Biocontrol potential of native entomopathogenic fungi against Phyllotreta spp. (Coleoptera: Chrysomelidae) on radish: a study of damage suppression and population dynamics.

Flea beetles (Phyllotreta spp.) have recently emerged as important pests of cruciferous crops in India. However, their incidence and management in Tamil Nadu, India remain poorly documented. This study was undertaken to assess the damage potential and explore sustainable management options in radish (Raphanus sativus), a highly susceptible, short-duration crop that experiences both foliar and root damage, often leading to increased pesticide use and residue concerns. Field surveys conducted across major radish-growing regions of Tamil Nadu revealed the occurrence of Phyllotreta striolata and P. chotanica, with P. striolata as the predominant species. Leaf and root infestation levels ranged from 0.97% - 43.38% and 8% - 52%, respectively. To develop an eco-friendly management strategy, native entomopathogenic fungi were isolated from rhizosphere soils, yielding eight isolates of Beauveria bassiana, confirmed through morphological and molecular characterization. Laboratory bioassays indicated that the isolate TNAU ENT Bb DP1 exhibited the highest virulence against adult P. striolata, with a median lethal concentration (LC₅₀) of 4.15 × 10² conidia/mL. Scanning electron microscopy confirmed successful cuticular penetration and colonization of the host. This study provides new evidence on Phyllotreta spp. infestation in radish in Tamil Nadu and highlights the potential of native Beauveria bassiana isolates for integration into sustainable pest management programs.