DIETARY INFLUENCE OF IRON FORMULATION ON THE DEVELOPMENT OF GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) IN LABORATORY COLONIES

Colonies of gypsy moth, Lymantria dispar (L.), reared on the standard wheat germ diet have been experiencing periods of unexplained slow asy nchronous development. The cause of the variability in development has been identified to be the variable nature of ferric phosphate provide d in the diet. As a separate ingredient or in a salt mixture, ferric p hosphate is a mixture of the amorphous and crystalline forms of this c ompound. Slow, asynchronous development occurred when ferric phosphate containing inadequate quantities of the amorphous form (6 mg/liter) w as used in the preparation of diet. When the amount of amorphous ferri c phosphate was higher, 35-49 mg/liter, larvae developed normally. Slo w, asynchronous development did not occur when diet containing suffici ent amorphous ferric phosphate was supplemented with extra crystalline ferric phosphate. Thus, the presence of crystalline ferric phosphate did not cause the developmental problems. Insects fed diet containing ferric citrate as a substitute for ferric phosphate, or Reck's mineral supplement containing ferrous sulfate, developed synchronously and fa ster than siblings fed diet containing inadequate amorphous ferric pho sphate, indicating that the iron component of ferric phosphate was the nutrient affecting synchrony and speed of development. The possibilit y of an iron deficiency caused by differences in bioavailability of am orphous and crystalline ferric phosphate is discussed.