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Many studies have described the positive effect of food restriction on aging and longevity in rodents as well as a genetic pathway activated in response to starvation in nematodes and mice. This genetic pathway may be conserved across phyla and some authors are convinced that these studies could help delay aging, particularly human aging. I suggest that these studies are analyzing a rescue program used to resist starvation but not active in ad libitum-fed animals. Whether these studies provide an increased understanding and ability to delay aging under the usual living conditions of animals and humans is unclear. The study of hormesis is proposed as a way of studying aging under normal living conditions, because ad libitum-fed animals subjected to mild stresses can live slightly longer than control animals and display increased resistance to strong stresses. It would be of interest to study, in animals subjected to a mild stress inducing hormesis, the response to non-lethal stresses rather than lethal ones, because elderly people are more often confronted by such non-lethal stresses (e.g., temperature drop in winter) than by lethal ones.

A task was designed to teach individual flies to avoid a lighted area after they had displayed an initial preference for it. The flies walked in a T-maze and chose between a lighted and a darkened alley leading, respectively, to a lighted and a darkened vial. Flies that were photopositive on a first trial were subjected to an aversive stimulus (a filter paper inserted into the lighted vial and wetted with a quinine solution), and they performed 16 training trials; they learned to avoid the lighted vial. The flies trained with water instead of quinine in the lighted vial still display avoidance of the lighted vial, but to a lesser extent. The flies trained with a dry filter paper in the lighted vial did not show any increase in avoidance during training. Like the flies trained with no quinine at all, those trained to avoid the lighted vial under a partial reinforcement condition (one half of the trials with quinine, the other half with a dry vial) did not master the task. Finally, removal of the quinine after an avoidance acquisition criterion was reached resulted in an extinction process.

Previous studies have shown that Drosophila melanogaster males live longer if exposed to hypergravity at young age. Similarly, thermotolerance and climbing activity in old age are enhanced and it has been hypothesized that the 70 kDa inducible heat-shock protein (hsp70) may play a role in some of these effects. In this article, longevity, thermotolerance and climbing activity were studied in transgenic flies (OE+ strain) overexpressing hsp70 and in control flies harboring the transfection vector at the same chromosomal location but no extra-copies of the hsp70 gene (OE- strain). No positive effect from exposure to hypergravity at a young age was observed for longevity and climbing activity. Thermotolerance was increased by hypergravity but to the same extent in OE+ and OE- strains. Since no positive effect from hypergravity exposure or similar effects were observed in the two strains, it may be concluded that overexpression of hsp70 does not provide an advantage to flies subjected to a mild stress and that it may not be of any help during aging.