Predictive-associative assessment of Varroa destructor and Tropilaelaps clareae infestations with hive and environmental determinants in Apis mellifera colonies

The present study examined the population dynamics of Varroa destructor and Tropilaelaps clareae in Apis mellifera colonies and their relationships with weather and colony parameters. A year-round infestation was assessed through four indices, mite fall (MF), sealed brood infestation (SBI), unsealed brood infestation (UBI), and worker bee infestation (WBI), in singly and co-infested colonies. V. destructor was present throughout the year, while T. clareae showed a more seasonal pattern, with peak activity during the warmer months. In colonies where both mites occurred together, each species exhibited distinct periods of higher abundance. Overall, fluctuations in brood and worker bee infestations closely followed the temporal trends of mite fall, with statistically significant variations observed across the observation period. Correlation analysis revealed that both mite species showed strong positive associations with brood area and frame strength, while relative humidity exhibited a significant negative relationship with most infestation indices. In contrast, rainfall negatively affected V. destructor brood infestation under co-infestation conditions. Multiple regression models identified soil temperature, brood area, and frame strength as the major predictors of mite fall, collectively explaining 70.6% and 78.4% of the variation in V. destructor and T. clareae mite fall, respectively, under single infestations. The predictive power decreased under co-infestation, with R² values of 0.503 for V. destructor and 0.743 for T. clareae. Principal Component Analysis (PCA) further supported these findings, indicating that brood area, frame strength, and soil temperature were the primary drivers of mite buildup, while rainfall and relative humidity acted as constraining factors. The ordination separated singly infested colonies from co-infested ones, highlighting the dominant influence of colony strength and brood activity on mite dynamics in A. mellifera colonies.