When the time came for chemical ecologist Walter Leal to test whether humans make a natural odor that attracts mosquitoes, Leal himself was the first to volunteer. ‘I measured my own levels,’ Leal said. ‘I thought I would set a good example. If you do it first, then others won’t be scared.’ In truth, there was little if any reason to be frightened. The scientists were looking only for the substance itself, not trying to find out whether the compound would lure the insects into a blood meal. And they found it - nonanal, a substance made by humans and birds that creates a powerful scent that Culex mosquitoes find irresistible. Leal only had to roll up his sleeve. His colleagues laid a syringe-like instrument next to his skin, and then wrapped his arm in aluminum foil to keep the environment confined. After an hour, the tip of the syringe was injected into a special machine to see if it contained nonanal and, if so, how much his body had produced. Plenty, as it turned out. ‘It’s there. I have lots of it,’ he said. ‘I think I released 20 nanograms in an […]