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Just quickly for now without commentary:
Totally cool paper in the last Science:

S. Libert, J. Zwiener, X. Chu, W. VanVoorhies, G. Roman, and S.D.Pletcher

Regulation of Drosophila lifespan by olfaction and food-derived odors:

Smell is an ancient sensory system present in organisms from bacteria to humans. In the nematode Caeonorhabditis elegans, gustatory and olfactory neurons regulate aging and longevity. Using the fruit fly, Drosophila melanogaster, we show that exposure to nutrient-derived odorants can modulate lifespan and partially reverse the longevity-extending effects of dietary restriction. Furthermore, mutation of odorant receptor Or83b results in severe olfactory defects, alters adult metabolism, enhances stress resistance, and extends lifespan. Our findings indicate that olfaction affects adult physiology and aging in Drosophila possibly through perceived availability of nutritional resources and that olfactory regulation of lifespan is evolutionarily conserved.

From Nature News:

Eating less can lengthen an animal’s life. But now it seems that — for flies at least — they don’t have to actually cut down on the calories to benefit. Fruitflies can boost their lifespan just by not smelling their food.

The result suggests that flies might use their sense of smell — as well as the actual consumption of food — to help determine how rich their environment is, and how they should go about distributing their energy resources.

From flies and worms to rats and mice, animals fed on restricted diets generally live longer than those given abundant food. No one is sure exactly why this is. One theory is that when times are tough and there is little food about, animals channel more of their resources into maintaining their everyday body function, at the expense of putting energy into reproducing. That can extend lifespan.

Scott Pletcher of the Baylor College of Medicine in Houston, Texas, wanted to find out what governs this decision. Smell, he thought, might be one determinant. “We wanted to see whether we could use odor to trick the flies into thinking the environment was more nutrient-rich than it actually was,” says Pletcher.

Normally, cutting a lab fly’s usual food intake in half lengthens its lifespan by about 20%, from 41 to 50 days. But exposing hungry flies to the scrumptious smell of yeast, a favourite food, took away some of this benefit, the team found. “About one-third of the beneficial effects on lifespan are lost,” says Pletcher.

The yeasty odor had no effect on the lifespan of fully fed flies.

And one of th authors gives additional explanation on the Nature News blog:

We measured the reproduction (fecundity) of OR83b flies and controls. Data is in fig 4a, there is no significant difference, when flies are fully fed. We did not present the data but the quality of eggs (percent that hatches, SL observation) seems to be unaffected. Even if flies would perform worser under stress (lay less eggs under stress for example) it is unlikely to be the cause of longevity, since during the longevity experiment, flies are not stressed in anyway.

It is possibe that the dfference is small, so that we can not detect it, but in this case it is unlikly to be the cause of 56% longevity extension.

Additionally, the work from Tatars lab for at least in some systems, uncoupled reproduction from longevity.