Studies on zinc toxicity in the larvae of the rice moth, Corcyra cephalonica St.

Zinc salts fed at relatively high concentrations in the diet have been known to produce deleterious effects. Sutton & Nelson (1938) found that 1 % of zinc as carbonate impaired the growth and general health of rats. Smith & Larson (1946) were, however, the first to study extensively this phenomenon in rats. They established that this condition manifested itself in the following two distinct and unrelated symptoms: (a) an anaemia, of the microcytic, hypochromic type, and (b) an inhibition of growth. The former syndrome could be prevented by supplementing the diet with low levels of copper, and liver extract could partially reverse the adverse influence on growth. van Reen (1953) found that at the 0-5-0-7 % level, zinc reduced liver catalase and cytochrome oxidase and that copper could counteract this influence of zinc. These studies indicated that toxic levels of zinc interfere with the utilization of copper and thus indirectly with the formation of iron-containing enzymes. van Reen & Pearson (1953) concluded, however, that the toxicity of zinc was not primarily due to disturbances in these enzyme levels. Such a conclusion is supported by the fact that serious impairement of growth occurs before reduction in any of the enzymes studied. Thus the underlying mechanisms in zinc toxicosis are not fully known. The situation is complex and although the studies of Smith & Larson (1946) have shown that liver extract is beneficial in zinc toxicosis, the factors responsible have not been characterized, nor is anything known concerning zinc toxicity in other species. In this paper, the results of investigations on zinc toxicity in the lepidopterous insect Corcyra cephalonica St. are presented. Although this organism is much lower in the evolutionary scale, it shows striking similarities (Sarma, 1955) to higher organisms like the rat in its nutritional requirements and metabolism.