INDUCTION OF VITELLOGENIN SYNTHESIS IN LOCUSTA-MIGRATORIA BY THE JUVENILE-HORMONE ANALOG, PYRIPROXYFEN

Several aspects of the activity of the juvenile hormone mimic, pyriproxyfen, particularly relate to the induction of vitellogenin synthesis in the fat body, have been studied in Locusta migratoria. After topical application in acetone to the neck cuticle of adult locusts, pyriproxyfen is taken up rapidly, reaching roughly constant levels in hemolymph and fat body in 6 h. For induction of vitellogenin synthesis in fat body, and for accumulation of vitellogenin in hemolymph, the ED50 in adult females is 2.3 mug, whereas adult males produce no vitellogenin with doses up to 300 mug. In fifth-instar larvae, in contrast, the ED50 in females is about 30 mug, and males can also be induced to produce vitellogenin, but in a smaller amount which may be related to gene dosage. With pyriproxyfen, as with methoprene, there is a lag of about 24 h before vitellogenin appears in hemolymph after primary stimulation and a reduced lag time after secondary stimulation. The accumulation of vitellogenin mRNA in fat body, assayed by hybridization with a DNA probe, shows a lag of nearly 24 h, which is extended when protein synthesis is temporarily blocked with cycloheximide. The parallel responses to pyriproxyfen and to methoprene in several different tests suggest that, despite their different structures, both compounds share the same primary mode of action, which is believed to correspond to that of natural juvenile hormone.