Microbial Diversity Of Solenopsis Invicta Nests And Its Inhibitory Effect On Pathogen Infection

Solenopsis invicta（Buren）is one of the most harmful invasive alien species published by the International Union for Conservation of Nature.Their fierce habit and high reproductive capacity were harm and threaten to agriculture,forestry and safety of human and ecosystem seriously.Some biological control to it have been studied,but biological control effect in field were lower than it in lab.That restricted the application of biological control to S.invicta severely.Besides the abiological factor,which may be related to ant-nest microorganisms.In this study,the pathogenicity of Metarhizium anisopliae（Metschnikoff）and Beauveria bassiana（Balsamo）Vuillemin to the S.invicta were tested.Analyzed the diversity of S.invicta ant-nest microorganisms,and verified their inhibitory to pathogenic fungus.it has established theoretical foundation for controlling to S.invicta with pathogenic fungus.All the results as follows:（1）The pathogenicity of 11 B.bassiana strains and 9 M.anisopliae strains to S.invicta was determined by the soaking method.The results showed that the corrected mortality rate of B.bassiana strains and M.anisopliae strains to worker ants of S.invicta varied from（6.47±0.98）%–（67.14±0.22）%and（35.13±1.25）%–（81.93±0.94）%.Among all strains tested,Ma Wys-01 exhibited the strongest pathogenicity to S.invicta.The pathogenicity of different concentrations of Ma Wys-01 strain to red fire ant worker ants was analyzed.At 3,6 and 10 days after inoculation,the median lethal concentrations of S.invicta workers were 7.59×10⁸、2.42×10⁵and5.90×10⁴ spore·m L^–1,respectively,and the peak period of death of worker ants of S.invicta was on the fourth day after inoculation.The death peak of the worker ants of S.invicta after the inoculation was on the 4th day.（2）402 microorganisms strains were isolated from soil of inside and outside ant-nest in sandy soil,clayey wasteland and loamy grassland,respectively.And 128 particular culturable strains inside ant-nest soil were isolated,including fungi 52 strains,actinomycetes 61 strains and bacteria14 strains.Comparing the microbial diversity of soil inside and outside the nest by High-throughput sequencing,it was found that 212fungal genera were found inside and outside the nest in the sandy field area,and the richness of Penicillium,Talaromyces,Cunninghamella,Gymnascella were significantly greater than that outside the nest.There were 887 bacteria genera,actinomyces inside and outside the nest,and the richness of 21 genera,including Marmoricola,Cupriavidus,Smaragdicoccus,etc.were significantly higher than that outside the ant-nest.In the clayey wasteland,there were 125 fungal genera were found inside and outside the nest,there were 17 genera with significant differences in richness inside and outside the nest,which the richness inside the nest of Mortierella and Monocillium was significantly higher than that outside the nest.There were 205 actinomyces inside and outside the ant-nest,but only the richness of Nocardioides and Arthrobacter inside were significantly higher than that outside the ant-nest.In the loam lawn,there were 224 fungal genera inside and outside the ant-nest,there were 35genera with significant differences in richness inside and outside the nest,and the richness of 13 genera,including Knufia,Haematonectria,Ophiocordyceps,Cunninghamella,Lecanicillium,etc.were significantly higher than that outside the ant-nest.There were 119 actinomyces inside and outside the ant-nest,and the richness of 6 genera,including Arthrobacter,Acidimicrobiales unclassified,Cleroflexi unclassified were significantly higher than that outside the ant-nest.It can conclud that the microflora species and the dominant microflora of inside ant-nest and outside were significant differences in among region.Analyzed the diversity of microorganism inside and outside the ant-nest of S.invicta in three areas.In the sandy field,the diversity and richness of fungi in ant-nest were significantly higher than those outside.In the clayey wasteland,the diversity and richness of fungi in the ant-nest were significantly lower than those outside.In the loam lawn,the diversity of fungi inside and outside were no significant difference,but the uniformity inside was significantly lower than outside.The Shannon index and Simpson index of bacteria and actinomycetes inside were no significant difference from outside the in each region,It showed that the diversity and uniformity of bacteria and actinomycetes inside were consistent with them outside ant-nest in the same region.（3）The fermentation liquid of ant-nest soil different microorganism strains were determined to the effect on spore germination of M.anisopliae Ma Wys-01.The results showed that fermentation liquid of bacteria and actinomycetes inside ant-nest were no significant inhibitory to Ma Wys-01spore germination after 48 h.But the fermentation liquid of 15 fungi strains were significantly inhibitory to the spore germination,and the strain PSHC-1,PDHC-9,MHYC-9 were stronger inhibitory,with the Ma Wys-01spore germination rates were 1.31%,25.91%,and 13.92%,respectively,which were significantly lower than it of the control（93.51%）.Inhibiting effect of 3 stronger inhibition strains fermentation liquid on the Ma Wys-01spore germination were determined with different concentrations,the spore germination rate was increased with fermentation liquid concentrations declining.After 48 h,the fermentation liquid of strain PSHC-1 was significantly inhibited the spore germination under every concentrations,the germination rate was only 27.67%when the fermentation liquid concentration was 10%.Below 20%fermentation liquid of PDHC-9inexistence inhibited to Ma Wys-01 spore germination.It did not affect on the Ma Wys-01 spore germination when fermentation liquid concentration of MHYC-9 was below 10%.By observing the morphological characteristics of spores germinating,the PDHC-9 and MHYC-9fermentation liquid caused Ma Wys-01 spores expanding and distortion during germinating,and mycelial base moniliform else.However,the PSHC-1 fermentation liquid could not;It indicated that some ant-nest fungi may inhibit M.anisopliae spores germination,or cause pores and mycelium to distortion during the growing,thus reduced the M.anisopliae spores survival and infectivity to S.invicta in the field possibly.