NO TWO WAXES ARE THE SAME

Distinguishing friend from foe is as important for insects as it is for any other creature. You need to know when you're on someone else's territory and when an impostor is threatening. Many insects depend on their sense of smell to identify nest mates, and bees are no different; they recognise wax scents picked up by bees from their own nest, explains Robert Buchwald. However,wax's role in communication was probably a secondary evolutionary factor after its other main purpose: construction, where bees sculpt wax into nests and exquisite hexagonal combs to store honey and nurture larvae. Knowing that bees can distinguish wax scents carried by bees from other nests, Buchwald and Michael Breed wondered whether these subtle differences in composition also impacted on the material's structural properties. They decided to investigate waxes from several species to find out whether they were mechanically indistinguishable, or each had been honed to suit the structural needs of each species' nests (p. 3984). The pair teamed up with mechanical engineer Alan Greenberg to measure several waxes' mechanical properties, but first they needed nests to test.Buchwald explains that getting hold of Apis mellifera nests was straightforward; he simply visited the apiary at the University of Colorado at Boulder. However, tracking down the more exotic Apis species was much trickier. Fortunately, the team established a strong collaboration with Canadian scientist Gard Otis, who supplied them with nests during his field work in Asia, despite running the constant gauntlet of bee stings.Melting down the nests, Buchwald and Greenberg cast each species' wax into a cylinder shape to remove the nests' architectural differences, before compressing the wax to test its structural properties. But working with the soft wax samples was very different from the construction materials that Greenberg usually studied; the team had to find the most sensitive stress detector for the compression system that they used to calculate each waxe's mechanical strength and stiffness.Analysing the results, the team realised that Apis dorsata's wax was by far the strongest and stiffest, while Apis andreniformis's was the weakest and softest. Each species' wax was mechanically unique and unlike the other three's.Buchwald suspects that the bees' nesting habits could account for the mechanical differences. He explains that Apis dorsata's colossal nests not only have to support the greatest weight, but also must withstand knocks and high winds in their exposed locations, suspended from tree branches high above the forest canopy. Meanwhile, Apis cerana and Apis mellifera build their nest combs in protected cavities, such as dead trees, which seems to have resulted in the insects evolving intermediate-strength waxes. However, Buchwald was most surprised by Apis andreniformis's wax. He explains that, like Apis dorsata,andreniformis hangs its nests from tree branches. But andreniformis nests are much smaller than hefty dorsata's and are located in the relative protection of the forest's lower reaches,hanging from springy branches that protect the nests from mechanical shocks. Buchwald suspects that these differences in lifestyle have allowed andreniformis to evolve softer wax than dorsata's robust blend.

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