Molecular identification of insecticide degradation by gut bacteria isolated from helicoverpa armigera of cotton plants

Abstract

The cotton bollworm Helicoverpa armigera occurs as a major pest in many economically important crops, including cotton, pigeon pea, chickpea, pea, cowpea, sunflower, tomato, sorghum, pearl millet and other crops. Intestinal microorganisms play important role in the degradation of diet components of insects. In order to know the role of gut bacteria in insecticide resistance five insecticides Chlorpyriphos (20% EC), Cypermethrin (25% EC), Malathion (50% EC), Quinalphos (25% EC), Triazophos (40% EC), were selected for the insecticide degradation studies. All the bacterial isolates from the gut of lab and field populations of H. armigera were identified using 16S rRNA gene-based identification and tested for their growth on minimal salt medium (MSM) along with the selected insecticides. A total of 11 bacterial isolates were tested and among them, isolate CL4 (Rhodococcus sp.) was found to grow on minimal salt medium (MSM) and with chlorpyriphos and isolate CL2 (Enterococcus casseliflavus) was able to grow in MSM with chloropyriphos (C22H19Cl2NO3) and malathion (C10H19O6PS2) and no growth was seen in MSM without insecticide (control). Gas Chromatography analysis of the positive bacterial isolate cultures in MSM showed that the isolate CL4 (Rhodococcus sp.) was able to utilize 43.9% of chlorpyriphos and isolate CL2 (E.casseliflavus) was able to utilize 26% of chlorpyriphos and 57.1% of malathion in MSM broth cultures with comparison with the respective control cultures. Findings of the current work suggested that gut bacteria in the field populations of H. armigera plays a role in insecticide resistance.