STRUCTURAL AND FUNCTIONAL CHARACTERISATION OF THE JUVENILE HORMONE BIOSYNTHESIS PATHWAY ENZYME FARNESOL DEHYDROGENASE FROM COTTON BOLLWORM HELICOVERPA ARMIGERA (HÜBNER)

Abstract

Helicoverpa armigera (Hübner), the cotton bollworm, is a polyphagous and destructive worldwide pest with a broad host range of over 180 plant species belonging to 47 families. The pest severely threatens global agriculture by infesting and damaging the reproductive and developmental organs of economically important crops such as cotton, soybean, tomato, pigeon pea, groundnut, maize, cowpea, sorghum, etc. These damages lead to significant worldwide economic losses, estimated at approximately 5 billion USD, making it a critical concern for global food security. Besides the broad host range, other major biological factors like high fecundity rate, interspecies hybridisation potential, high mobility, summer/winter diapause, and high frequency of developing resistance to various control measures contribute to the status of its global economic importance. In India, H. armigera infestations affect economically significant crops, including cotton, chickpea, pigeon pea, tomato, soybean, okra, corn, sunflower, and chilli, with yield losses ranging from 10-60% under normal weather conditions and up to 50-100% under conducive conditions. Currently, the integrated pest management (IPM) strategies for managing H. armigera entail the utilisation of chemical and biological insecticides alongside genetically modified Bt crops. Although biological control constitutes a crucial aspect of IPM, its widespread usage is hindered by limitations, including slow and expensive implementation, rendering it ineffective during pest outbreaks. Conversely, chemical insecticides are widely recognised as the most critical and extensively used global strategy, accounting for approximately 30% of the world's total pesticide usage for H. armigera. Notably, in countries like India and China, almost half of the total insecticides are dedicated to managing this pest alone. Unfortunately, the extensive use of various insecticidal chemicals/toxins has resulted in severe selection pressure, which has led to the rapid emergence of resistance to almost all commonly used insecticide classes, including Bt-toxins. Moreover, insecticide resistance reduces the efficacy of the employed insecticides, leading to increased usage and potentially causing significant harm to non-target organisms and the environment. Therefore, the pressing need to overcome the problem of insecticide resistance requires the development of novel insecticides with distinct mechanisms of action.