A compound with insect-molting hormone activity extracted from Podocarpus gracilior Pilger was identified as ponasterone A by thin layer chromatography. Topical applications had no effect on the eggs or larvae of the navel orangeworm, Paramyelois transitella (Walker). Premolt sclerotization was induced in sixth instar larvae by intrahemocoele injection and 0.5 µl produced the greatest response. A larval-pupal intermediate was the most common type of premature development induced by the compound. Isolated abdomens from larvae with thoracic ligatures were highly sensitive to the phytoecdysone and were used to detect molting hormone activity. Ponasterone A applied to the larval stage by injected and oral dosages reduced the fecundity of the female survivors. The phytoecdysone had no effect when incorporated in the larval diet.