Ecdysone and juvenile hormone activity in the larvae of the cockroach Periplaneta americana

Abstract

Changes in ecdysone and juvenile hormone titre during the 6th larval stage of the cockroach Periplaneta americana were studied. Juvenile hormone is secreted mainly in the second quarter of the instar, while the ecdysone titre increases gradually in the third quarter and reaches a maximum shortly before ecdysis. Following this period the titre of ecdysone drops rapidly and it is very low at the time of ecdysis. The increase in ecdysone concentration is correlated to the synthesis of the new cuticle and when the titre of juvenile hormone is at a low level. The maximal concentration of ecdysone and juvenile hormone were similar, about 30–35 ng per gram insect. In the larval stage, juvenile hormone exerts its effect at the beginning of the instar while ecdysone acts later.