DIETARY AMINO ACID AND NUCLEIC ACID IMBALANCE LEADING TO ALTERED TUMOUR FREQUENCY IN ADULT HOUSEFLY MUSCA DOMESTICA

Bioinduction of internal melanotic tumours and melanotic sclerosis in adult male and female houseflies was accomplished by elevating the l-phenylalanine content of a fully chemically defined diet beyond 1 per cent levels. A high frequency of tumour formation and sclerosis was dependent on the presence of eight essential l-amino acids in the diet: tryptophan, phenylalanine, leucine, isoleucine, valine, arginine, lysine, and threonine. Methionine was non-essential for tumour formation in males and intermediate in its position between essential and non-essential acids for female tumour formation. l-Histidine, essential for ovarian development, was non-essential for tumour formation. Tumour formation and sclerosis appeared to be related directly to the animal's ability to synthesize protein, presumably in the form of enzymes or other proteins required for melanin formation. Supplementing the tumour-inducing (TuI) diet with RNA (0·4%) was somewhat effective in reducing tumour frequency whereas DNA was without effect. Individual purine or pyrimidine bases reduced tumour frequency by as much as 90 per cent of controls. Ribose and deoxyribose nucleosides and nucleotides were without significant effect with two important exceptions. Guanosine and guanylic acid greatly reduced tumour frequency in females but not males. Thymidine and thymidylic acid had the reverse effect. Several time-dependent features of tumorigenesis were observed: tumour formation was confined to about a 24 hr period commencing 2·5 days after emergence. All animals developing tumours died; thereafter survivors were highly resistant to tumorigenesis. Systematically ageing houseflies on a sucrose diet before feeding the TuI diet resulted in a dramatic decline in tumour frequency in females. Similarly aged males showed a high mortality rate of uncertain cause. It is suggested that tumorigenesis in adult houseflies may serve as a useful model system for the study of several aspects of insect physiology, notably nutritional balance and imbalance, mechanisms controlling the tyrosine/tyrosinase system in the blood and tissues of insects, factors influencing the darkening of the adult cuticle, ageing, pathology, and population control of insects by nutritional methods. © 1968.