Infectivity of DWV Associated to Flower Pollen: Experimental Evidence of a Horizontal Transmission Route

Abstract

Deformed wing virus (DWV) is a honeybee pathogen whose presence is generally associated with infestation of the colony by the mite Varroa destructor, leading to the onset of infections responsible for the collapse of the bee colony. DWV contaminates bee products such as royal jelly, bee-bread and honey stored within the infected hive. Outside the hive, DWV has been found in pollen loads collected directly from infected as well as uninfected forager bees. It has been shown that the introduction of virus-contaminated pollen into a DWV-free hive results in the production of virus-contaminated food, whose role in the development of infected bees from virus-free eggs has been experimentally demonstrated. The aim of this study was twofold: (i) to ascertain the presence of DWV on pollen collected directly from flowers visited by honeybees and then quantify the viral load and (ii) determine whether the virus associated with pollen is infective. The results of our investigation provide evidence that DWV is present on pollen sampled directly from visited flowers and that, following injection in individuals belonging to the pollinator species Apis mellifera, it is able to establish an active infection, as indicated by the presence of replicating virus in the head of the injected bees. We also provide the first indication that the pollinator species Osmia cornuta is susceptible to DWV infection.

Genome sequence heterogeneity of Lake Sinai Virus found in honey bees and Orf1/RdRP-based polymorphisms in a single host

“…It implies that horizontal transmission of LSV can occur via infected bees, via the vectoring mite or via contaminated pollen. Although we do not provide causal evidence of transmission, cross-species transmission of honey bee viruses and subsequent infection has previously been experimentally demonstrated (Furst et al, 2014;Mazzei et al, 2014;Singh et al, 2010).…”

“…Moreover, the demonstration of virus replication in the solitary bee O. cornuta suggests that LSV is a multi-host virus, akin to other honey bee viruses such as DWV and IAPV. This solitary bee is also susceptible to DWV infection (Mazzei et al, 2014), but replication of these viruses is demonstrated in several pollinators (Levitt et al, 2013;Li et al, 2011;Zhang et al, 2012). Even clinical symptoms of an overt DWV infection, such as crippled wings, have been observed in bumble bees (Genersch et al, 2006).…”

Evidence of Varroa-mediated deformed wing virus spillover in Hawaii

“…and viable DWV particles have been found in pollen (Mazzei et al, 2014;McArt et al, 2014;Singh, 2011). Both honey bees and C. smaragdula were found foraging on the same common garden herbs, crops, and ornamentals -such as Scaevola sericea (Naupaka) and Heliotropium foertherianum -on both Oahu and Maui (pers.…”

Impact of managed honey bee viruses on wild bees

“…host varroa mites that can vector DWV, it is assumed that bumble bees and other wild bee species acquire DWV though robbing of DWVinfected colonies of Western honey bees for honey or, more likely, by collection and ingestion of DWV with pollen or nectar from flowers that are also visited by DWV-infected Western honey bee workers [27 , 39,40]. Given this assumption, we highlight two issues that confound the interpretation of data on DWV prevalence in wild bee species in terms of impact on hosts.…”