Molecular, morphological and pathogenic characterization of six strains of Metarhizium spp. (Deuteromycotina: Hyphomycetes) for the control of Aegorhinus superciliosus (Coleoptera: Curculionidae)

María Sepúlveda1*, Marisol Vargas2, Macarena Gerding2, Ricardo Ceballos1, Pía Oyarzúa2
Aegorhinus superciliosus is an important pest on blueberry (Vaccinium corymbosum L.) and other fruit trees. The use of entomopathogenic fungi as Metarhizium spp. has been evaluated for the control of this insect, but variability has been observed among different strains of this microorganism. The aim of this study was to characterize six promising strains of Metarhizium spp. for the control of A. superciliosus. The studied strains were QuM173c, Qu-M363, Qu-M171a, Qu-M156a, Qu-M421, and Qu-M430, all of which belonged to the Chilean Collection of Microbial Genetic Resources (ChCMGR) of the Instituto de Investigaciones Agropecuarias (INIA), Chile. Molecular characterization was made by sequencing the ITS region (Internal Transcribed Spacers, ITS-5.8S rDNA). The morphology of the conidia was evaluated through scanning electron microscopy and the radial colony growth was evaluated in potato dextrose agar (PDA), Sabouraud dextrose agar (SDA), agar enriched with larvae of Galleria mellonella (Lepidoptera: Pyralidae) (GA), and agar enriched with adults of A. superciliosus (AA). Pathogenicity was studied based on the mortality of adults of A. superciliosus inoculated with conidia. Sequencing of the ITS-5.8S rDNA region indicates that the strains belong to the clade of M. anisopliae var. anisopliae, except for Qu-M171a, which was identified as M. anisopliae var. lepidiotum. Conidia average length for the six strains was 5.09 µm and average conidia width was 1.92 µm. Radial colony growth differences were observed between strains (p < 0.01) and between the different growth media that were used (p < 0.01). The strains exhibited the highest colony growth in the GA medium, while in the AA medium they showed the lowest (p < 0.01). Pathogenicity tests show that strain Qu-M430 reached a 90% mortality rate (p < 0.01). Results show that there is variability between the studied strains, which is expressed in their morphology, molecular characteristics and pathogenicity towards A. superciliosus.
Keywords: Aegorhinus superciliosus, biological control, entomopathogen, Metarhizium anisopliae, radial growth, ITS regions (Internal Transcribed Spacers)
1Instituto de Investigaciones Agropecuarias, INIA Quilamapu, Av. Vicente Méndez 515, Chillán, Chile. *Corresponding author (mesepulve@inia.cl).
2Universidad de Concepción, Facultad de Agronomía. Av. Vicente Méndez 595, Chillán, Chile.