Influence of photosensitizers and light on the life span of Drosophila.

The life span of adult Drosophila melanogaster fruit flies changed when they were fed two different photosensitizers. Methylene blue decreased the median life span by 49% when present in the food at a concentration of 0.001 M. Another photosensitizer, riboflavin, produced no changes in life span under the same conditions of a 12:12 h light/dark cycle at a daytime light intensity of 1000 lux. Flies exposed to constant darkness lived 43.2% longer than those exposed to constant light at a light intensity of 2000 lux. Under these conditions, riboflavin increased the life span of the flies exposed to constant light by as much as 25%. We conclude that riboflavin confers some degree of protection against the effects of constant light exposure. The completely different results obtained with riboflavin and methylene blue suggest a possible mechanism for photoageing involving photodynamic action mediated through the production of singlet oxygen.