News from Prof. David J. Evans, The University of Warwick
Most honeybee studies are conducted on pooled samples from colonies but this prevents detection of very significant differences in the response of individual bees. A BBSRC UK/US Partnering Award shared knowledge in this area and a technique brought back from the States is going to revolutionise approaches to investigating honeybee health. Prof. David J. Evans, reports on the impact of the Partnering Award.
A colony of honeybees (Apis mellifera) is a busy place, particularly in mid-summer when the population peaks, with up to 50,000 workers crammed into a ~50 cm3 box. The crowded conditions provide ideal conditions for transmission of viral, bacterial and fungal pathogens during larval feeding. They also benefit the ectoparasitic mite Varroa destructor which infests the majority of colonies worldwide and acts as a vector for many honeybee viruses whilst feeding on haemolymph (blood).
Of particular concern is deformed wing virus (DWV), high levels of which reduces worker bee lifespan and can cause developmental defects in individual pupae.
Classic symptoms of abdominal stunting and wing deformities.
Image: Prof. David J. Evans
Unless beekeepers bi-annually apply miticides that reduce Varroa numbers, high levels of DWV build up in the colony and significantly increase overwintering losses. In long winters, like 2012/13, these losses can be greater than 50%.
Our research investigates the three-way interaction of the honeybee, DWV and the Varroa mite. We are interested in virus and mite-induced pathogenesis, the evolution of pathogenic variants of DWV and mechanisms to control virus proliferation. Using systems approaches we have investigated changes in the host transcriptome upon mite infestation and virus infection and have studied viral diversity and selection of pathogenic recombinant forms of DWV.
Although we now have an excellent insight into how Varroa contributes to DWV pathogenesis, we need to test these ideas using RNAi-based gene knockdown studies and virus challenge. Unsurprisingly this is almost impossible to do in a controlled manner within a full colony.
Jess Fannon.
Image: The University of Warwick
At a meeting of USA/UK honeybee researchers (funded by a BBSRC Partnering Award to Drs. Giles Budge, National Bee Unit, and Keith Delaplane, University of Georgia) we established a collaboration with Dr. Kate Aronstein of the USDA ARS Honeybee Breeding, Genetics and Physiology Research laboratory in Baton Rouge, Louisiana. This resulted in Jess Fannon, a research technician from the University of Warwick, visiting Baton Rouge in early 2013 to learn new methods necessary to maintain honeybee larvae in vitro.
Two to three day old larvae are harvested from a colony and fed an artificial diet under carefully controlled environmental conditions.
Larvae in controlled conditions.
Over a 15-18 day period the larvae grow, pupate and - if maintained long enough - emerge as adult bees. Controlled larval feeding 2-3 times a day allows oral delivery of bacteria expressing RNAi for studies investigating the consequences of, for example, immune system gene suppression. Similarly, DWV can be delivered in larval food, or, by injection of pupae, we can recapitulate the feeding activity of the Varroa mite. Raising larvae and pupae in vitro allows us to conduct dose response studies to test antiviral therapies and enables statistically robust analysis of results… all without any risk of being stung!
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