Pathogenicity and ultramicroscopic analysis of green muscardine fungus, Metarhizium anisopliae, infecting the tomato fruit borer, Helicoverpa armigera.

The polyphagous insect Helicoverpa armigera is a devastating pest known to develop resistance to insecticides quickly. In the search for alternatives, the entomopathogenic fungus Metarhizium anisopliae has been found to be an eco-friendly component of integrated pest management for lepidopteran insects all over the world. On tomatoes, this pest devours both the leaves and the fruits. The present investigation was carried out to identify effective M. anisopliae strains against H. armigera through ultramicroscopic investigations. The fungal strains sourced from soil and Spodoptera frugiperda cadavers were subjected to molecular and morphological characterization, confirming their identity as M. anisopliae. Of the 10 M. anisopliae strains, ICAR SBI Ma 08 and ICAR SBI Ma 01 ranked first and second in efficacy against H. armigera second and fourth instars, respectively. The order of efficacy of other strains against H. armigera was ICAR SBI Ma 69 > ICAR SBI Ma 44 > ICAR SBI Ma 07 > ICAR SBI Ma 05 > ICAR SBI Ma 172 > ICAR SBI Ma 03 > ICAR SBI Ma 46 > ICAR SBI Ma 04. Ultramicroscopic examinations found the growth of mycelia in the natural openings of the larva, such as the spiracles, thorax, legs, and setal alveoli, within 168 h. The tested strains demonstrated greater effectiveness against the second instar compared with the fourth instar, suggesting that the most potent strain, ICAR SBI Ma 08, can effectively manage the early instars.