Down-regulation of juvenile hormone esterase and arylphorin production inHeliothis virescens larvae parasitized byMicroplitis croceipes

Abstract

Previous studies have shown that juvenile hormone esterase (JHE) activity and arylphorin titer were dramatically reduced in the hemolymph of Heliothis virescens larvae parasitized by Microplitis croceipes. Similar changes were observed in calyx fluid-injected or tetratocyte-injected larvae. In this study, we showed that the mRNA levels of both JHE and arylphorin transcripts were reduced significantly in fat body of parasitized larvae compared to those in nonparasitized larvae. The reduction of mRNA level appears to be fat body-specific, because no reduction of arylphorin mRNA level was observed in testes of the same parasitized larvae. Significantly, the mRNA levels of JHE and arylphorin in calyx fluid-injected or teratocyte-injected larvae were not different from those in control larvae, although the activity of JHE and the protein level of arylphorin were substantially lower in the treated larvae. Thus, our data suggest that both suppressed transcription of JHE- and arylphorin-encoding genes and post-transcriptional/translational modification(s) of JHE and arylphorin mRNAs or proteins may be involved in the reduction of JHE and arylphorin levels in parasitized H. virescens larvae. Calyx fluid and teratocytes may negatively regulate JHE and arylphorin levels via a transcriptional/translational mechanism. The factor(s) responsible for the reduction of JHE and arylphorin transcript levels by parasitization appears to be distinct from those induced by injection of calyx fluid or teratocytes. © 1996 Wiley-Liss, Inc.