Uncovering spatial relationships between honey bee (Apis mellifera) colonies and Varroa destructor in Maryland

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Stephen Todd Jr. and Stephanie R. Rogers, Geosciences, Auburn University, Auburn, AL, Geoffrey R. Williams, Entomology and Plant Pathology, Auburn University, Auburn, AL

Background/Question/Methods
Western honey bee (Apis mellifera) colonies have experienced increased rates of mortality in the Northern Hemisphere for the past decade. Factors that contribute to this increased mortality include beekeeper management practices, weather and climate, pesticide use, land-use change, and parasites, including Varroa destructor. Varroa destructor are one of the main threats to honey bee colonies, but their spatial variability is poorly understood, leading to improper management strategies by beekeepers, which contribute to elevated rates of colony loss. Based on the first law of geography, where everything is related, but nearer phenomena are more related than those which are farther apart, I predict that the distribution of V. destructor are spatially clustered, that is, infestation levels are more similar among colonies that are closer together than those which are farther apart. Thus, do V. destructor exhibit spatial clustering across space and time, and what is the appropriate neighborhood size and scale in understanding V. destructor spatial clustering? To answer these research questions, data were obtained from the Bee Informed Partnership (BIP) Sentinel Apiary program, which included 1,271 colony samples from Maryland and the surrounding region spanning May through October 2015. The dataset contains geographic coordinates for colonies and V. destructor population levels represented as number of mites per 100 bees. The Spatial Autocorrelation (Global Moran’s I) tool in ArcGIS Pro 2.6 was used at the automatically generated optimal distance band (58 m) and a manual distance band (1 km) to measure the presence and intensity of spatial clustering in V. destructor populations. A positive Moran’s I index indicates that clustering is present, while z-score and p-value report the significance of the Moran’s I index.
Results/Conclusions
Results showed that V. destructor populations were spatially clustered in all months except June using the optimal distance band of 58 m. When using the 1 km distance band, all six months were spatially clustered for V. destructor infestation levels. This means that infestation levels are more similar among colonies that are closer together than those that are farther apart, indicating that more intense monitoring and management is required for colonies that neighbor highly infested colonies. Our next steps include expanding the survey area and timeframe so that comparisons between regions across multiple years can be analyzed.