Multiple function of pteridines in Drosophila: The fluorescence of the ejaculatory bulb in Drosophila melanogaster

It is demonstrated that the strong fluorescence of the ejaculatory bulb of Drosophila melanogaster males is caused by the presence of pteridines. The pteridine composition in the bulb is affected by the mutations ry² and ma-l^F1 in which isoxanthopterin has also been detected. Our results show that the bulbs of wild-type and white-eyed mutant males possess the same pteridines. Some data suggest that the bulbal pteridines originate from the testis region. Partly on the basis of former histochemical findings it is suggested that in the bulbal cavity the pH is high favouring the fluorescent dihydro-states of the pteridines present. All these and additional literature data on the ejaculatory bulb are discussed in connection with various biological processes. Some internal larval structures in which pteridines play or might play a functional role were found to present autofluorescence.