Morphological colour change: Stage independent, optically induced ommochrome synthesis in larvae of the stick insect,Carausius morosus Br.

Summary The eyes of 4th, 5th, and 6th instar larvae of the stick insect,Carausius morosus, were partially covered with black varnish, and the ommochrome content of treated and untreated animals was determined throughout the instar. In untreated animals kept at 20°C in 16:8 LD the ommochrome content of the integument remains at the level found in newly hatched larvae (10 g/animal), up to the third moult, and increases only slightly (to 30 g) until the adult moult. Darkening the dorsal halves of the eyes does not influence the ommochrome content. Darkening the ventral halves, thus imitating the visual situation of an animal in light on a dark ground, causes after a lag of 3–4 days, a continuous increase of ommochrome content by about 5 g per day. The increase is equal at the beginning and during the second half of the 4th instar, and is also equal in the three instars investigated. Ommine and xanthommatine equally contribute to the increase.