Study On The Combined Application Of The Parasitoid, Scleroderma Guani And The Entomopathogenic Fungus, Beauveria Bassiana On The Control Of The Longhorn Beetle, Aphrodisium Sauteri

Aphrodisium sauteri,a major pest to oak trees in Huangshan Mountains,causes great damage in recent years.The present study shows the beetle is with a life cycle of 2 years, overwintering in its pupal chamber in xylem of the trunk as a larva of 4 or 5 instar.The adult initially emerges in the late May,peaks in the middle and late June,and oviposits in the early July.The egg hatches in the middle July.Aboundant host plant and suitable climate resulted in the beetle's wide distribution in Huangshan Mountains.The secluded larval stage in the trunk makes the beetle's control difficulty.The chemical volatiles extracted from fresh tissues of the host plant Quercus myrsinrefolia with N-hexane were indentified as Methyl Salicylate,(E)-2-Hexenal, o-Xylene,1-Hexanol,(Z)-Hex-3-en-1-ol,(E)-2-Hexen-1-ol,3,5-octadien-2-one,Benzyl Alcohol,Phenylethyl Alcohol,Salicylaldehyde,Benzyl Alcohol,(2E)-3,7-Dimethyl-2,6-octadien-1-ol,o-methoxy-pheno,methyl ester,Ethylbenzene and Butyl met-hacrylate by GC-MS analysis.The 16 identified volatiles provide the potential to do further study on efficient chemical attractants to the beetle.We tested the entomopathogenic fungus,Beauveria bassiana as a biological control agent against the feared longhorn beetle.Prior to a bioassay of B.bassiana strains against the larvae of A.sauteri,we cut down 8 target strains,all isolated from longhorn beetles,to 3 by some biological indices including morphologic observation,growth and germination speed,sporulation,UV resistance as well as producing level of extracellular protease. Finally,the selected strain Bb202 showed high virulence to the target beetle with a corrected mortality of 92.8%,an infection ratio of 93.3%,and a LT₅₀(time needed for 50% mortality) of 5.86d at the concentration of 1×10⁷ conidia /ml,which provides great potential for sustainable control of A.sauteri in a forest.The parasitic ratio of the parasitoid,Scleroderma guani on A.sauteri was positively related to its inoculation number to the beetle,which ranged from 2:1～5:1.Combined application of S.guani and B.bassiana could significantly improve the mortality of A. Sauteri.We set 3 concentrations of 1×10⁶conidia/ml,1×10⁷conidia/ml,and 1×10⁸ conidia/ml to test dosage effect of B.bassiana on mortality of the beetle's 4th instar larvae, and mortalities of 71.2%,86.7%and 93.3%were gotten,respectively,at the 7th day after inoculation,much higher than the mortality of 53.3%inocualted S.guani alone.The coordinated attack of S.guani and B.bassiana upon A.sauteri also appeared in the field trial,in which the combined application of B.bassiana and S.guani caused a mortality of 56.5%～60.1%,while applying S.guani alone only resulted in a much lower mortality of 39.8%.Monitoring the tree mortality in the field trial for 2 years,we found applicatom of S. guani and B.bassiana could significantly decrease the tree mortality caused by A.sauteri. Almost no dead tree was found in the treatment plots B and C,which had a significant difference to the control plots.The control plots still had a high tree mortality without difference to that in two years.