Gut symbionts in the southern chinch bug

The southern chinch bug, Blissus insularis Barber, is a destructive insect pest of St. Augustinegrass and is notorious for developing resistance against major insecticide classes. It has specialized midgut crypts harboring Burkholderia symbionts that can degrade xenobiotic compounds, including insecticides. Using B. insularis as a model system, we sought to determine if Burkholderia mediate the observed insecticide resistance. We established laboratory colonies of bifenthrin-resistant (R) and susceptible (S) chinch bugs. Genomic DNA, extracted from the midgut crypts and reproductive tracts of both individual R and S females, were subjected to tandem PCR reactions using universal and genus-specific 16S primers. Analyses of 16S rRNA sequences showed that each female, regardless of its susceptibility to bifenthrin, harbored only a single Burkholderia ribotype in its crypts, whereas amplification of DNA from the female reproductive tract produced mixed sequence reads. Sequences of 16s rRNA gene from crypts of R and S chinch bugs did not form distinct clades in the phylogenetic tree. Methods to culture symbiotic Burkholderia were developed to examine and compare the structural and functional properties (i.e., multi locus sequencing typing, antibiotic susceptibility, chromosomal and plasmid profiles, and pesticide-degrading ability) of isolates from R and S chinch bugs. Our results highlight the high affinity between B. insularis and gut symbiotic Burkholderia, providing a valuable model to structure our understanding of insect-bacterium symbiosis.