The Role Of Associated Bacteria Of Leptocybe Invasa Fisher&La Salle (Hymenoptera:Eulophidae) In The Resistance Of Its Host To Eucalyptus

Leptocybe invasa is a newly emerged invasive pest,which causes galls and results in reducing seedling and growth of Eucalyptus spp.L.invasa colonization may induce a series of physiological and biochemical changes in eucalyptus,including secondary substances.Many studies have shown that the associated bacteria might contribute to the adaption of insects to the host,by degrading these toxic substances in plants.Meanwhile,L.invasa has been known for its tolerance to host toxic substances,but little is known about the adaptation and bioactivities of associated bacteria when encountering host defensive chemicals.In current study,we measured the content of flavonoids and tannins of eucalyptus in response to the ingestion of L.invasa.Furthermore,the inhibition of flavonoids and tannins on the growth of the main associated bacteria of L.invasa and the ability of resistant bacteria to degrade flavonoids and tannins were also studied.The results were as follows:1.The result showed that the content of secondary metabolites of healthy eucalyptus was different in strains,and the content of flavonoids and tannins in the resistant eucalyptus species was significantly higher than that in susceptible ones..The content of secondary metabolites increased significantly after the susceptible strain was infested by L.invasa.2.We used the minimum inhibitory concentration to measure the toxicity of flavonoids and tannins to the associated bacteria of L.invasa.The results showed that S.cohnii and P.geniculate were resistant to higher concentration of flavonoids,whereas B.wiedannii,S.macescens and K.quasipneumoniae are more resistant to tannins..We conducted bacteriostatic experiments on flavonoids and tannins with different concentration gradients,and the results showed that bacteria could be killed under high concentration,while bacteria could survive and continue to reproduce under low concentration.3.Based on the previous bacteriostatic experiment,we selected flavonoids and tannins with appropriate concentration to conduct the biodegradation experiment.The results showed that both S.cohnii and P.geniculate had certain ability to degrade flavonoids,and their degradation rates reached 27.35%and 21.14%respectively at 24h.Two other bacteria,B.wiedannii and S.macescens,had strong ability to degrade tannin,their degradation rates reached 28.47%and 31.16%respectively at 24h,and reached 44.82%and 48.36%respectively at 48h.K.quasipneumoniae almost no longer degraded tannin after 12 hours.Collectively,L.invasa infected eucalyptus can induce resistance to eucalyptus.Eucalyptus produced a large number of secondary metabolites to resist the infection of L.invasa,and L.invasa associated bacteria can help L.invasa colonize eucalyptus by degrading secondary metabolites.