Assessment of Insecticidal Compatibility of Metarhizium anisopliae Isolates against Diamondback Moth (Plutella xylostella L.)

Abstract

The diamondback moth, Plutella xylostella (L.), is a serious insect pest of cruciferous crops and has developed widespread resistance to several insecticides, necessitating the development of alternative management strategies. The present investigation was undertaken to determine the compatibility of different Metarhizium anisopliae isolates with selected insecticides and to evaluate their efficacy against P. xylostella. The experiment was conducted under laboratory conditions using a two-factor completely randomised design (CRD) at the Biocontrol Research and Production Centre (BRPC), Department of Entomology, College of Agriculture, Jawaharlal Nehru Krishi Vishwa Vidyalaya (JNKVV), Jabalpur, Madhya Pradesh, during 2024–2025. Five isolates of M. anisopliae were tested in combination with spinosad, indoxacarb, fipronil and emamectin benzoate. Compatibility was assessed on the basis of radial mycelial growth, percentage inhibition, spore production and spore viability, while insecticidal activity was determined against third-instar larvae of P. xylostella. Significant variation was observed among the fungal isolates, insecticides and their interactions. ITCC-6895 exhibited the greatest radial growth (78.96 mm at 7 DAI), whereas NBAII Ma-6 showed the lowest. Emamectin benzoate exhibited the greatest compatibility with the fungal isolates and produced synergistic interactions with NBAIR Ma-56b and Ma LOCAL. Ma LOCAL recorded the highest spore viability (97.10%), while both Ma LOCAL and NBAII Ma-6 produced the highest mean spore count (1.54 × 10⁸ spores mL⁻¹). In the laboratory bioassays, all insecticides resulted in complete larval mortality after 120 h, whereas ITCC-6895 recorded the highest average mortality (94.83%) among the fungal isolates. NBAIR Ma-56b and Ma LOCAL showed highly compatible interactions with emamectin benzoate, as indicated by negative percentage inhibition values. These findings indicate that compatible combinations of M. anisopliae, particularly ITCC-6895 and Ma LOCAL, with emamectin benzoate can improve the management of P. xylostella as part of an integrated pest management programme. Overall, compatible combinations of M. anisopliae with selective insecticides demonstrated strong potential for the environmentally sound management of P. xylostella.