Biological Characteristics Of A High Virulent Isolate Of Metarhizium Anisopliae And Histopathology Of Infected Anoplophora Glabripennis Larvae

Metarhizium anisopliae,which belongs to Deuteromycetes,Moniliales,Tuberculariaceae, is a species of broad-spectrum insecticidal fungi.It can parasitize more than 200 kinds of insects belonging to 8 Orders,30 Families,as well as mites and nematodes. Metarhizium anisopliae,a fungus that infects insects as a biological control agent,has been successfully used in many agricultural and forest pests.This paper deals with the basal biological characteristics,the pathogenicity against Anoplophora glabripennis and factors affecting the pathogenicity,infection mode of the host to the pathogen,the pathological changes of A.glabripennis larvae infected by MSO1,a high virulent isolate MSO1 to A. glabripennis larvae which was screened from the isolates collected from the soil using the "Tenebrio molitor Bait Method" and compared with the commercial strains.The results are as follows:1.Isolation,culture,screening of the high virulent isolate.The pathogenic fungus strain was isolated and cultivated by PPDA medium.Eight isolates of Metarhizium anisopliae were isolated from different 16 kinds of soils using the "Tenebrio molitor Bait Method".The isolation rate was 50%and the highest infection rate was 52.40%in the Poplar woodland.The pathogenicity of different strains to A. glabripennis larvae was tested,and the comparison of pathogenicity against A. glabripennis larvae between the saled and the isolated was research.The result showed that MSO1 was the highest virulent.The correct mortality was up to 100%,and the infection rate was 83.33%.LT₅₀ was 2.69d,and LC₅₀ on the A glabripennis larvae was determined to be 1.68×l0⁶mL^-1.Compared with the commercial strain,the death rate of strain MSO1 was up to 100%,the infection rate was 90.40%,and LT₅₀ was 5.25d,with the faster death speed.Therefore,strain MSO1 would be as the target strain in the subsequent study of biological characteristics and the alternative strains.2.The study of biological characteristics of strains MS01.The culture medium,temperature,humidity,photoperiod and different time exposed to UV light were the most important dominant factors of the growth and pathogenicity to strains MS01.The most suitable media for the mycelia growth and conidia production of MS01 was PPDA,the optimal relatively humidity was 100%.The optimal temperature for the nutrient growth was 26℃and the conidia production was more.While the optimal temperature for the conidia production and germination was 28℃,and the nutrient growth was faster.The optimal photoperiod for the conidia production was dark in the first 7 days and light in the last 7days,and alternate light was beneficial to the formation of spores.The effect of different time exposed to UV light on strains MSO1 was insignificant.With the increasing of UV exposure time,the conidia production was lower and lower.Conidia in the nutrient liquid of 2%glucose +1.5%peptone germinated rapidly,with the highest germination rate.3.The study of pathogenicity to A.glabripennis and factors affecting the pathogenicity.The strains MSO1 can not infect the eggs of A.glabripennis.While the effects of strains MSO1 infection on adult A.glabripennis feeding,oviposition,egg hatching and subsequent survival of offspring by adult A.glabripennis was significant.Adult A. glabripennis infected with MSO1 reduced both feeding and fecundity,and the higher the concentration,the lower the rate.The accumulated survival rate lowered through horizontal transmission of MSO1 to offspring.At 26℃and RH 100%,the pathogenicity reached the highest.4.The symptom and histopathological study of A.glabripennis larvae Infected with MSO1.There were some changes in both color and morphology on the A.glabripennis larvae infected with MSO1.Paraffin sections showed the spores of MSO1 attached to the cuticle of A.glabripennis larvae at 24h post inoculation(hpi).At 36 hpi,the conidium germinated and penetrated through the cuticle.After 48h,the endocuticle were disintegrated,the germ tubes had passed through the epithelial layers into the body cavity and multiplied,and invaded the tissues nearby the penetration point,such as the fat body,muscle,trachea tissue,malpighian tubule,alimentary canal,etc.Infected larvae were dead and most tissues and organs were infected and disintegrated with the multiplication of the mycelium by 3 d. The hyphae emerged through the cuticle and formed hyphal layer on the surface of the dead insect and the conidium emerged at 5 d post inoculation(dpi).