VARIABILITY IN JUVENILE-HORMONE PRODUCTION BY LOCUST CORPORA ALLATA KEPT IN-VITRO FOR LONG PERIODS

Juvenile Hormone III (JH-III) production by corpora allata (CA) of sex ually mature female locusts (Locusta migratoria migratorioides (R. & F .)) was maintained in vitro for up to 30 days in an agar-solidified me dium. Hormone production was measured periodically with a short-term r adiochemical assay. Low-activity CA increased their activity significa ntly after 24-48 h incubation in the long-term medium, but high-activi ty glands did not. Variations in activity were considerable among glan ds tested on the same day and among measurements from the same gland o n different days. Farnesoic acid-stimulated rates of JH-III production were always higher than the basal rates, suggesting that the CA were not maximally activated. However, freshly excised low-activity CA, who se hormone production increased in the long-term conditions, showed si milar farnesoic acid-stimulated rates of JH-III production to those of freshly excised high-activity glands, suggesting that at the time of excision of the corpora allata rate-limiting step(s) preceding farneso ic acid biosynthesis were inhibited or refractory to stimulation in vi vo.