Abstract:
The Eucalyptus snout beetle is an oligophagous invasive insect pest of Eucalyptus species. The beetle is attracted to emerging leaves containing high concentrations of essential oils consisting of a complex mixture of mono and sesquiterpenes. In Eucalyptus, terpenoids can function as insect repellents through powerful odours and bitter taste. Furthermore, on a molecular scale, terpenoids are involved in breaking down cell membranes and negatively affecting ion transport. Regardless of the elaborate chemical defences of Eucalyptus species, the Eucalyptus snout beetle is able to tolerate and overcome high concentrations of terpenoids. We, therefore, hypothesize that the microbial communities associated with the gut of Gonipterus spp. are involved in secondary metabolite detoxification. Gonipterus sp. n. 2 adults were reared on two Eucalyptus genotypes with significantly different biochemical profiles. Metabolomic analysis of the leaf and beetle frass profiles indicated that there was a dramatic decrease in terpenoid concentrations from leaf to frass. Moreover, several biotransformation products of eucalyptol, α-pinene and d-limonene were found in the frass, suggesting that Gonipterus sp. n. 2 gut microbial communities may facilitate in Eucalyptus secondary metabolite detoxification. Following this discovery, a 16s rRNA gene sequencing approach was used to investigate the bacterial diversity of the host plants, gut and frass of Gonipterus sp. n. 2. Additionally, to determine if the Gonipterus gut microbial communities detoxified Eucalyptus secondary metabolites in vivo, an attempt was made to disrupt the gut bacterial community through antibiotic treatment. Sequencing results indicated that plant bacterial communities were enriched with Clostridiales and Sphingomonadales whereas gut and frass associated bacterial communities were dominated by Enterobacteriales. Furthermore, a core gut microbial community was detected, with a large percentage of the bacterial families shared between the Gonipterus beetle groups despite diet differences. Antibiotic treatment failed to disrupt the gut microbial communities of Gonipterus sp. n. 2, as no significant difference was observed between antibiotic and control beetle treatments. Therefore, more research is required to determine the role of Gonipterus gut microbial communities in detoxifying Eucalyptus secondary metabolites
