Dynamics of natural infection of white grub larvae by Beauveria and Metarhizium in maize crops from Mexico

Abstract

ABSTRACT White grubs in the genus Phyllophaga are serious pest affecting many crops including maize. Entomopathogenic fungi are among the most promising biological control agents against white grubs. We hypothesised that there would be a temporal and/or spatial succession of entomopathogenic fungal species present in populations of Phyllophaga larvae throughout a maize crop season. Therefore, in order to assess the taxonomic and genetic diversity of fungal pathogens, we undertook a two-year field study sampling Phyllophaga larvae on maize crops at 11 localities from Mexico on a monthly basis, from August to December in 2019 and July to November in 2020. Entomopathogenic fungi infecting Phyllophaga larvae were isolated and identified to species level based on partial Bloc and Elongation Factor 1-α sequences. Genetic variation in the most abundant species was assessed by AMOVA and Haplotype network analyses. In total, we collected 3198 Phyllophaga larvae. Four Phyllophaga species were identified: Phyllophaga ravida Blanchard, P. polyphylla Bates, P. integriceps Mocer and P. vetula Horn. From the total larvae collected, 124 were infected by Beauveria and 15 by Metarhizium. Phylogenetic analysis revealed that the majority of the isolates were from the species Beauveria pseudobassiana and Metarhizium pingshaense. The Analysis of Molecular Variance (AMOVA) showed that neither year of collection nor sampling locality had a significant effect on genetic variation among B. pseudobassina isolates. However, haplotype network analysis identified two separate networks, each containing mostly isolates from 2019 and 2020 respectively. We discuss the potential effect of abiotic factors on infection levels found in Phyllophaga larvae.