Microbial agents against Helicoverpa armigera: Where are we and where do we need to go?

Plants are prone to various biotic stresses in nature by bacteria, viruses, fungi, parasites, harmful insects and weeds. The biggest percentage loss (70%) in plants is attributed to insects. Lepidoptera is one such diversified phytophagous insect group, which include Helicoverpa armigera, a key pest of many food crops including chickpea, pigeonpea, pea, lentil, chillies, sunflower, tomato, tobacco and cotton. Controlling this insect has been a big task for farmers leading to the manufacture of a plethora of pesticides. However, over reliance on chemical pesticides has resulted in problems including safety risks, environmental contamination, outbreaks of secondary pests, insecticide resistance and decrease in biodiversity. Hence, there is an urgent need for the development of eco-friendly methods such as entomopathogens, antagonist or competitor populations of a third organism and botanicals to suppress H. armigera. Also, many compounds from microorganisms have been found to be effective in crop production, and these have a role in controlling H. armigera. The actinomycetes play an astounding role in controlling the key plant pathogens. They are the representative genera of higher microbial mass in the soil. Numerous studies have shown that these productive actino-bacteria can generate an impressive array of secondary metabolites such as antibiotics, antitumor agents, insecticides etc. This review emphasizes the mechanism behind resistance to insecticides along with actinomycetes and its potential as a biocontrol agent against H. armigera