Leslie Vosshall from Rockefeller University studies the sense of smell in fruit flies. Drosophila larvae compare left and right olfactory inputs to find food sources. On a petri dish, these larvae find odor sources within about one minute. Genetically ablating olfactory receptor gene Or83b, renders the larvae anosmic. Then, one can re-insert one receptor at a time to see which components of the olfactory system are required for the chemotaxis. It turned out that a single receptor is sufficient for locating the odor source. In flies, you can genetically switch of smell on just one side of the animal and see what they do. These animals behave roughly in-between the completely anosmic animals and the flies with just one receptor, but on both sides of the brain (bilateral). Interestingly, when the left side was switched off, the animals did better than when the right side switched off. Are even fly larvae ("maggots") right-"handed"???
So if they are supposed to compare left and right input, but can do it even with only one input (albeit worse than with two), how do they do it? Apparently, all the bilateral input does is to decrease the noise in the detection of the odor gradient. Single receptors can still detect a gradient, but the accuracy is greatly reduced.
At the end, Leslie showed us some data on how important the sense of smell is for survival under conditions of limited resources. She did this by reducing the amount of food and spread it out on the petri dish and then let smelling and anosmic larvae compete for the food. Not surprisingly, smelling larvae survive, anosmic die. Similar results were presented for adult flies.