A metatranscriptomic survey of the invasive yellow crazy ant, Anoplolepis gracilipes, identifies several potential viral and bacterial pathogens and mutualists

Thriving populations of invasive species often decline, but the mechanisms behind such declines are rarely elucidated. The microbial community living within insects can have significant impacts on host health and population dynamics and may be one such mechanism. Here, we use Illumina RNAseq and 16S amplicon sequencing to compare the bacterial communities, and investigate the presence of viruses, in queens of the invasive yellow crazy ant, Anoplolepis gracilipes, from populations in various stages of decline or expansion in Australia. Black queen cell virus and sequences with homology to the Dicistroviridae family of viruses were detected in queens from declining ant populations. This is the first instance of sequences with homology to a virus being found in A. gracilipes and may indicate a new virus. The overall bacterial communities were not statistically different between the population types and a number of potential mutualists were discovered. Several putative pathogens were also detected, including Candidatus Rhabdochlamydia, the entomopathogen Serratia marcescens and the reproductive parasite Candidatus Cardinium. These taxa are known to significantly affect host biology in other organisms. Our survey has identified several candidates that may be responsible for population declines of this invasive ant, and therefore may have potential as biological control agents.