DOWN-REGULATION OF JUVENILE-HORMONE ESTERASE AND ARYLPHORIN PRODUCTION IN HELIOTHIS-VIRESCENS LARVAE PARASITIZED BY MICROPLITIS-CROCEIPES

Previous studies have shown that juvenile hormone esterase (JHE) activ ity and arylphorin titer were dramatically reduced in the hemolymph of Heliothis virescens larvae parasitized by Microplitis croceipes. Simi lar changes were observed in calyx fluid-injected or teratocyte-inject ed larvae. In this study, we showed that the mRNA levels of both JHE a nd arylphorin transcripts were reduced significantly in fat body of pa rasitized larvae compared to those in nonparasitized larvae. The reduc tion of mRNA level appears to be fat body-specific, because no reducti on of arylphorin mRNA level was observed in testes of the same parasit ized larvae. Significantly, the mRNA levels of JHE and arylphorin in c alyx fluid-injected or teratocyte-injected larvae were not different f rom those in control larvae, although the activity of JHE and the prot ein level of arylphorin were substantially lower in the treated larvae . Thus, our data suggest that both suppressed transcription of JHE- an d arylphorin-encoding genes and post-transcriptional/translational mod ification(s) of JHE and arylphorin mRNAs or proteins may be involved i n the reduction of JHE and arylphorin levels in parasitized H. viresce ns larvae. Calyx fluid and teratocytes may negatively regulate JHE and arylphorin levels via a post-transcriptional/translational mechanism. The factor(s) responsible for the reduction of JHE and arylphorin tra nscript levels by parasitization appears to be distinct from those ind uced by injection of calyx fluid or teratocytes. (C) 1996 Wiley-Liss, Inc.