Effect of Varroa mite viral diseases on the honeybee (Apis mellifera) recognition system

AIMS The principle aim of this studentship is to investigate the effect of viral diseases on honeybee recognition systems and how these are exploited by the ecto-parasitic Varroa mite. Specifically the studentship aims to (1) understand how Varroa mites are able avoid detection by their honeybee hosts; (2) to investigate the interactions between, viral diseases, honeybee recognition cues and mite feeding behaviour. BACKGROUND Honeybees (Apis mellifera) are essential pollinators that contribute over £200 million p.a. to UK agriculture. The ectoparasitic mite Varroa destructor continues to represents the most significant risk to sustainable UK honeybee populations. In addition to the stress caused by Varroa feeding on honeybee haemolymph, the mites are known to transmit several honeybee viruses including Deformed wing virus (DWV) and Slow paralysis virus (SPV). Varroa operate within honeybee colonies, which are chemically complex environments. Despite strong colony recognition cues in honeybees, Varroa mites appear to be able to evade detection by mimicking the chemical recognition signals of the hosts they are feeding on although how this is achieved is not understood. Such chemical mimicry has to be very flexible as mites may often move between colonies, each with its own con-specific odour. The critical question as to whether the mites simply acquire the hydrocarbons from their hosts or synthesize them has never been resolved. This will be studied by comparing internal and external CHC profiles as well as the speed of change when challenged with different hosts e.g. bumblebees that have very different chemical profiles. The other key aspect of the Varroa story is that parasitised honeybees are known to exhibit an altered CHC profile compared to healthy bees, demonstrating the possibility that altered external chemistry is a response to stress, parasitism, or viral infection. This chemical information may be used by both the mites and honeybees to alter their respective behaviour. For example, parasitized bumblebees behave differently to healthy individuals, whereas aphids seek out virus infected plant material. We have a unprecedented opportunity to study this aspect in great detail since for the first time we have the knowledge and detection methods at Sheffield to link the chemical profiles of healthy bees and those infected with viral diseases which can both quantified and qualified at CSL. The ability of Varroa to transmit or activate honeybee viruses is the first step that ultimately leads to the death of the colony. It is possible that the strong correlation between Varroa and some viruses, like DWV, is enhanced by preferential feeding on virus-infected bees. Likewise, it is known that sap from diseased plants can be more nutrient rich than healthy plants and favoured by some parasites. Such a discovery of the chemical signals between honeybees and their pathogens would be key to understanding the current and future evolution and interactions of virus, host and ecto-parasites. In addition, identification of the key chemical signals involved in such a relationship could lead to novel, non-lethal methods for disease detection in honeybee colonies, which would be of great benefit to the beekeepers that are the key stakeholders.