Biocontrol of insect pests in agriculture using chitinolytic enzyme complex of myrothecium verrucaria

Abstract

The agricultural pests and pathogens known so far include more than 2,000 species of insects and 800 fungi. The major insect pests which cause gt30% loss in yield in India are: Helicoverpa armigera on pulses, cotton, vegetables and sunflower, Spodoptera on vegetables, Pyrilla on wheat, rice, millet and sugarcane, recently introduced pest Ceratovacuna lanigera (woolly aphids) on sugarcane, mealy bug on cotton (Phenacoccus gossypiphilous) and grapes (Maconellicoccus hirsutus). While legumes such as groundnut, cowpea, etc. are prone to attack by soil-borne plant pathogenic fungi such as Sclerotium rolfsii, Fusarium oxysporum, Rhizoctonia solani and others. The development of resistance to chemical pesticides and negative impact of pesticides on the environment has prompted several researchers to evaluate alternative methods for the control of important agricultural pest’s .Interestingly, the protective covers of both insects and fungi, respectively viz; cuticle and cell wall share a common structural component chitin. The insect cuticle is composed of wax, lipids, protein and chitin. Chitin, one of the main components comprises of 25-50% of the insect cuticle. The fungal cell wall components comprise of skeletal and matrix constituents. Chitin and R-glucans are the main structural components while S-glucans and mannoproteins are the matrix components. In response to presence of chitin in the cell wall of fungal pathogens plants produce chitinases for their defense. The synergistic and/or consecutive action of different cuticle or fungal cell wall degrading enzymes viz chitinase, protease, lipase and b-1,3-glucanase comprising the chitinolytic enzyme complex are necessary as a killing component against the pests and pathogens. Therefore, while studying the chitinolytic enzyme complex the knowledge of other enzymes involved in cuticle and fungal cell wall degradation is also necessary.