Variation in larval gut bacteria between insecticide-resistant and -susceptible populations of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Abstract

Helicoverpa armigera (Hubner), a lepidopteron pest, causes enormous crop loss in India and elsewhere in the world in part because of resistance to various insecticides. The major mechanism of insecticide resistance is metabolic, genetic and behavioural modification. In the present investigation, we analysed the possibility of the involvement of gut symbiotic bacteria in insecticide resistance. Isolation of culturable bacteria from insecticide-resistant and -susceptible populations of H. armigera collected from crops in India resulted in 6 different species of bacteria isolated from resistant populations and only one from the susceptible laboratory-reared population. PCR-denaturing gradient gel electrophoresis (DGGE) was used to amplify the partial gene sequences of the 16S rRNA–V3 region. The banding pattern was analysed by using PAST software. Jaccard’s multivariate cluster analysis revealed that the resistant populations formed a group as did the susceptible population. The Raup and Crick bacterial similarity index showed that the resistant populations were similar in bacterial composition regardless of host plant. Gut microbiota of the resistant populations had the highest diversity index, followed by the moderately resistant and susceptible populations. Microbiota of the highly resistant population from Amreli (Gujarat State) had the highest diversity index, 2.30 (Shannon H). Six bacterial species were isolated from H. armigera larvae by culture. Four bacterial species had a long-term and mutual association with the H. armigera populations and some of the microflora associated with insecticide resistant populations differ quantitatively from insecticide-susceptible populations.