Varroa destructor Mites Can Nimbly Climb from Flowers onto Foraging Honey Bees

Abstract

Varroa destructor, the introduced parasite of European honey bees associated with massive colony deaths, spreads readily through populations of honey bee colonies, both managed colonies living crowded together in apiaries and wild colonies living widely dispersed in natural settings. Mites are hypothesized to spread between most managed colonies via phoretically riding forager bees when they engage in robbing colonies or they drift between hives. However, widely spaced wild colonies show Varroa infestation despite limited opportunities for robbing and little or no drifting of bees between colonies. Both wild and managed colonies may also exchange mites via another mechanism that has received remarkably little attention or study: floral transmission. The present study tested the ability of mites to infest foragers at feeders or flowers. We show that Varroa destructor mites are highly capable of phoretically infesting foraging honey bees, detail the mechanisms and maneuvers by which they do so, and describe mite behaviors post-infestation.

Fig 1. Experimental setup to monitor mite behavior towards foraging honey bees.

To see whether mites fell off bees after climbing onto them, the top of the cup holding the focal flower was covered in white paper, as was the stool on which the cup sat. The entire apparatus was underlain by a 1m by 2m sheet of white cloth.

Fig 2. The number of bee-seconds before a honey bee forager was infested by the focal mite.

Boxplots shown for each of the three species used, and pooled data from all three species. Boxes span the first through third quartiles, and whiskers span the range of non-outlier values.

Fig 3. Sites of initial contact between foragers and mites (n = 71), and the sites at which mites came to rest (n = 58).

Numbers in parentheses denote the number of mites observed interacting with each host body part. Data are pooled from feeder and flower observations. A: Any part of the ventral abdomen; B: Legs, above the tarsal claw; C: Ventral or lateral thorax or proximal surface of legs; D: Ventral surface of head; E: Proboscis; F: Antenna. T: Anterior dorsolateral abdomen, 1^st segment; U: Intertagmal region between thorax and abdomen (“waist”); V: Central dorsal thorax; W: Intertagmal region between head and thorax (“neck”); X: Ventral abdomen; Y: Ventral thorax; Z: Dorsal trochanter or femur. The asterisk refers to the space between the 3^rd and 4^th tergites: the most common location for Varroa found on hive bees in past studies.