The Growth of the Head Capsule of the Japanese Beetle Larva

The fact that the width of the head capsule of an insect larva is more or less constant for any instar of a species was first demonstrated by Dyar (1890) in his study of lepidopterous larva. This characterization of an instar by head measurements has recently been extended to a large number of species belonging to many orders of insects. The Japanese beetle passes through three instars in its larval development. In the present paper, an analysis is made of a large number of measurements of both the width and the length of the head capsule of the larva at different stages of development to determine if these measurements are characteristic of each instar and can be used to separate random samples of larvae into the three instars. This separation is possible only if there is no overlapping of measurements made on larvae of successive instars.