Screening And Pathogenicity Of Beauveria Bassiana For High Virulence Strains Of Eurydema Gebleri

Eurydema gebleri belongs to the genus Eurydema of Hemiptera,with the piercing-sucking mouthpart.At present,E.gebleri is controled by chemical and agricultural methods.Chemical pesticides have good control effect on E.gebleri,but they are easy to produce resistance.And the effect of agricultural control is slow and the workload is heavy.Therefore,people pay attention to the biological control against pests of Hemiptera.Beauveria bassiana is a broad-spectrum entomogenous fungus and exists widely in nature.It can control the pests of Lepidoptera,Hymenoptera,Coleoptera efficiently.However,there are few studies about B.bassiana against Hemiptera pests.In this study,E.gebleri and B.bassiana were employed.The high virulence of B.bassiana strains to adults of E.gebleri was screened by bioassay.The pathogenic mechanism of B.bassiana was studied by stereomicroscopy and scanning electron microscopy.This study can provide data references and theoretical basis for screening highly virulent,and enriching the biocontrol technology of Hemiptera pests.1.Screening of high-virulence strains against E.gebleriB.bassiana FDB,BF and TST were employed in virulence screening.Corrected mortality and median lethal time(LT₅₀)of E.gebleri were determined.The corrected death rates of E.gebleri infected by FDB,BF and TST were 96.30%,85.19%,and 77.78%,respectively.And the median lethal times were 4.398d,4.871d,and 4.844d,respectively.The results showed that the FDB strain is the high-virulence strain.2.Pathogenicity of B.bassiana strainsE.gebleri was infected with spore suspension of strain FDB,and the corrected mortality of E.gebleri was determined.The result showed that the corrected mortality of 1×10⁵,1×10⁶,1×10⁷ and 1×10⁸spores/m L was 29.63%,55.56%,62.97% and 96.30%,respectively.The half lethal concentration(LC₅₀)was 8.48×10⁵ spores/m L.3.Observing the growth of B.bassiana on the surface of host with stereomicroscopeThe spore suspension of 1×10⁸ spores/m L of FDB strain was used to infect the insects.The white mycelial were observed on the surface of E.gebleri in the head,antennae,thorax tarsus,foot joints,genitalia,after insects died.4.Observing the process of B.bassiana mycelium breaking through the body wall of E.gebleri with scanning electron microscopeScanning electron microscope was used to observe the infection process and location of B.bassiana infecting E.gebleri.No mycelium was found on the body surface at 0 days after death,but mycelia appeared at the 2nd day and the 3rd day after death.And the hyphae in the 3rd day were obviously more than those in the 2nd day after death.The B.bassiana mycelium that broke out of E.gebleri were mainly concentrated in the chest,the basal fossa of the pectoral foot,the joints of the femur,the tibia of the foot,the upper lip part of the mouth organ,the antennal fossa,intersegmental membrane between somites,and genitalia.In addition,mycelium is also present near the hair.