The Location of the Photoperiodic Receptors in the Aphid <i>Megoura Viciae</i> Buckton

Abstract

ABSTRACT Although the photoperiodic reactions of insects and mites have been studied quite extensively (Lees, 1955 ; de Wilde, 1962), the site of the photoreceptors is still unknown. The light pathway does not seem to involve the eyes. Thus Tanaka (1950) observed that the photoperiodic control of diapause in the silkworm Antheraea pernyi was not affected by cauterizing the lateral ocelli of the 4th-instar larva—a treatment that resulted in the complete disappearance of these organs in the following instar. De Wilde, Duintjer’ Mook (1959) have shown that adult Colorado beetles (Leptinotarsa decemlineata) respond normally to day-length after the compound eyes have been covered with black paint or destroyed with a cautery. Less progress has been made in identifying the regions of light sensitivity. Geispits (1957) was able to fit an opaque hood over the head of a Dendrolimus larva which was otherwise continuously illuminated. With this covering in place for 12 hr. daily all the insects subsequently entered diapause. But none did so when only the body was shielded from light, showing that the photoreceptors were located on the head. Since the wavelength sensitivity of the visual and photoperiodic response showed some correspondence Geispits was led to the further conclusion that the eyes were in fact the photoperiodic receptors. But in view of the preceding evidence this conclusion seems questionable.