RNA interference (RNAi) caused by exogenous double-stranded RNA (dsRNA) is a powerful tool, and to date is widely adopted to knockdown genetic targets crucial for growth and development of agriculturally important insect pests. Helicoverpa armigera is a pest feeding on more than 30 economically important crops worldwide and a major threat. Resistance to insecticides and Bt toxins is gradually increasing in the field. RNAi mediated knockdown of H. armigera genes by producing their dsRNA homologous to genetic target in bacteria has a high potential for insect management. A steroid signaling genes Ecdysone receptor (EcR), of H. armigera was selected as genetic target. Three different fragments comprising of a coding sequence of <450bp were cloned into the L4440 vector for dsRNA production in bacteria. The most effective fragment was further analyzed for post feeding effects on larval growth and development. After ingesting bacterial expressed dsRNA, mRNA levels of the target EcR gene declined dramatically resulting larval mortality and an abnormal development. Analysis of transcripts level by quantitative RT-PCR revealed that larval lethality was attributable to the knock down of genetic targets by RNAi. Results demonstrated that down regulation of H. armigera genes involved in transcriptional stimulation of development gene has aptitude as a bio-insecticide to control H. armigera population sizes and therefore decrease crop loss.