 2012). The other approach is to propagate honey bee viruses in existing commercial, heterologous insect cell lines. Many of the honey bee viruses naturally infect other insect hosts, such as other Apis spp., varroa and tropilaelaps parasitic mites, bumble bees, wasps, ants and a range of solitary pollinators (Bailey and Gibbs, 1964; de Miranda et al., 2010a; de Miranda and Genersch, 2010; Ribière et al., 2010; Dainat et al., 2009; Singh et al., 2010; Peng et al., 2011; Li et al., 2011; DiPrisco et al., 2011; Zhang et al., 2012; Evison et al., 2012) and the replication-translation control regions of honey bee virus genomes are active in several commercial Lepidopteran and Dipteran cell lines (Ongus et al., 2006). Protocols for the establishment and maintenance of honey bee and commercial insect cell lines can be found in the BEEBOOK article on cell cultures (Genersch et al., 2013).