[Aim] Leptocybe invasa is an emerging invasive pest, which causes galls and reduces seedling growth of Eucalyptus spp. The purpose of this study was to investigate the role of associated bacteria in the adaptation of L. invasa to its host plant.[Method] First, we measured the content of flavonoids and tannins of eucalyptus in response to damage by L. invasa. Furthermore, the inhibition of flavonoids and tannins on the growth of the main L. invasa-associated bacteria and the ability of bacteria to degrade flavonoids and tannins were studied.[Result] Flavonoid and tannin content in the resistant eucalyptus species was significantly higher than in susceptible ones. Staphylococcus cohnii and Peseudomonas geniculate were resistant to higher concentrations of flavonoids, whereas Bacillus wiedannii, Serratia macescens and Klebsiella quasipneumoniae were more resistant to tannins. Correspondingly, all of these resistant bacteria were able to degrade these allelochemicals. Base on that, Staphylococcus cohnii had a stronger ability to degrade flavonoids than Pseudomonas geniculate, and B. wiedannii and Serratia macescens had stronger abilities to degrade tannins than Klebsiella quasipneumoniae.[Conclusion] Flavonoids and tannins are the key allelochemicals ineucalyptus in response to the infection by L. invasa. Furthermore, the associated bacteria might contribute to the adaptation of L. invasa to its host, by degrading these allelochemicals.