It doesn't take much to begin feeling dehydrated. Miss a couple of drinks on a hot day and you'll soon experience the effects. But tiny insects are particularly at risk, thanks to their relatively large surface area – compared with their tiny body mass – through which they can lose fluid. For protection, they are encased in a tough exoskeleton, which can help to reduce water loss. In addition, their surface is smeared with wax, which could also minimise the amount of water they lose. However, no one had ever checked whether this layer of wax actually offers protection from dehydration or even alters the amount of dehydration that an insect can withstand. To find out whether the wax coating provides waterproofing, Kamar Nayal, Joshua Krupp, Osama Abdalla and Joel Levine from the University of Toronto at Mississauga, Canada, painstakingly engineered special fruit flies (Drosophila melanogaster) that had lost the wax-producing cells and so were unable to produce the waxy coating. Then they tested how well the wax-less flies fared in dry desert-like air.
It turned out that the wax-less flies were able to withstand the same amount of dehydration as the flies that were still able to produce the wax, so coating the surface of their exoskeleton with wax hadn't altered their ability to survive dehydration. However, it became clear that the waxy coating reduced how quickly the flies dried out in desert-like air. The well-waxed flies generally withstood the dry air for 6–9 h, while the wax-less flies struggled to cope beyond 3–6 h. And when the team measured how quickly the wax-less flies lost water from their bodies, they found the females lost water 1.7 times faster than flies coated with wax, and the males dehydrated 1.4 times faster.
But what happened when the researchers provided the wax-less flies with a coating of the wax produced by normal flies? Would re-waxing protect the flies that were vulnerable to dehydration? Sure enough, the new wax coating did reduce the insects’ water loss by 200–300%. And when the team checked how well female wax-less flies survived dehydration after mating with waxy males, it turned out that the females coped better, suggesting that some of the male's wax is transferred to his mate, offering her some protection.
Fruit fly waxy coatings provide the insects with protection from dehydration and Levine and colleagues are keen to zero in on the precise chemicals in the waxy mixture that provide the majority of the waterproofing that keeps the insects well hydrated.
