Study on the virulence of Metarhizium anisopliae against Spodoptera frugiperda (J. E. Smith, 1797)

This study examined the impact of Metarhizium anisopliae (Hypocreales: Clavicipitaceae) conidia on the eggs, larvae, pupae, and adults of Spodoptera frugiperda. The results showed that eggs, larvae, pupae, and adults exhibited mortality rates that were dependent on the dose. An increased amount of conidia (1.5 × 109 conidia/mL) was found to be toxic to larvae, pupae, and adults after 9 days of treatment, resulting in a 100% mortality rate in eggs, 98% in larvae, 76% in pupae, and 85% in adults. A study using earthworms as bioindicators found that after 3 days of exposure, M. anisopliae conidia did not cause any harmful effects on the earthworms. In contrast, the chemical treatment (positive control) resulted in 100% mortality at a concentration of 40 ppm. Histopathological studies showed that earthworm gut tissues treated with fungal conidia did not show significant differences compared with those of the negative control. The gut tissues of earthworms treated with monocrotophos exhibited significant damage, and notable differences were observed in the chemical treatment. The treatments with 70 and 100 µg/mL solutions of Eudrilus eugeniae epidermal mucus showed no fungal growth. An analysis of the enzymes at a biochemical level revealed a decrease in the levels of acetylcholinesterase, α-carboxylesterase, and β-carboxylesterase in S. frugiperda larvae after exposure to fungal conidia. This study found that M. anisopliae is effective against S. frugiperda, highlighting the potential of this entomopathogenic fungus in controlling this agricultural insect pest.