MOLECULAR CHARACTERISATION AND FUNCTIONAL STUDIES ON CRUCIAL CHITIN BIOSYNTHESIS PATHWAY GENES FROM COTTON BOLLWORM HELICOVERPA ARMIGERA (HÜBNER)

Abstract

The Old World cotton bollworm, Helicoverpa armigera (Hübner), is a destructive pest known to infest over 300 plant species across 68 families worldwide, including cotton, corn, tomato, sorghum, pea, and soybean. Its infestations cause substantial crop damages estimated at a staggering 5 billion US dollars per year. H. armigera is known for its high reproduction rates, ability to migrate long distances, and facultative diapause, these factors contribute to its dominance as a pest. One concerning characteristic of this pest is its propensity to develop resistance to contemporary insecticides and even Bt-toxin, posing a challenge for pest management efforts. Hence, there is a pressing need to explore alternative pest management strategies to complement existing methods and ensure effective control of this damaging pest. In this regard, RNA interference (RNAi) technology has emerged as a powerful tool for functional genomics and pest management, wherein double-stranded RNA (dsRNA) is introduced into host organisms to trigger sequence-specific post-transcriptional gene silencing. However, the success of RNAi in insects depends on effective dsRNA delivery methods. Microinjection is an extensively employed approach for delivering dsRNA in insects, but it is largely expensive because of the need for sophisticated microinjectors, making it less accessible for resource-poor laboratories. Therefore, in this thesis work, we have demonstrated a simple and cost-effective dsRNA injection method using an insulin-injection syringe and fabricated micropipette tips. We validated our dsRNA delivery method by examining the gene expression profile of Argonaute 1 (ago1), a core RNAi response, as an indicator of RNAi efficiency. Additionally, we evaluated the phenotypic effects of dsRNA injections targeting key chitin biosynthesis genes from H. armigera, a major pest species.