Susceptibility of Pre-adult Biological Stages of Mythimna separata (Walker) (Lepidoptera: Noctuidae) to Three Entomopathogenic Fungi (Hypocreales)

Authors

Melissa P. Montecalvo, University of the Philippines Los BanosFollow
Marcela M. Navasero, University of the Philippines Los Baños

Publication Date

3-1-2023

Abstract

Armyworms are polyphagous insect pests of agricultural crops. Their population is usually managed below threshold level using insecticides. However, a single control measure is insufficient to attain a sustainable pest management. Hence, this research was conducted to assess the three species of entomopathogenic fungi as potential biological control agents against Mythimna separata (Walker) or paddy armyworm. Dose mortality assays were conducted to determine the pathogenicity of Beauveria bassiana (Bals.) Vuill., Metarhizium anisopliae (Metschn.) Sorokin, and Metarhizium rileyi (Farlow) Kepler, S.A. Rehner and Humber against various biological stages of M. separata including egg, 1^st to 6^th larval instars, prepupa, and pupa. These entomopathogenic fungi did not have ovicidal activity but affected the survivorship of the resulting neonates. Exposure of eggs to B. bassiana, M. anisopliae, and M. rileyi infected 64, 60, and 70 % of the resulting neonates, respectively. Adult emergence was also reduced in fungal-treated (29% in B. bassiana, 10% in M. anisopliae, and 10% in M. rileyi) as compared with 64% in control. At 7 d after treatment, M. rileyi applied at 1 x 10⁵ to 1 x 10⁹ conidia/mL was the most pathogenic causing a mean larval mortality of up to 70% as compared to B. bassiana and M. anisopliae with less than 10% mortality. Among the larval instars, the 1^st, 2^nd, and 3^rd were the most susceptible to fungal infection. Conidial concentrations (1 x 10⁸ and 1 x 10⁹ conidia/mL) induced the highest larval mortalities as compared to the lower conidial concentrations (1 x 10⁵ and 1 x 10⁷ conidia/mL) of the entomopathogenic fungi. The prepupal and pupal stages were also slightly susceptible to the entomopathogenic fungi. These findings showed the pathogenic effect of the entomopathogenic fungi particularly M. rileyi to M. separata.

Recommended Citation

Montecalvo, Melissa P. and Navasero, Marcela M. (2023) "Susceptibility of Pre-adult Biological Stages of Mythimna separata (Walker) (Lepidoptera: Noctuidae) to Three Entomopathogenic Fungi (Hypocreales)," The Philippine Agricultural Scientist: Vol. 106: No. 1, Article 2.
Available at: https://www.ukdr.uplb.edu.ph/pas/vol106/iss1/2