Abstract: The juvenile hormones (JHs) and molting hormone 20-hydroxyecdysone (20-E) from Bemisia tabaci nymphs and adults un-parasitized or parasitized by Encarsia bimaculata  were measured with RP-HPLC. The results indicated that the parasitized older nymphs had significantly higher titer of JHs (P<0.05) but sign ificantly lower titer of 20-E (P<0.05) than those un-parasitized older nymphs (CK), which had similar titers of JHs and 20-E with the un-parasitized younger nymphs. This suggested that E. bimaculata could modulate its host metamorphosis hormone level, and prolong the nymph stage of its host. JH titers between adults,‘pupae' and CK, and 20-E titers between‘pupae' and CK of  B. tabaci, however, were not significantly different (P>0.05). 22Refs. In Chinese.

Key words: Encarsia bimaculata, Bemisia tabaci, juvenile hormones, 20-hydroxyecdysone, titer