Screening, Identification And Cultural Characteristics Of A Highly Pathogenic Strain Of Metarrhizium Against Plutella Xylostella

Diamondback moth (Plutella xylostella) is the worldwide pest, destroying cruciferous vegetables mainly. Plutella xylostella could be resistant to chemical pesticides and breed quick, the harm caused by it is serious. It's important to develop highly pathogenic fungal biopesticides against P. xylostella. In this study, the laboratory population of P. xylostella was established. The virulence of 25 strains was compared with each other to estimate the pathogenicity of Metarhizium to the 3rd larvae of P. xylostella, and one high virulent strain, CQM125, was obtained. To evaluate the effect of strain CQM125 on the control of P. xylostella and its potential application in production, the infection tests to P. xylostella were done and the main results were listed as follow:The population of P. xylostella was established in laboratory. At the constant temperature 25℃, RH 60%～80%, 14L: 10D light period in laboratory, the result showed that, the average number of eggs layed by per P. xylostella was about 40. The average number of eggs layed by single female moth could be up to 300. The mortality of larvae during phase 1 and 2 is higher. The average time of one generation is about 27 days containing egg stage 2 3d with hatching rate 97%, larvae 9 10d with the survival rate about 20%, pupal stage 3 4d with the emergence rate about 95%, adult stage 8 16d separately. The population of next generation of P. xylostella will be rise obviously. Adequate insects could be supplied for the next biotests.The virulence of 25 Metarhizium strains with different sources against P. xylostella was evaluated. Bioassay results showed that the pathogenicity of different Metarhizium strains to P. xylostella was different significantly. Metarhizium strains CQM125, CQM124, CQM117, CQM108 and CQM126 were higher pathogenic to P. xylostella than any other strains, the cumulative mortality was 84.2%, 78.9%, 74.2%, 66.9% and 64.4% respectively. Metarhizium CQM125 was the most virulent strain. For the 3rd instar larvae of P. xylostella, the cumulative mortality (8 days,20℃) was 84.2%; the LT50 (1.0×10⁸ spores·mL^-1,20℃) was 3.97 days and the LC50 (7 days,25℃) was 2.31×10⁴ spores·mL^-1. The results indicated that Metarhizium CQM125 would be a good biopesticide in application in the future.Based on the ITS sequence and morphology characteristic, CQM125 was classified into Metarhizium anisopliae. The research showed the proper basic cultural conditions of CQM125 for hypha growing and sporulation. The environmental conditions such as temperatures, illumination, pH values and the content of carbon and nitrogen were studied in details. The cultural conditional optimizing showed that PPDA is the best media for hypha growing and sporulation which contains 2% glucose and 0.5% peptone; the optimal temperature and pH were 30℃and pH 6.0.The sporulation ability of CQM125 is weak without the stimulation of light. Dark in the first 6 days and light in the last 8 days was the suitable photoperiod. Study indicated that M. anisopliae CQM125 had good adaptability to the environmental conditions, and were tolerant to high base.The extracellular protease production of Metarhizium CQM125 at 25℃was the most, and will decreased if the temperature increase or decrease. The ability of Metarhizium CQM125 to produce chitinase is weak, which can not be observed in the study.