Diversity in gut microflora of Helicoverpa armigera populations from different regions in relation to biological activity of Bacillus thuringiensis δ-endotoxin Cry1Ac.

Transgenic crops expressing toxin proteins from Bacillus thuringiensis (Bt) have been deployed on a large scale for management of Helicoverpa armigera. Resistance to Bt toxins has been documented in several papers, and therefore, we examined the role of midgut microflora of H. armigera in its susceptibility to Bt toxins. The susceptibility of H. armigera to Bt toxin Cry1Ac was assessed using Log-dose-Probit analysis, and the microbial communities were identified by 16S rRNA sequencing. The H. armigera populations from nine locations harbored diverse microbial communities, and had some unique bacteria, suggesting a wide geographical variation in microbial community in the midgut of the pod borer larvae. Phylotypes belonging to 32 genera were identified in the H. armigera midgut in field populations from nine locations. Bacteria belonging to Enterobacteriaceae (Order Bacillales) were present in all the populations, and these may be the common members of the H. armigera larval midgut microflora. Presence and/or absence of certain species were linked to H. armigera susceptibility to Bt toxins, but there were no clear trends across locations. Variation in susceptibility of F1 neonates of H. armigera from different locations to the Bt toxin Cry1Ac was found to be 3.4-fold. These findings support the idea that insect migut microflora may influence the biological activity of Bt toxins.