High Virulence of Mexican Entomopathogenic Fungi Against Fall Armyworm, (Lepidoptera: Noctuidae)

摘要

Fourteen fungal entomopathogenic strains were isolated from soil samples and infected field-collected fall armyworm larvae, in Guanajuato, Mexico. Isolates were identified by morphology and internal transcribed spacers sequencing. Isolates Ma22, Ma41, and Mr8 showed 99% identity with reference strains (RS) of Metarhizium anisopliae. Isolates Bb9, Bb19, Bb21, Bb40, Bb27, Bb23, and Bb39 showed identity between 99 and 100% with RS of Beauveria bassiana. Isolates Nr1, Nr2, Nr3, and Nr4 showed identity between 98 and 100% with RS of Nomuraea rileyi. Qualitative selection used one concentration (1 x 10(8) conidia/ml) on fall armyworm eggs and neonate larvae. Strains Ma22, Ma41, and Mr8 showed 100%, and strains Bb39, Bb23, Bb9, Bb40, Bb19, and Bb21 showed 92, 89.2, 87.6, 82.8, 58, and 38% egg mortality, respectively. Bioassays on neonate larvae showed 100% mortality with strains Ma22, Ma41, Mr8, and Bb9. Strains Bb39, Bb19, Bb27, Bb23, Bb21, and Bb40 showed 74, 60, 54, 53, 28, and 19% mortality, respectively. Bioassay estimated LC(50)s for strains Ma41 at 7.4 x 10(4), Mr8 at 8.9 x 10(4), and Ma22 at 10 x 10(4) conidia/ml, on fall armyworm eggs. LC(50)s on neonate larvae were estimated at 2.8 x 10(5), 16 x 10(5), 26 x 10(5), and 36 x 10(5) conidia/ml for strains Ma41, Bb9, Ma22, and Mr8, respectively. Virulence genes mad1 and mad2 were found in Mr8, Ma22, and Ma41, whereas the gen gmact was found only in the strain Ma22. Genes hyd1 and hyd2 were identified in Bb9, Bb19, Bb21, and Bb27. No correlation was observed between the virulence gene detection and the estimated LC(50)s. Strain Ma41 showed the highest potential to be developed as a bioinsecticide.