A study on novel transmission routes of honey bee (Apis mellifera L.) viruses with a focus on the epidemiological role of wax comb

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Date
2022-11-30
Authors
Colwell, Megan
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Abstract

European honey bees (Apis mellifera L.) are an integral element of modern agriculture in Canada and worldwide. However, there have been increased winterlosses of honey bee colonies for more than a decade. These losses are due to multiple factors, and include damage from a near universal parasite, Varroa destructor Anderson and Trueman (Acari: Varroidae), and the negative effects of honey bee viruses, some of which are vectored by varroa mites. It is vital to understand honey bee virus transmission in order to mitigate damage caused by infections. There is a dearth of research into wax comb as a potential transmission route of honey bee viruses. This thesis concentrates on elucidating the epidemiology of waxborne viruses, in terms of direct interaction with immature and adult honey bees, varroa and a honey bee inquiline (Braula coeca Nitzsch; Diptera: Braulidae). I developed a method to detect viruses directly from wax, and used that to explore waxborne viruses, focusing on the most common viruses in Canada: black queen cell virus (BQCV), deformed wing virus (DWV), and Israeli acute paralysis virus (IAPV). I discovered bee viruses in B. coeca for the first time and showed levels were similar to those in varroa despite vastly different life histories and interactions with comb. My results show that viruses were on winterloss wax. A cage study showed that worker bees easily contaminated wax through contact by walking on comb, in proportion to their own infection levels. I demonstrated that viruses could aerosolize within an incubator, though airborne transmission between adults is unlikely. I determined that both storage time and e-beam irradiation were able to reduce waxborne viruses, but temperature had no effect. Moreover, 35 and 45 kGy irradiation were more effective at virus reduction than time alone. My key result is that worker virus levels were increased when reared on high virus inoculated wax in a large-scale field experiment. Surprisingly, viruses were higher in adults reared on irradiated versus control wax. In summation, I found that wax does play a role in honey bee virus epidemiology and that wax is a viable route of honey bee virus transmission.

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Honey bee, Virus transmission
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