Screening of Native Beauveria Isolates for Virulence Against Rhizotrogus spp. (Coleoptera: Scarabaeidae) Larvae in Soil

Abstract

Rhizotrogus spp. larvae (Coleoptera: Scarabaeidae) are destructive soil-dwelling pests that cause significant damage to agricultural crops by feeding on plant roots, resulting in reduced plant vigor and considerable yield losses. Biological control using entomopathogenic fungi has emerged as an environmentally sustainable alternative to chemical insecticides for the management of soil insect pests. The present study aimed to screen native isolates of Beauveria spp. for their virulence against Rhizotrogus larvae under soil conditions. Native fungal isolates were collected from different agroecological regions and cultured under laboratory conditions for morphological and molecular identification. Bioassays were conducted by exposing larvae to different concentrations of fungal conidia in treated soil, and larval mortality was recorded over a defined experimental period. Parameters including mortality percentage, median lethal time (LT50), fungal colonization, and mycosis development were evaluated to determine the pathogenic potential of each isolate. The results revealed significant variability in virulence among the tested Beauveria isolates. Several native isolates exhibited high pathogenicity, causing substantial larval mortality and rapid infection under controlled soil conditions. Infected larvae showed characteristic symptoms of fungal infection, including reduced mobility, discoloration, and external fungal growth. Molecular characterization confirmed that the most effective isolates belonged to the genus Beauveria, with close similarity to previously reported entomopathogenic strains. The study demonstrated the potential of native Beauveria isolates as effective biological control agents against Rhizotrogus larvae. The identification of highly virulent indigenous isolates provides an important foundation for the development of eco-friendly biopesticides and integrated pest management strategies. The application of native entomopathogenic fungi may therefore contribute to sustainable crop protection and reduced dependence on synthetic chemical pesticides.