Exploring virus-virus interactions in the honey bee parasite Varroa destructor

The Western honey bee (Apis mellifera Linnaeus, 1761) is an ecologically and economically valuable pollinator, contributing an estimated USD 235-577 billion (NZD 411–1,011 billion) annually to global agriculture through pollination services. The increase in food demand coupled with anthropogenic-induced environmental changes that include habitat fragmentation, pesticide exposure, and climate change have placed immense strain on honey bee colonies. Modern apicultural practices often necessitate high-density apiaries and frequent hive transportation, creating overcrowded conditions that make bees significantly more susceptible to parasites and diseases. The ectoparasite Varroa destructor (Anderson & Trueman, 2000) is a globally regarded pervasive threat to honey bees. Beyond the physical damage honey bee pupae withstand from mite feeding, the mites also serve as vectors for various RNA viruses that threaten the health of honey bees. Among these vectored pathogens, deformed wing virus (DWV) is the most prevalent and poses an economically significant threat. The variant deformed wing virus type A (DWV-A) is the most widespread in New Zealand and causes symptoms such as wing deformities, impaired foraging abilities, decreased reproductive success, reduced honey production, and increased colony mortality. Varroa destructor also harbours the recently discovered Varroa destructor virus-2 (VDV-2), which selectively replicates in mites and shows negative associations with DWV in field samples, suggesting potential competitive interactions. The potential interactions between DWV-A and VDV-2 were investigated through controlled inoculation via an artificial diet and immersion in DWV targeting double stranded RNA (dsRNA). Our findings suggest there is no direct interaction between these viruses under the experimental conditions tested. However, low levels of VDV-2 were detected, highlighting the methodological challenges and underscoring the need for further investigation to truly determine the ecological significance of VDV-2.