Feeding behavior and distribution of Varroa destructor on adult bees of Apis mellifera

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Varroa destructor is a competent vector of honey bee viruses and the leading cause of colony losses worldwide. Much about its feeding behavior and distribution on adult bees remains unknown. This work shows that Varroa are promiscuous feeders of adult bees, actively switching from one host to another. Laboratory trials showed there is a large heterogeneity in the host switching rate with some Varroa switching infrequently while others switched at high rates. The consequences of Varroa feeding on adult bees is largely unknown because adult feeding has largely been overlooked. This work shows that there is a high relative risk of death from Varroa feedings. Adult workers die quickly without developing high levels of infection after being fed upon by an infectious Varroa, and confer lower risk to their non-parasitized nestmates than counterparts which were nestmates to longer lived parasitized bees. Further experiments showed communicable routes of virus transmission may explain these findings. Trophallaxis between adult workers allowed for the movement of the pathogen to naïve nestmates. These nestmates act as an infectious reservoir to naïve Varroa showing communicable transmission between hosts can influence the acquisition and subsequent vectoring of the same pathogen by the vector. Another social behavior, cannibalization, was shown to have the same influence on Varroa vectoring. Varroa were also shown to be susceptible to viral acquisition through shared feedings on adult bee and brood hosts. Naïve Varroa readily acquired and then transmitted deformed wing virus when sharing the same host with an infectious Varroa. Collectively this work exemplifies how host social behavior and Varroa-Varroa transmission routes can increase the risk of vectors becoming infectious. Varroa feedings and virus transmission on adult workers cannot describe one of the most glaring features of Varroa infestations. For a portion of the year Varroa aggregate predominantly on adult drones, largely ignoring the worker cohort. Parasite burden only shifts onto workers when drone production ceases.