Studies On Application Techniques Of Entomogenous Fungi Against Spodoptera Litura

In order to find out new approaches and methods of integrate control the important agricultural insect,Spodoptera litural,and develop and utilize the resource of entomopathogenic fungi,in the present thesis,pathogenicity of different fungal species to S.litura were tested.A highly virulent entomopathogenic fungal strain,Nomuraea rileyi Nr05,was obtained,and its virulence to different instar larvae of S.litura,effects of environment factors on virulence,the synergism with other non-chemical insecticides,field trial,cultivation properties,optimal sporulation media were studied.1 Pathogenicity of different fungal species on Spodoptera lituraThe virulence test of five species of entomogenous fungi Beauveria brongniartii,Beauveria bassiana vuill,Paecilomyces fumosoroseus,Metarhizium anisopliae and Nomuraea rileyi to Spodoptera litura larvae showed Nomuraea riIeyi Nr05 obviously controlled to Spodoptera litura compared with other fungal species.Its LT₅₀value to the 4th instar larvae of Spodoptera litura was 8.99 d and adjusted accumulative mortality was 62.05%when concentration was 1×10⁸ conidia·mL^-1.2 The virulence of Nomuraea rileyi Nr05 to Spodoptera lituraThe results of pathogencity tests indicated that N.rileyi Nr05 was highly virulent to 2～5 instar larvae of S.litura,the adjusted accumulative mortality were 23.3%-98%when the range of concentrations from 5×10⁶ to 5×10⁸ conidia·mL^-1.The younger the insect was the more susceptible according to the LC₅₀values.The LC₅₀value to 2nd instar larvae was. 3.25×10⁶ conidia·mL^-1,however,the LC₅₀value to 5th instar larvae was 7.04×10⁷ conidia·mL^-1,the later was 21.7 times as the former.The pathogenicity of N.rileyi Nr05 against S.litura was examined under different temperatures in the laboratory.The results showed that S.litura had high mortality rates under the temperature ranged from 24℃to 28℃,and the most suitable temperature was 24℃.On the lower temperature,N.rileyi Nr05 still had higher virulence to S.litura,only the larvae died slowly,while the mortality decreased drastically at 32℃.The host range tested with another 11 insect species demonstrated that N.rileyi Nr05 had obviously specificity to parasitize insects.It could infect Lepidopter insects,and other order insects had not been found infected in the laboratory. 3 The synergism effect of controlling S.litura with the mixture of N.rileyi and other non-chemical insecticidesThe N.rileyi Nr05 was tested for the synergism with Autographa californica NPV, Eploxugar and Bacillus thuringiensis.Results showed that combinative application of A. caIifornica NPV and the strain resulted in a higher controlling efficacy to the 4th instar larvae of S.litura,indicating the synergism of the agents.The adjusted accumulative mortality reached 73.9%,13.7%higher than using A.caIifornica NPV and N.rileyi Nr05 alone.Its LT₅₀value decreased 1.1d and 4.7d compared with using A.californica NPV and N.rileyi alone,respectively.4 Application effects in field of N.rileyi Nr05 to the S.lituraInfectivity and control of N.rileyi Nr05 to S.litura in the fields were conducted.Sprying the spores when concentration was 1×10⁸ conidia·mL^-1in the field showed that the infectivity was high.The result on the 7th day showed the field efficacy reached 36.6%,and on the 14th day reached 44.4%.The controlling efficacy was lower than that of chlorpyrifos and A.californica NPV,but it was significantly higher than that of B.brongniartii Bjy01.Rigid cadaver infected by N.rileyi Nr05 were found in treated areas at 8th day after the spores were sprayed,and the accumulative rigid cadaver rates reached 25.4%at 14th day.Some rigid cadavers were still found in the treated areas at 30d,60d and 100d after the spores were sprayed,suggesting that the controlling efficacy of N.rileyi Nr05 to S.litura was very longer.5 The filter of the optimal sporulation media of N.rileyi Nr05The cultural characteristics of N.rileyi Nr05 was investigated.Results indicated that PPDA was suitable for N.rileyi to grow than SDAY.But the sporulation number of N.rileyi was lower than that of B.brongniartii and B.bassiana.According to the best nutrition factors for sporulation,obtained a optimal solid sporulation media by orthonormal experiment.It main components were as follows:glucose 10g/L,beef peptone 5g/L,yeast extract powder 5g/L,maltose 10g/L and vitamin B₁ 0.02g/L.The sporulation number of N.rileyi Nr05 were singificantly higher in this optimal sporulation media than in other media.The sporulation number reached 4.26×10⁸ spores/mL.