ABSTRACT
The cotton bollworm, Helicoverpa armigera, is a highly polyphagous pest, causing enormous losses to variouseconomically important crops. The identification and in vitro functional validation of target genes of a pest is aprerequisite to combat pest via host-mediated RNA interference (RNAi). In the present study, six hormonalbiosynthesis genes of H. armigera were chosen and evaluated by feeding insect larvae with dsRNAs corresponding to each target gene, viz., juvenile hormone acid methyltransferase (HaJHAMT), prothoracicotropichormone (HaPTTH), pheromone biosynthesis-activating peptide (HaPBAP), molt regulating transcription factor(HaHR3), activated protein 4 (HaAP-4) and eclosion hormone precursor (HaEHP). The loss of function phenotypes for these hormonal genes were observed by releasing second instar larvae on to artificial diet containingtarget gene-specific dsRNAs. Ingestion of dsRNAs resulted in mortality ranging from 60% to 90%, reduced larvalweight, phenotypic deformities and delayed pupation. The quantitative real-time PCR (qRT-PCR) analysisshowed that the target gene transcript levels were decreased drastically (31% to 77%) as compared to control orunrelated control (GFP-dsRNA), and correlated well with the mortality and developmental defects of larvae.Also, a comparison of the silencing efficacy of un-diced long HaPTTH-dsRNA with RNase III diced HaPTTHdsRNA (siRNAs) revealed that long dsRNAs were more efficient in silencing the target gene. These resultsindicated that the hormonal biosynthesis genes have varied sensitivity towards RNAi and could be the vital targetsfor insect resistance in crop plants like cotton which are infested by H. armigera