Defense and melanization depend on the eumelanin pathway, occur independently and are controlled differentially in developing Ceratitis capitata

A defense mechanism in the hemocytes and cuticle of developing Ceratitis capitata has been demonstrated (Marmaras and Charalambidis, 1992; Marmaras et al., 1993a; Marmaras et al., 1993b). To elucidate further the mechanism and the regulation of defense reactions, we studied this process in relation to melanization in the major larval tissues, in two distinct developmental stages; the feeding and wandering larval stages. The results demonstrate that defense reaction depends on reactive tyrosine derivatives of either early or late stages of the sequence of reactions involved in eumelanin biosynthesis. However, defense and melanization occur independently e.g. hemocytes exhibit a high degree of Escherichia coli immobilization and entrapment, but not any ability to biosynthesize melanin. Serum on the other hand, showed a high degree of melanin formation in wandering stage larvae, but had not any ability for E. coli immobilization. In integuments of wandering stage larvae, both processes occur simultaneously. These findings suggest independent control mechanisms for these processes. Indeed, our results suggest that defense seems to be controlled by the presence of proteins responsible for nonself recognition and melanization by developmental regulation of dopachrome conversion factor.