Altstein, M., Department of Entomology, ARO, Volcani Center, Bet Dagan, Israel, Dept. of Entomology, ARO, Volcani Center, Bet Dagan 50250, Israel
Gazit, Y., Department of Entomology, ARO, Volcani Center, Bet Dagan, Israel
Aziz, O.B., Department of Entomology, ARO, Volcani Center, Bet Dagan, Israel
Gabay, T., Department of Entomology, ARO, Volcani Center, Bet Dagan, Israel
Marcus, R., Department of Statistics, ARO, Volcani Center, Bet Dagan, Israel
Vogel, Z., Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel
Barg, J., Cardiovasc. Hypertension Res. Lab., Wolfson Medical Center, Tel Aviv University Medical School, Holon, Israel

PBAN (also termed melanization and reddish coloration hormone, MRCH) is a cerebral factor known to regulate sex pheromone biosynthesis and cuticular melanization in moths. In the present study we developed a quantitative method (based on computerized image analysis of cuticles) to determine the effect of Helicoverpa zea PBAN (Hez-PBAN) on cuticular melanization and to study the structure-activity relationship of the neuropeptide in Spodoptera littoralis larvae. The results indicate that Hez-PBAN stimulates cuticular melanization in an interspecific manner, and that the minimal dose evoking formation of melanins is between 3-10 pmol/larva. Higher doses of Hez-PBAN did not stimulate melanization any further. Examination of the structure-activity relationship of Hez-PBAN revealed that the first eight N-terminal amino acids are not essential for the melanotropic activity and that the activity resides in the C-terminal region. Within this region the C-terminal amide was found to play a very important role. © 1996 Wiley-Liss, Inc.