| The tobacco beetle is highly adaptable and has a wide range of feeding characteristics,which harms and contaminates tobacco products at all stages of processing,and its larvae cause tobacco leaf perforation and fragmentation by feeding on tobacco leaves,which seriously affects the quality of tobacco leaves.Today,the control of tobacco beetle mainly relies on chemical fumigation treatment,but with the gradual increase in chemical resistance of tobacco beetle,its fumigation control effect is greatly reduced.Chemical fumigation is very likely to cause environmental pollution.Therefore,there is an urgent need to find environmentally friendly and less resistant control agents to replace the environmental pollution and food safety problems caused by chemical fumigation.At present,insect pathogenic fungi with broad-spectrum insecticidal effects,such as Beauveria bassiana,Metarhizium anisopliae and Verticilliu mfungus,have been commercialized at home and abroad,and have achieved more obvious results in the control of important agricultural and forestry pests.The effect of these fungi in the control of important agricultural and forestry pests has been more obvious.However,there are few reports on the control of tobacco beetle by entomopathogenic fungi at home and abroad.In this study,a strain of B bassiana,Bb05,was isolated from a field insect that naturally developed the disease,and its virulence and growth status were compared with other strains of entomopathogenic fungi kept in the laboratory to evaluate its potential application in green control of tobacco beetle.In order to investigate the mechanism of infestation of Bb05 on tobacco nail,the virulence of Bb05 was determined and the process of infestation of tobacco nail was observed using various microscopes.The main results of this study are as follows.1.Screening of highly virulent entomopathogenic fungi against tobacco nail:10strains of entomopathogenic fungi were inoculated on SDAY medium,and the morphology of the 10 strains cultured was basically similar,among which the growth rate and spore production of strain Bb05 and strain Bbr81 were better,with colony diameters of 50.37 mm and 49.10 mm at 15 d of inoculation,and spore production of6.98×107 and 7.13×The highest pathogenicity was found in strain Bb05,with77.78%mortality rate and 7.60 d LT50 after 10 d of treatment,which was smaller than other strains,followed by strain Bbr81,with 74.44%mortality rate and 8.18 d LT50after 10 d of treatment,which was significantly higher than other strains.The LC50 of strain Bb05 was 2.88×106 spores/m L and that of strain Bbr81 was 4.23×106spores/m L.2.The virulence of Fungal strains Bb05 on different forms of Lasioderma serricorne and the infestation process were observed:the virulence of Fungal strains Bb05 on different forms of tobacco beetle in descending order was adult tobacco beetle>2nd instar larvae of tobacco beetle>pupae of L.serricorne.After inoculation with the spore suspension of Fungal strain Bb05,the larvae started to move slowly on the second day,and then mycelium appeared on the foot,head and stomata on the side of the body.The larvae gradually changed to light purple on the 4th day and died of water loss on the 9th day,and the white mycelium covered the surface of the larvae.It was observed under scanning electron microscope that conidia were attached to the depressions on the body surface of tobacco beetle at 1 d of inoculation,and the secreted material adhered to and dissolved the epidermis;at 3 d of inoculation,spores started to sprout and grow on the body surface and penetrated the body wall to invade the body of tobacco beetle;at 9 d of inoculation,mycelium penetrated the body surface to cover the whole insect and produced a large number of conidia;at 10 d of inoculation,mycelium and spores were produced on the body surface of tobacco beetle and expanded outward.3.Combined application of Fungal strains Bb05 and ethyl polymicrobial on tobacco beetle virulence experiments:different concentrations of ethyl polymicrobial（diluted 500 times,1000 times,2000 times,4000 times,8000 times）and Fungal strains Bb05（5 mm diameter disc）for antagonistic culture,in the 6th day of culture,adding ethyl polymicrobial 8000 times solution on strain Bb05 The inhibition rate of strain Bb05 colonies was 0.00%at the 6th day of incubation and 0.69%at the 9th day of incubation,which was significantly lower than the other treatments.Ethyl polymicrobial was used alone and in combination with a suspension of Fungal strains Bb05 spores（1.0×108 spores/m L）to control tobacco beetle 2nd instar larvae.The results showed that the lethality of 7 d of ethyl polymicrobial 8000 and Fungal strains strain Bb05 spore suspension（1.0×108 spores/m L）was 100.00%and 35.56%,respectively,while an equal volume mixture of ethyl polymicrobial 8000 and Fungal strains Bb05 spore suspension（1.0×108 spores/m L）at 5th The mortality rate of L.serricorne was up to 100.00%at d,and the lowest LT50 was 2.06 d.The synergistic effect between ethyl polymicrobial and Bradyrhizobium strain Bb05 was demonstrated.4.Combined application of C.albicans Bb05 and L.serricorne traps for the control of adult tobacco beetle under live storage conditions:The L.serricorne trap cores and non-woven fabric with C.albicans Bb05 spore suspension（1.0×108spores/m L）were packed into modified L.serricorne traps and placed above the bales in the tobacco warehouse.The traps were placed for 10 d.The number of L.serricorne in the traps was surveyed daily,and the number of adult L.serricorne trapped was collected and recorded as deaths.The results showed that the application of strain Bb05 spore suspension（1.0×108 spores/m L）for 12 d resulted in 76.89%control of L.serricorne adults,which tentatively demonstrated the possible application of the entomopathogenic fungus in storage conditions. |
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