Parasitic dynamics of Varroa destructor and Nosema spp. and their associations with the health of honey bee (Apis mellifera) colonies in small-scale apiaries in Argentina

Abstract

Global apiculture faces significant health challenges due to parasites such as the mite Varroa destructor and microsporidia of the genus Nosema, which can severely affect the Apis mellifera colony health and honey production. This study evaluated the dynamics of these parasites and their association with colony health in small-scale beekeeping systems. A longitudinal study was conducted in nine apiaries, with five colonies per apiary monitored over the course of an annual cycle, including two samplings during both productive and non-productive seasons. Parasite prevalence and mean abundance were assessed alongside health indicators such as brood proportions and pollen and honey reserves. Results indicated that V. destructor reached peak abundance during the productive season (p < 0.001), coinciding with colony expansion, whereas Nosema spp. peaked at the beginning of the non-productive season (p < 0.001) following acaricide treatment. These patterns suggest a competitive or opportunistic interaction wherein Varroa acts as the dominant parasite, modulating Nosema spp. infection dynamics. Additionally, eight colonies died during the study (17.7%); higher parasite loads in non-survivors suggest a potential contribution to colony losses, although causal mechanisms remain to be elucidated. During the productive season, higher open brood proportions were associated with Varroa-free colonies (p = 0.048), while mite presence correlated with increased pollen stores (p = 0.022). These findings highlight functional health indicators that are useful for monitoring parasitic dynamics in small-scale production systems and underscore the importance of integrated management strategies and long-term research to better understand parasite-host interactions in small-scale apiculture.