The head capsule widths of larvae of the cowpea pod-borer Maruca testulalis, reared individually and crowded together in the laboratory were measured. The measurements were subjected to a test of analysis of variance, frequency distribution and Dyar's rule. All methods gave a total of five larval instars in the life cycle and conformed to Dyar's rule. There was a high positive correlation (r = 0.97) between the size of the head capsule and the period of development elapsing. The minimum duration of larval development was 9 days.
