Effects of Inadequate Feeding on Insect Metamorphosis

Abstract

SOME years ago H. S. Pruthi pointed out^1,2 that moulting in insects is not the result of growth, but is “primarily concerned with metabolism”. He found that intermittent starvation of the larvæ of Tenebrio molitor extended the duration of the larval period and increased the number of moults, the size and weight before pupation of the older larvæ being the same as in the younger ones. Partially starved larvæ of Pieris brassicce also showed an increased number of moults, the size and weight before pupation being the same as in normally fed caterpillars used for control experiments. Pruthi therefore concluded that if “moulting is simply to allow growth, there is absolutely no necessity for extra moults” and expressed the opinion, based on observations detailed in his paper,¹ that if larvæ are starved before the commencement of the metamorphic processes pupation is delayed, while if they are starved after maturity pupation is accelerated. On the other hand, as he himself shows, several workers contradict the theory that inadequate feeding, quantitatively or qualitatively, delays metamorphosis.