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

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.

Entomopathogenic fungi based microbial insecticides and their physiological and biochemical effects on Spodoptera frugiperda (J.E. Smith)

“…The most significant decrease in β-carboxylesterase activity occurred after a treatment period of three days. These results support previously published studies showing that entomopathogenic fungal conidia and secondary metabolites reduce the acetylcholinesterase, α- and β-carboxylesterase enzyme levels in Spodoptera litura and Spodoptera frudiperda ( Karthi et al., 2018 ; Karthi et al., 2019 ; Perumal et al., 2023a ; Perumal et al., 2023b ).…”

“…Here, M. anisopliae conidia resulted in 97% mortality in the second instar, 87% in the third instar, 77% in the fourth instar, and 72% in the fifth instar larvae at nine days post-treatment. Insect larvae in their early instar stages are more sensitive to fungal infection than larvae in later instars as a result of the immune and physiological systems still developing ( Perumal et al., 2023a ; Perumal et al., 2023b ). Similar to our study, the entomopathogenic fungus, M. anisopliae has been previously shown to cause 100% mortality rates in S. frugiperda under laboratory trials ( Ramos et al., 2020 ).…”

Biocontrol effects of chemical molecules derived from Beauveria bassiana against larvae of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

“…For 15 days, plastic containers were observed twice daily. After collecting the larval cadavers and sterilizing them for 2–3 min with 70% ethanol, the sterile cadavers were transferred to Petri plates (90 mm × 15 mm) containing pre-prepared potato dextrose agar medium PDA (HiMedia, India) ( Perumal et al, 2023a ). Plates were kept at a relative humidity of 85% and a temperature of 26 ± 2°C for 7 to 10 days.…”

“…When various chemical insecticides, such as permethrin, cypermethrin, monocrotophos, and malathion, are repeatedly used, insects develop resistance to these chemical pesticides ( Metcalf, 1989 ; Gahukar and Kishore, 1995 ; Vivekanandhan et al, 2021 ). As a result, various methods of controlling insects using secondary metabolites from plants, bacteria, and fungi have shown greater efficacy ( Balumahendhiran et al, 2019 ; Logeswaran et al, 2019 ; Pratheeba et al, 2019 ; Vivekanandhan et al, 2022a , b ; Chinnasamy et al, 2023 ; Kannan et al, 2023 ; Krutmuang et al, 2023 ; Perumal et al, 2023a , b , c ).…”

Determination of internal controls for quantitative gene expression of Spodoptera litura under microbial pesticide stress

“…Of all biopesticides, microbial pesticides are becoming increasingly more important and have gained significant popularity because they are safe and environmentally friendly 20 , 21 . The most widely used microbial pesticides are strains of Bacillus , Metarhizium and Empedobacter , these have all been demonstrated to be effective against various Lepidoptera pests 22 – 28 . However, in a manner similar to that of chemical control methods, some target herbivores, including S. litura , have developed resistance to microbial pesticides, including B. thuringiensis 29 – 33 .…”