Pathogenicity of microencapsulated insecticide from Beauveria bassiana and Metarhizium anisopliae against tobacco budworm, Heliothis virescens (Fabricius)

Pathogenicity of microencapsulated spores of Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metsch) Sorokin at a dose of 1 × 10⁸ spores per milliliter were used against tobacco budworm, Heliothis virescens (Fabricius) (Lepidoptera: Noctuidae). Toxicity of non-microencapsulated spores at the same dose was also assessed. Bovine gelatin was used as a matrix to produce microcapsules by the spray-drying technique with an inlet temperature of 85°C and an outlet temperature of 33°C in the spray dryer process. Scanning electron microcopy was used to assist with measuring the microcapsule size and determining spore shape. Spore viability and moisture were also evaluated. Both fungal formulations were applied by immersing first-instar tobacco budworm larvae for 30 seconds. The number of larvae that died was recorded 48 hours post inoculation. Microcapsules were <20 m. Spore viability was 16.0 ± 0.7% for B. bassiana and 13.2 ± 0.8% for M. anisopliae. Moisture contents of the fungi were 9.6 ± 3.9 and 9.3 ± 3.8%. Percentages of larvae killed were 33.3 ± 5.7 and 56.8 ± 5.8% for B. bassiana and M. anisopliae, respectively. The median lethal times were 60.0 ± 16.8 hours post inoculation for M. anisopliae and 85.9 ± 15.4 for B. bassiana non-microencapsulated spores, while the same microencapsulated fungi were 67.8 ± 15.3 and 72.0 ± 16.0 hours post inoculation. Spores of both fungi survived the spray-drying procedure (at 85 and 33°C) and were able to infect first-instar tobacco budworm larvae under laboratory conditions.