Abstract
Hormonal control of larval colouration and behaviour in the common armyworm, Leucania separata, and L. loreyi associated with phase variation was analyzed. Extirpation of the suboesophageal ganglion (SG) reduced the intensity of the dark colouration in “gregarious” L. loreyi larvae. Implantation of SG from L. loreyi or L. separata larvae induced a dark colouration in the isolated abdomens of L. separata, whereas the implantation of SG from each of the 2 species induced only a slight darkening in L. loreyi. Dark colouration in L. separata “solitary” larvae was stimulated by the injection of the melanization and reddish colouration hormone (MRCH). However, the larvae did not show any active behaviour. The strain of L. separata lacking melanin which did not show any density-related darkening exhibited a more active behaviour depending on the population density. Implantation of SG from larvae lacking melanin induced a dark colouration in the isolated abdomens of normal larvae, but the effect on darkening was less pronounced than when SG from normal larvae was used. Moreover, neither SG from larvae lacking melanin nor from normal larvae induced an intensely dark colouration in the isolated abdomens of the larvae lacking melanin.
