Juvenile hormone: Its assay and effects on pupae of Manduca sexta

Non-diapausing pupae of Manduca sexta were used to develop a bioassay for juvenile hormone (JH). The period of maximal sensitivity to Cecropia C17-JH injected in olive oil was found to be 24 to 30 hr after pupal ecdysis at the time of the beginning of epidermal retraction. The dose-response curves for C16-, C17-, and C18-JH at 29±1 hr after pupal ecdysis were determined and those for the latter two compounds were found to be similar and to be linear between 10^?2 and 10 μg/g body weight. C16-JH was 300 times less active than C17- and C18-JH in this bioassay. The effectiveness of 0·5 μg/g C18-JH at 29±1 hr was determined by the carrier media in which it was injected. The highest scores were obtained when the carrier was light mineral oil or loive oil whereas the lowest scores were obtained using 10% BSA or Tween 80. These scores are consistent with the kinetics of equilibration of the injected JH with the haemolymph. Thus, the injected hormone is more effective when it slowly leaks into the blood, presumably because it is metabolized much more slowly.