Perhaps the old wax is impregnated with semiochemicals from the generations of brood?
Studies of Varroa destructor orientation to honey bees were undertaken to isolate discrete chemical compounds that elicit host-finding activity. Petri dish bioassays were used to study cues that evoked invasion behaviour into simulated brood cells and a Y-tube olfactometer was used to evaluate varroa orientation to olfactory volatiles. In Petri dish bioassays, mites were highly attracted to live L5 worker larvae and to live and freshly freeze-killed nurse bees. Olfactometer bioassays indicated olfactory orientation to the same type of hosts, however mites were not attracted to the odour produced by live pollen foragers. The odour of forager hexane extracts also interfered with the ability of mites to localize and infest a restrained nurse bee host. Varroa mites oriented to the odour produced by newly emerged bees (<16 h old) when choosing against a clean airstream, however in choices between the odours of newly emerged workers and nurses, mites readily oriented to nurses when newly emerged workers were <3 h old. The odour produced by newly emerged workers 18-20 h of age was equally as attractive to mites as that of nurse bees, suggesting a changing profile of volatiles is produced as newly emerged workers age. Through fractionation and isolation of active components of nurse bee-derived solvent washes, two honey bee Nasonov pheromone components, geraniol and nerolic acid, were shown to confuse mite orientation. We suggest that V. destructor may detect relative concentrations of these compounds in order to discriminate between adult bee hosts, and preferentially parasitize nurse bees over older workers in honey bee colonies. The volatile profile of newly emerged worker bees also may serve as an initial stimulus for mites to disperse before being guided by allomonal cues produced by older workers to locate nurses. Fatty acid esters, previously identified as putative kairomones for varroa, proved to be inactive in both types of bioassays.
Exp Appl Acarol. 2005;37(1-2):1-26.
Semiochemicals influencing the host-finding behaviour of Varroa destructor.
Pernal SF, Baird DS, Birmingham AL, Higo HA, Slessor KN, Winston ML.
>
> Varroa destructor preferentially invades larger honey bee brood cells. Consequently, it was
> expected that brood in old combs with reduced-size cells would be less infested than the brood in new comb
> cells. An old brood comb was placed in each of eight Africanized honey bee colonies, along with a new,
> naturally constructed comb (without comb foundation). The mean percentage of brood cells infested with
> V. destructor was significantly higher in the old combs (22.6%), than in the new combs (9.75%), even
> though the inside width of the cells was significantly smaller in the old (4.58 mm) than in the new combs
> (4.85 mm). Within the range where there was an overlap in the width of brood cells between old and new
> combs, which was from 4.5 to 4.9 mm, the old comb cells were over four times more frequently infested
> with mites than were the new comb cells. Some factor other than cell size makes old brood comb cells much
> more attractive to V. destructor than newly constructed brood comb.
>
> Piccirillo, G. A., & De Jong, D. (2004). Old honey bee brood combs are more infested by the mite Varroa destructor than are new brood combs. Apidologie,35(4), 359-364.
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