Varroa destructor and Nosema sp seasonal dynamics in Apis mellifera colonies from temperate climate in Argentina

Abstract

The obligate ectoparasites Varroa destructor and Nosema sp affect honey bee Apis mellifera health and generate important colony losses. This paper describes and analyze information from sentinel units about varrosis and nosemosis regional distribution and prevalence level during three years, according to a surveillance program of EEA INTA Rafaela and INTA national beekeeping program. During the study, a total of 49 apiaries were monitored in four different zones of Santa Fe Province (North, South, Riverside and Central zone), which were visited at three moments every year: before autumn acaricide treatment, after the treatment and at the beginning of spring. Data about apiary management practices and samples for Varroa mites and Nosema were collected. We found high percentages of Varroa after treatment in South Zone during 2017 and in North Zone during 2018 and 2019. Our results suggested that, both region and control strategies impact on Varroa infestation level during the course of the year, being their relative importance depend on the moment when it is observed. In addition, seasonal trend of Varroa in response to bee dynamic population explained the absence of interaction between period and year factors. According to our study, a surveillance program by means of sentinel apiaries which identify the main spread period was effective in monitoring and remedying the level of both pathogens, so to ensure a healthy bee colony.