Exploring Potential of RNAi in two Major Cotton Bollworms Helicoverpa armigera and Earias vittella#

Abstract

Lepidopteran insects-pests such as Helicoverpa armigera and Earias vittella form the bollworm complex which attacks squares, flowers, and bolls, leading to substantial yield and quality losses in cotton. In non- Bt cotton era the damage caused by two bollworms such as H. armigera and E. vittella of this complex can translate into yield reductions often exceeding 30-60% under severe infestations if not managed effectively.
The Bt-cotton specifically BG-II expressing cry1Ac and cry2Ab genes have effectively managed the bollworm complex over the years. However, with the resistance development in pink bollworm to Bt-cotton, there is a high alert for the other two bollworms which are being effectively managed transgenic cotton till date. Thus alternative strategies are the need of hour to evolve eco-friendly and sustainable methods
for management of insect pests. RNA interference (RNAi) has emerged as a promising tool for developing novel pest management strategies against major lepidopteran pests such as H. armigera and E. vittella, both of which cause significant economic losses to crops like cotton and okra. However, variations in RNAi efficiency across insect species are often attributed to physiological barriers such as dsRNA-degrading
nucleases (DsRNases) present in gut fluids and hemolymph. In H. armigera and E. vittella, hemolymph was found to play a crucial role in diminishing the RNAi response, as the extent of dsRNA degradation increased with hemolymph concentration and incubation time. Conjugating dsRNA with chitosan nanoparticles effectively protected it from enzymatic degradation, substantially improving RNAi efficiency in both the pests. Targeting Aminopeptidase (AMN), Cadherin (CAD), and Alpha-amylase (AMY) genes through oral delivery of chitosan-coated dsRNA significantly enhanced silencing efficiency respectively, compared to naked dsRNA, while simultaneous knockdown of Cadherin and DsRNases further doubled silencing efficiency.