Head-Capsule Measurements of Southern Armyworm Larvae (Prodenia Eridania (Cramer))

Abstract

The observation by Dyar (1890) that the sclerotized parts of insects do not change in area during a stadium but increase only at ecdysis led to the generalization that the changes in width of the head capsule of a larva in its successive stages usually follow a regular geometric progression, and this generalization has become known as Dyar's rule. This rule has been used by Taylor (1931), Gaines and Campbell (1935), Peterson and Haeussler (1928), and others to determine the number of instars undergone by certain larvae and also to determine if the observed number of molts coincided with the number required if Dyar's rule was applicable.