Selection of Apis mellifera workers by the parasitic mite Varroa destructor using host cuticular hydrocarbons

Abstract

The parasitic mite, Varroa destructor, is the most important threat for apiculture in most bee-keeping areas of the world. The mite is carried to the bee brood cell, where it reproduces, by a nurse bee; therefore the selection of the bee stage by the parasite could influence its reproductive success. This study investigates the role of the cuticular hydrocarbons of the European honeybee (Apis mellifera) in host-selection by the mite. Preliminary laboratory bioassays confirmed the preference of the varroa mite for nurse bees over pollen foragers. GC-MS analysis of nurse and pollen bees revealed differences in the cuticular hydrocarbons of the two stages; in particular, it appeared that pollen bees have more (Z)-8-heptadecene than nurse bees. Laboratory experiments showed that treatment of nurse bees with 100 ng of the pure compound makes them repellent to the varroa mite. These results suggest that the mite can exploit the differences in the cuticular composition of its host for a refined selection that allows it to reach a brood cell and start reproduction. The biological activity of the alkene encourages further investigations for the development of novel control techniques based on this compound.

High Varroa mite abundance influences chemical profiles of worker bees and mite–host preferences

“…These results are consistent with those obtained when comparing the total time spent by the mite on the two bees (Z=-2.5, P=0.008; Z=-0.32, ns; Z=-0.55, ns, respectively). As the mite preference for bees performing different tasks is driven by a specific blend of cuticular hydrocarbons (CHCs) covering the body surface of nurses and foragers (Del Piccolo et al, 2010), we explored whether the chemical signature of nurses and foragers differed among individuals coming from colonies with different mite abundance. CHCs of nurses and foragers collected from three colonies with different mite abundance (no mites, 0.13 and 0.45) were extracted and analysed by gas chromatography coupled with mass spectrometry (GC-MS).…”

“…We tested this hypothesis by presenting phoretic mites (N=309) collected from eight hives (five out of the seven abovementioned colonies and three additional ones) with a binary choice between homocolonial and heterocolonial foragers. As mites are able to recognize different hydrocarbon blends on the bee cuticle (Del Piccolo et al, 2010), they may discriminate differences in the chemical signature among foragers belonging to different colonies. We found that 224 choosy mites [65 mites (21%) did not make any choice], regardless of the mite abundance of the colony, did not show nestmate host recognition ability (G=4.84, d.f.=2, ns) or, at least, they did not express it in our experimental setup (Fig.…”

“…After leaving the cell, the mite enters the phoretic phase by staying on an adult host for a few days or weeks before entering a new brood cell for the next cycle of reproduction. Previous research (Del Piccolo et al, 2010) has shown that mites, once emerged from the cells, prefer to ride on nurses, distinguishing them from foragers via chemical cues; the nurses will most likely bring the mites in contact with brood susceptible to infestation, a behaviour favouring parasite reproduction. However, this preference is advantageous for mites only when they seek another brood cell in the same colony in which to reproduce.…”

Standard methods for chemical ecology research inApis mellifera

“…(Carlson and Bolton, 1984), nestmate recognition (Dani et al, 2005) and elucidation of host-parasite relationships (Rickli et al, 1994;Salvy et al, 2001;Del Piccolo et al, 2010). (Blomquist et al, 1980;Francis et al, 1985;Francis et al, 1989;Carlson et al, 1989).…”

The chemical ecology of host-parasite interaction as a target of Varroa destructor control agents

“…Brood food contains a volatile compound, 2-hydroxyhexanoic acid 24 (enantiomer not known), that is attractive to phoretic Varroa females (Nazzi et al 2004). Finally, foragers appear to have higher titers of (Z )-8-heptadecene 25 in their cuticular hydrocarbon blend than nurses, and this compound has been also shown to deter Varroa females (Piccolo et al 2010).…”