Partial ecological niche partitioning between Beauveria brongniartii and Beauveria pseudobassiana entomopathogens at Melolontha melolontha infested sites

Authors: PEDRAZZINI, CHIARA - Agroscope; Rehner, Stephen; STEWART-SMITH, FIONA - Agroscope; BOSCHI, SARAH - University Of Siena; WIDMER, FRANCO - Agroscope; ENKERLI, JURG - Agroscope

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2025
Publication Date: 5/14/2025
Citation: Pedrazzini, C., Rehner, S.A., Stewart-Smith, F., Boschi, S., Widmer, F., Enkerli, J. 2025. Partial ecological niche partitioning between Beauveria brongniartii and Beauveria pseudobassiana entomopathogens at Melolontha melolontha infested sites. Journal of Invertebrate Pathology. 211:108356. https://doi.org/10.1016/j.jip.2025.108356.
DOI: https://doi.org/10.1016/j.jip.2025.108356

Interpretive Summary: Some fungi can be used to suppress outbreaks of insect plant pests. One such pathogenic beetle can be infected by two different species of fungi. To determine if there was a consistent difference in the distribution of the soil-inhabiting fungus and the above-ground fungus typically found on beetles in the tree canopies, DNA sequences were used. Both species are pathogenic to the adult beetles, with the soil-inhabiting fungus causing the highest mortality rates. Nevertheless, pathogenicity observed with the above-ground fungus suggests this insect pathogenic fungus also holds potential as a complementary biological control. The results of this study will help insect mycologists, fungal ecologists and pest management specialists using fungi for insect biological control.

Technical Abstract: Beauveria brongniartii specifically infects the insect pest Melolontha melolontha and is commonly isolated from soil and larvae. Since 1990, it has been used commercially as a biological control agent (BCA) against the larvae. Recent research revealed that B. pseudobassiana was the most frequently isolated pathogen from adult beetles collected aboveground across 35 alpine sites. This led us to hypothesize that B. pseudobassiana primarily infects adults aboveground, while B. brongniartii mainly targets larvae in soil. To explore this, we investigated the occurrence and distribution of both species at two M. melolontha-infested sites in Switzerland using phylogenetic analyses and microsatellite markers. Species-specific microsatellite markers were developed for B. pseudobassiana, and existing markers were applied to B. brongniartii. From 399 Beauveria spp. isolates collected from adult beetles, soil, grassland plants, and tree leaves, 362 were identified as B. brongniartii, which was present in all sources except tree leaves, and 37 as B. pseudobassiana, found in all sources including tree leaves, except soil. The most common B. brongniartii multilocus genotypes (MLGs) were those of the BCA BIPESCO 2 and BIPESCO 4, likely a result of previous BCA applications. One B. pseudobassiana SSR-based MLG was found in both tree leaves and M. melolontha in the tree canopy. Additionally, B. pseudobassiana established from the phylloplane exhibited pathogenicity against M. melolontha adults, suggesting a possible aboveground infection. To further investigate B. pseudobassiana intraspecific diversity, 13 unique Bloc haplotypes from this study were combined with 58 GenBank sequences and 18 genome accessions of B. pseudobassiana in a phylogenetic analysis using Bloc and Midasin I ATPase sequences, that suggest the species comprises a cryptic complex with distinct genetic clusters. Overall, this study shows B. brongniartii predominates in soil, while B. pseudobassiana occurs in the phylloplane, suggesting its potential as a complementary biological control for adult beetles aboveground.