First report on the enzymatic and immune response of Metarhizium majus bag formulated conidia against Spodoptera frugiperda: An ecofriendly microbial insecticide

Vivekanandhan Perumal; Swathy Kannan; Lucy Alford; Sarayut Pittarate; Ruchika Geedi; Dilipan Elangovan; Ramachandran Marimuthu; Patcharin Krutmuang

doi:10.3389/fmicb.2023.1104079

First report on the enzymatic and immune response of Metarhizium majus bag formulated conidia against Spodoptera frugiperda: An ecofriendly microbial insecticide

Front Microbiol. 2023 Mar 2:14:1104079. doi: 10.3389/fmicb.2023.1104079. eCollection 2023.

Authors

Vivekanandhan Perumal^{1

2}, Swathy Kannan¹, Lucy Alford³, Sarayut Pittarate¹, Ruchika Geedi⁴, Dilipan Elangovan², Ramachandran Marimuthu⁵, Patcharin Krutmuang^{1

6}

Affiliations

¹ Department of Entomology and Plant Pathology, Faculty of Agriculture, Chiang Mai University, Chiang Mai, Thailand.
² Department of Physiology, Saveetha Dental College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, Tamil Nadu, India.
³ School of Biological Sciences, University of Bristol, Bristol, United Kingdom.
⁴ Geedi-Horticultural Insects Research Laboratory, USDA- Agricultural Research Services, Wooster, OH, United States.
⁵ Department of Botany, School of Life Sciences, Periyar University, Salem, Tamil Nadu, India.
⁶ Innovative Agriculture Research Center, Faculty of Agriculture, Chiang Mai University, Chiang Mai, Thailand.

Abstract

Entomopathogenic fungi from microbial sources are a powerful tool for combating insecticide resistance in insect pests. The purpose of the current study was to isolate, identify, and evaluate bag-formulated entomopathogenic fungal conidial virulence against insect pests. We further investigated the enzymatic responses induced by the entomopathogenic fungi as well as the effect on a non-target species. Entomopathogenic fungi were isolated from the Palamalai Hills, India, using the insect bait method, and the Metarhizium majus (MK418990.1) entomopathogen was identified using biotechnological techniques (genomic DNA isolation and 18S rDNA amplification). Bag-formulated fungal conidial efficacy (2.5 × 10³, 2.5 × 10⁴, 2.5 × 10⁵, 2.5 × 10⁶, and 2.5 × 10⁷ conidia/ml) was evaluated against third instar larvae of Spodoptera frugiperda at 3, 6, 9, and 12 days of treatment, and acid and alkaline phosphatases, catalase, and superoxide dismutase enzymatic responses were evaluated at 3 days post-treatment. After 12 days of treatment, non-target assays on the earthworm Eudrilus eugeniae were performed using an artificial soil assay. Results of the bag formulated fungal conidial treatment showed that S. frugiperda had high susceptibility rates at higher concentrations (2.5 × 10⁷ conidia/ml) of M. majus. Lower concentration of 2.5 × 10³ conidia/ml caused 68.6% mortality, while 2.5 × 10⁷ conidia/ml caused 100% mortality at 9 days post treatment. Investigation into enzymatic responses revealed that at 3 days post M. majus conidia exposure (2.5 × 10³ conidia/ml), insect enzyme levels had significantly changed, with acid and alkaline phosphatases, and catalase enzymes significantly reduced and superoxide dismutase enzymes significantly raised relative to the control. After 12 days of treatment, no sublethal effects of M. majus conidia were observed on E. eugeniae, with no observed damage to gut tissues including lumen and epithelial cells, the nucleus, setae, coelom, mitochondria, and muscles. This study offers support for the use of fungal conidia in the target-specific control of insect pests.

Keywords: Eudrilus eugeniae; Metarhizium majus; Spodoptera frugiperda; antioxidant enzyme; microbial insecticide; natural insecticide.