Pheromone biosynthesis activating neuropeptide (PBAN) and colour polymorphism: an immunochemical study in Spodoptera littoralis

Abstract

PBAN (also termed melanization and reddish colouration hormone—MRCH) is a cerebral factor known to regulate sex pheromone biosynthesis, cuticular melanization and epidermal reddish brown pigmentation in moths. The ability of PBAN/MRCH to induce melanization suggests that it may play a role in colour polymorphism. In the present study we have examined the correlation between PBAN and colour polymorphism associated with phase (=density-induced) changes. Spodoptera littoralis larvae are dark when crowded and light when reared singly. We have compared the content of PBAN in haemolymph and head extracts of both crowded and isolated 6th larval instar. Analysis was performed by ELISA using an antiserum generated in our laboratory against Hez-PBAN (PBAN 1–33). The results revealed significantly higher levels of PBAN-like immunoreactivity in the head extracts of the light as compared with the dark larvae (634 ± 135 and 313 ± 84 fmol/head, respectively). By contrast, haemolymph content of PBAN/MRCH in singly-reared larvae was significantly lower than in crowded larvae (138 ± 28 and 268 ± 60 fmol/ml, respectively). Our results indicate that PBAN/MRCH is involved in colour polymorphism and suggest that this regulation occurs via control of the release of the neuropeptide to the haemolymph.