Use of electropenetrography (EPG) and histology to understand the feeding behaviors and biomechanics of Varroa destructor mites on honey bee pupae

The parasitic mite, Varroa destructor, is an obligate ectoparasite of honey bees.  AC-DC Electropenetrography (EPG) recording technique was used to understand the feeding behavior and biomechanics of female Varroa mites on pupae of the honeybee (Apis mellifera). EPG signals characteristic of arthropod suction feeding (ingestion) were identified for mites that fed on pupae during overnight recordings. Ingestion by these mites was confirmed afterwards by observing internally fluorescent microbeads previously injected into their hosts. Micrographs of internal ingestion apparatus illustrate a pharyngeal lumen surrounded by alternating dilator and constrictor muscles. Inspection of EPG signals showed the mite pharyngeal pump operates at a mean repetition rate of 4.5 cycles/s to ingest host fluids. Separate feeding events observed for mites numbered between 23 and 33 over approximately 16 h of recording, with each event lasting ~10 s. Feeding events were each separated by ~2 min. Consecutive feeding events separated by either locomotion or prolonged periods of quiescence were grouped into feeding bouts, which ranged in number from one to six. EPG data revealed that feeding events were prolonged for mites having lower pharyngeal pump frequencies, and mites having prolonged feeding events went unfed for significantly more time between feeding events. These results suggest that mites may adjust behaviors to meet limitations of their feeding apparatus to acquire similar amounts of food. The EPG data reported here help to provide a more robust view of Varroa mite feeding than those previously reported and also allow comparisons with those of the blood-feeding ticks.