Simplicillium and Leptobacillium are entomopathogenic fungal genera frequently associated with arthropods in tropical ecosystems and considered promising candidates for biological pest control. However, the diversity of these genera in tropical regions, particularly in Malaysia, has not been systematically investigated in the context of their taxonomy and phylogenetic relationships. This study aimed to investigate the taxonomic diversity and phylogenetic relationship of Simplicillium and Leptobacillium using integrated morphological and molecular analyses. During a survey of entomopathogenic fungi conducted in Malaysia from 2022–2023, parasitized insects were collected, including spiders and wasps infected by entomopathogenic fungi. Phylogenetic analyses were performed using concatenated datasets of the internal transcribed spacer (ITS) and translation elongation factor 1‐alpha ( TEF1‐α ) gene to construct phylogenetic trees. The study identified one novel species, Leptobacillium geminatum sp. nov., isolated from a spider. In addition, five species are reported here as new records for Malaysia: S. formicae , L. leptobactrum. symbioticum, and L. coffeanum isolated from spiders and S. puwenense , isolated from a wasp. Morphological characteristics together with molecular phylogenetic evidence supported the taxonomic placement of these taxa. These findings represent the first comprehensive documentation of Simplicillium and Leptobacillium species from Malaysia, significantly expanding the known diversity and geographical distribution of these entomopathogenic fungi in Southeast Asia.
Shahbaz et al. (2026) studied this question.