| A high virulence fungus strain of Beauveria bassiana with was isolated from infected Leptinotarsa decemlineata,the infection process and histopathological changes of potato beetle were observed.The selection of suitable mixed pesticides was used to evaluate the field efficiency based on the compatibility analysis with pesticides which common used in the control of potato pests.The main results are as follows:1.Four pathogenic fungi were isolated from Xinjiang Urumqi County Zhongliang village,Turpan Yalgel village and Wuyi Farm.By morphological and molecular biology classification,the similarity of strain TLF-Me01 with Metarhizium guizhouense was 99%,and both strain BFG-Me01 and WY-Me01 with Metarhizium anisopliaes was 99%.The similarity of strain N DBJJ-BFG with Beauveria bassiana reached 99%.2.Results showed that 4 strains of fungi have strong ability to infect potato beetle larvae.Pathogenicity of NDBJJ-BFG strain is the strongest and the cumulative mortality for potato beetle larvae was between 88.39%~100%,and for pupae and adults was between 83.89%~93.33% after 9 days of inoculation.The LT50 of 1 to 4 instars larvae were 3.7 d,5.9 d,6.2 d and 6.8 d respectivelyat the concentration of 1×108 spore/m L.3.The infection process and histopathology of B.bassiana strain NDBJJ-BFG infection of the Colorado potato beetle using scanning electron microscopy and hematoxylin-eosin staining of tissue sections.Results show that the fungus penetrated the insect epidermis through germ tubes and appressoria after spraying the larvae with conidial suspensions.The conidia began to germinate after 24 hours and invade the epidermis.After 48 hours,the conidia invaded the larvae with germ tubes and began to enter the haemocoel.By 72 hours,hyphae had covered the host surface and had colonized the body cavity.The dermal layer was dissolved,muscle tissues were ruptured and adipose tissue was removed.The mycelium had damaged the intestinal wall muscles,and invaded into intestinal wall and midfield cells resulting in cell separation and tracheal deformation.After 96 hours of inoculation,the internal structure of the larvae was destroyed.After 96 hours,a large number of hyphae penetrated the body wall,and a large number of conidia were produced in the mycelium.After 96 hours of inoculation a large number of conidia formed.4.Results of pesticide compatibility test show that,70% imidacloprid WG had little effect on the strains,and 20% Cymbidium EC and the 4.5% high effective cypermethrin microemulsion could be mixed,at very low concentration.Whereas 3.2% Avermectin EC and 40% phoxim EC as well as 80% carbendazim WP stronginhibited the germination and sporulation of spores 41% glyphosate had no significant inhibition on spore germination,but its high concentrationinhibited the colony growth and sporulation.5.Field experiment showed that the best control effect of Beauveria bassiana against larvae was obtained after 12 d of treatment,the field efficacies were 91%,80% and 68%,respectively,with the concentrations of 1×109 spores/m L?1×107 spores/m L and 1×105 spores/m L whereas the best control effect on adults was obtained after 9d of treatment,and the field efficacies were 58%,48% and 42%,respectively.The control effect on larvae was 92% and 95%,on adults were 80% and 85%,respectively,for the treatments of 1×107 spores/m L + imidacloprid 15000 times and imidacloprid 3000 times.It suggested that low concentration of imidacloprid increased the infection ability of Beauveria bassiana NDBJJ-BFG,and the combined use showed out excellent prospect in the control of Leptinotarsa decemlineata(Say). |
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