The Effect of Zinc and Potassium in the Nutrition of Tenebrio Molitor, with Observations on the Expression of a Carnitine Deficiency

Abstract

The investigation was prompted by the failure of the larvae of the mealworm, Tenebrio molitor to grow on synthetic diets and to develop deficiency symptoms in the absence of carnitine. The failure to grow was recognized as being caused by deficiencies of zinc and potassium. Zinc is an absolutely limiting factor, with 6 p.p.m. required for optimal growth, but with as little as 0.37 p.p.m. giving a growth response. The potassium requirements were determined as falling between 1.7 and 2.9% of the diet. A method for growing insects deficient in zinc or potassium has been described. The effects of different salt mixtures have been largely accounted for by their content of zinc and potassium. The effects of different proteins in the diet were accounted for by their content of zinc and carnitine. A new salt mixture has been described which at the 1 to 2% level allows optimal growth. Of 9 trace elements tested, zinc was the only one which could be demonstrated as being required as an addition to the diet. A clear-cut carnitine deficiency developed when Wesson's or the newly developed salt mixtures were used, but failed to develop in the presence of the McCollum-Davis salt mixture. Tenebrio grew on a semi-synthetic diet consisting of casein, glucose, cholesterol, 8 vitamins of the B complex and carnitine, and Wesson's or the new salt mixture, plus zinc, as well as on the best natural diets.