Pathogenicity of Metarhizium rileyi (Hypocreales: Clavicipitaceae) against Tenebrio molitor (Coleoptera: Tenebrionidae)

Abstract

Tenebrio molitor L., also known as the mealworm, is a polyphagous insect pest that infests various stored grains worldwide. Both the adult and larval stages can cause significant damage to stored grains. The present study focused on isolating entomopathogenic fungi from an infected larval cadaver under environmental conditions. Fungal pathogenicity was tested on T. molitor larvae and pupae for 12 days. Entomopathogenic fungi were identified using biotechnological methods based on their morphology and the sequence of their nuclear ribosomal internal transcribed spacer (ITS). The results of the insecticidal activity indicate that the virulence of fungi varies between the larval and pupal stages. In comparison to the larval stage, the pupal stage is highly susceptible to Metarhizium rileyi, exhibiting 100% mortality rates after 12 days (lethal concentration 50 [LC50] = 7.8 × 106 and lethal concentration 90 (LC90) = 2.1 × 1013 conidia/mL), whereas larvae showed 92% mortality rates at 12 days posttreatment (LC50 = 1.0 × 106 and LC90 = 3.0 × 109 conidia/mL). The enzymatic analyses revealed a significant increase in the levels of the insect enzymes superoxide dismutase (4.76–10.5 mg−1) and glutathione S‐transferase (0.46–6.53 mg−1) 3 days after exposure to M. rileyi conidia (1.5 × 105 conidia/mL) compared to the control group. The findings clearly show that M. rileyi is an environmentally friendly and effective microbial agent for controlling the larvae and pupae of T. molitor.

Survival dynamics of stick insect and the impact of environmental factors on natural fungal infection during the rainy season

“…Entomopathogenic fungi have emerged as highly promising alternative biocontrol agents to chemical insecticides ( Erler and Ates, 2015 ; Perumal et al, 2023 ; Vivekanandhan et al, 2023 ; Perumal et al, 2024a , b ). Metarhizium and Beauveria species are two main generalist entomopathogenic fungi widely employed in pest control across various insect species, including agricultural pests ( Mascarin and Jaronski, 2016 ; Peng et al, 2021 ; Krutmuang et al, 2023 ; Vivekanandhan et al, 2024 ; Perumal et al, 2024a , b ). Notably, the fungi of the genus Metarhizium have been recognized for their ability to infect and eliminate a broad range of arthropods ( Zimmermann, 2007 ; Brunner-Mendoza et al, 2019 ; Vivekanandhan et al, 2022 ).…”