dsRNA-based Approaches to Biopesticide Development for Helicoverpa armigera Control

Abstract

Crop protection is a global priority due to the significant damage inflicted by insect pests. Among them, Helicoverpa armigera, a lepidopteran pest, causes substantial yield losses in key crops such as tomatoes, cotton, and maize, resulting in an annual cost of around US$5 billion. This thesis investigates RNA interference (RNAi) as a sustainable pest control approach, focusing on suppressing essential gene expression in H. armigera using dsRNA, while also assessing the biosafety implications on non-target organisms (bumblebees). dsRNA molecules homologous to the potassium ion channel (K+) and fibroblast growth factor (FGF) gene transcripts were introduced to H. armigera larvae through microinjection or feeding, or to eggs via soaking. Microinjection without formulation significantly impacted larval survival and led to the downregulation of both K+ and FGF genes. Microinjection with chitosan formulation, however, had no discernible influence on survival, although gene expression data for this condition were unavailable. Feeding experiments with or without formulation did not significantly affect the survival of either target. However, gene expression quantification revealed downregulation of K+ and FGF genes under both feeding conditions, indicating thew potential efficacy of this method. Stability assessment indicated that non-formulated dsRNA was susceptible to degradation in gut juice, while haemolymph exposure had minimal impact. Similarly, formulated dsRNA was susceptible to gut juice degradation, with haemolymph having little effect. Egg-related experiments demonstrated significant effects of both formulated and non-formulated dsRNA treatments on hatching rates. Gene expression quantification through egg soaking revealed K+ gene downregulation with both types of dsRNA, along with significant knockdown with non-formulated dsRNA. The FGF gene showed significant downregulation with both dsRNA treatments. Biosafety evaluations encompassing survival and gene expression quantification indicated no noticeable effects from dsRNA treatments, suggesting a minimal impact upon Bombus terrestris. These results provide a comprehensive perspective encompassing pest control effectiveness and ecological concerns, thereby enhancing the practicality and sustainability of this innovative strategy.