Diversity of gut–microorganisms in Bt–resistant and Bt–susceptible larvae of the maize stem borer (Busseola fusca) (Lepidoptera : Noctuidae)

Abstract

Maize is one of Africa’s main food sources. It is therefore important to protect this crop against pests such as the maize stem borer Busseola fusca. Genetically modified Bacillus thuringiensis (Bt) maize has been shown to be very effective against pests like B. fusca. However, this pest developed resistance to Bt–maize. The current study was inspired by the lack of knowledge on microorganisms associated with these insects as they play a vital role in the growth and development of herbivorous insects. The aim of the study was to determine and compare the community diversity of microorganisms present in the midgut of resistant and susceptible B. fusca larvae. Secondly Escherichia coli and Enterobacter spp. present in the midgut were quantified and compared with community diversity obtained with DGGE analysis. The midgut of B. fusca was removed after which DNA was extracted from the contents. Extracted DNA was subjected to Polymerase Chain Reaction Denaturing Gradient Gel Electrophoresis (PCR–DGGE) analysis after which prominent bands were excised and sequenced. Serial dilutions were also done of the contents of the midgut and plated out on Brilliant Green Bile agar and mFc agar for quantification. DGGE analysis showed no differences in the community structure of the midgut contents of Bt–resistant or susceptible B. fusca reared under either laboratory, greenhouse or field conditions. Sequencing results revealed the dominance of Enterococcus spp., specifically Enterococcus mundtii, Enterococcus faecalis, Enterococcus faecium, Enterococcus hirae and Enterococcus durans. Other organisms isolated included Staphylococcus sp., Agrobacterium tumefaciens, Leuconostoc mesenteroides, Peptostreptococcaceae bacterium and several uncultured bacteria. Quantification of E. coli and Enterobacter spp. suggested that Bt–maize and environmental factors might play a role in the abundance of these organisms in the midgut. Dominance by E. coli and Enterobacter spp. might suppress the growth of other bacteria in the midgut.