Insect Preservation Methods Allow Quantification of Dispersing Microorganisms by Scanning Electron Microscopy

Abstract Insects may act as dispersal vectors for microbes where microbes can temporarily adhere to insect exoskeletons. Microbes carried by honey bees (Apis mellifera) may experience a range of dispersal outcomes, from successful colonisation of a new habitat to predation by grooming bees, partly depending on their location on the bee exoskeleton and the carried population size. I tested four methods for handling collected bees, and examined the bees in a scanning electron microscope, imaging and counting microbial cells attached to tarsal claws. Freeze-dried bees carried more microbial cells than bees that were pinned and air-dried, preserved in 96% ethanol then dried by CO2 critical-point drying, or bees washed with potassium phosphate then preserved in 96% ethanol, but some microbes were found on bees from every treatment. The similarity in microbial passengers found between air-dried and ethanol-preserved bees suggests that examination by electron microscopy could be used to address questions regarding microbial dispersal by pollinators already present in collections associated with other pollination research.