A cold stress applied at various ages can increase resistance to heat and fungal infection in aged Drosophila melanogaster flies.

A cold stress applied to young flies can have positive effects on longevity, behavioral aging, and resistance to heat and infection. However, the same mild stress, if applied at older ages, i.e. in frailer flies, could be a strong stress with negative effects. Cold stress was applied at various ages (weeks 1-2, 2-3, 3-4, and 4-5) and its effect on longevity and on resistance at 6 weeks of age to heat or fungal infection was observed. In males, the cold stress had positive effects on longevity and resistance to infection, except when applied at the oldest age. No positive effect on longevity or resistance to infection was detected in cold-stressed females, as already observed in previous experiments using a cold stress at young age only. By contrast, cold stress applied at various ages increased resistance to heat in both sexes. Therefore, a mild stress can have positive effects on longevity and resistance to strong stresses not only when used at a young age, but also at older ages.