Hellula undalis (Fabricius, 1781), a member of the Lepidoptera order belonging to the Pyralidae family, holds considerable status as a pest within warm geographical regions across the globe (Labou et al. 2017). Its origin traces back to Europe; however, it has incited substantial outbreaks in diverse Asian nations like India, Malaysia, and Vietnam (Kunjwal and Srivastava, 2018; Tran et al., 2018). The larvae of H. undalis exhibit an initial behaviour of tunnelling into the stems of nascent shoots. These larvae undergo a transition as they get older and begin to constipate the leaves and leaf stems. In the process, they construct a silk enclosure around their feeding vicinity, within which accumulates their excrement. The larvae of H. undalis initially bore into the stems of growing shoots, while mature larvae mine the leaves and leaf stems. They create a silk web around their feeding area, which becomes filled with their waste material. During the pre-heading stage, a single larva's feeding damage to a cabbage plant can result in multiple non-marketable heads or even plant death. Remarkably, even the feeding activity of a solitary larva on a cabbage plant during its pre-heading phase can culminate in the demise of the plant or yield multiple heads that lack market value (Sivapragasan, 2005).

Significant disadvantages resulting from overuse of pesticides include harm to native predators and ecosystem degradation (Khan et al., 2012; Khan et al., 2023). In the context of ecological well-being, the adoption of biocontrol agents for the sustainable oversight of insect pests experiencing rapid growth. Fungal bioagents that initiate infections within insects present a potent avenue for ecologically considerate management of insect pests. Biocontrol agents that possess noteworthy virulence traits, such as entomopathogenic fungi, are swiftly emerging as credible substitutes for synthetic pesticides (Islam et al., 2021). Global demand for the formulation of microbial bio-pesticides as integral components of integrated pest management initiatives and the increasing necessity for pesticides devoid of chemical constituents are on the rise, as reported by Zaki et al. (2020).

The entomopathogenic fungus satisfies the prerequisites for a potential natural factor inducing insect mortality (Boomsma et al., 2014). Established models for investigating the biological regulation of pest populations through fungal entomopathogens encompass Beauveria bassiana (Bals.-Criv.) Vuill and Metarhizium anisopliae (Metchnikoff) Sorokin, both widely recognized for their pathogenic effects on numerous insect species. These mycobiocontrol agents have gained global utilization in the agricultural sector for the biocontrol of insects (Sandhu et al., 2012; Shehzad et al., 2021; Shanker et al., 2023).

The present investigation was carried out to evaluate the effectiveness of a local isolate of M. anisopliae against the fourth instar larvae of H. undalis. These larvae were reared using a natural dietary regimen within controlled laboratory settings.

Entomopathogenic fungi play a crucial role in regulating insect populations. In particular, M. anisopliae is important as a natural control agent and source of mycoinsecticides for the control of numerous lepidopteran pests worldwide (Asi et al., 2013). Previous studies have extensively investigated the potential of M. anisopliae as a biological control agent (Lin et al., 2007). The effectiveness of M. anisopliae as an entomopathogenic fungus has been demonstrated against a variety of insects, including Lepidoptera, Coleoptera, Hemiptera and others (Shehzad et al., 2021; Kumar et al., 2023; Shanker et al ., 2023).

The aim of the present study was to evaluate the effectiveness of a locally identified isolate of the entomopathogenic fungus M. anisopliae against H. undalis larvae under controlled laboratory conditions. The results of this investigation provide insight into the potential of this fungus as a biocontrol agent for the control of H. undalis populations.

The efficacy of a M. anisopliae isolate against fourth instar larvae of H. undalis was investigated in this study. The experiment involved exposing the larvae to varying concentrations of M. anisopliae spores and monitoring mortality percentages at different time intervals. The results revealed direct relationship to the concentration of treatment with increasing spore concentrations leading to higher mortality rates. At the lowest concentration tested (1 × 10³ spores ml^-1), no mortality was observed within the initial 24 h, but over time, mortality rates increased to 41.66% after 120 h. As the spore concentration increased to 1 × 10¹⁰ spores ml^-1, mortality percentages steadily increase to 86.88% after 120 h of exposure (p ≤ 0.05) (Table 1). These findings suggest that the effectiveness of M. anisopliae against H. undalis larvae is concentration-dependent.

The LT₅₀ decreased as concentrations of the spore increased. The LT₅₀ ranged from 7.91 days for the lowest spore concentration (1 × 10³ spores ml^-1) to 5.43 days for the highest spore concentration (1 × 10¹⁰ spores ml^-1). Similarly, the LT₉₀ exhibited a decreasing trend with higher spore concentrations. The LT₉₀ values ranged from 12.25 days for the lowest spore concentration (1 × 10³ spores ml^-1) to 9.29 days for the highest concentration (1 × 10¹⁰ spores ml^-1) (p ≤ 0.05) (Table 1). These findings highlight the potential of M. anisopliae as a biological control agent against H. undalis larvae under laboratory conditions.

Previously, similar studies were conducted involving different insects. For instance, Nguyen et al., (2007) reported an 87.00% mortality rate in 4th instar larvae of H. armigera after a two-week exposure period. Additionally, Fite et al. (2020) observed a 71.00% mortality rate at a concentration of 1 × 10⁹ spores ml⁻¹ after eleven days of post-treatment. Similarly, Rijal et al. (2008) and Sabry et al. (2011) documented mortality rates of 65.33%, 86.67%, 60.00%, and 80.00% for second and third instar larvae with a conidial concentration of 1 × 10⁷ spores ml⁻¹ after six, seven-, and ten-days post-treatment, respectively. Shanker et al. (2023) and Yanar et al. (2023) asserted that the highest concentration exhibits greater efficacy against the insect. The LT₅₀ values varied with conidial concentrations, with Tahir et al. (2019) and Fite et al. (2020) reporting 6.20 days and 3.71 days at 1 × 10⁹ spores ml⁻¹, respectively. Moreover, Nahar et al. (2008) and Nguyen et al. (2007) found LT₅₀ values of 3.4 days and 3.00 days for a conidial concentration of 1.0 × 10⁷ ml⁻¹, respectively. This study represents the first experimental finding aimed at evaluating the efficacy of M. anisopliae against the larvae of H. undalis under laboratory conditions. Due to the absence of comparable findings, the current results are contextualized by drawing parallels with other members of the same family, Pyralidae. The virulence of different concentrations of M. anisopliae on H. undalis larvae exhibited similarities to outcomes reported by Ramanujam et al. (2015). Specifically, a concentration of 10⁷ conidia/ml resulted in a mortality rate of 90% in Chilo partellus, a member of the same family, after 10 days of inoculation.

The results showed that the application of M. anisopliae spore suspension resulted in a significant increase in larval mortality compared to the control group. This result is consistent with previous research that has suggested insecticidal properties of Metarhizium species against various insect pests. The mortality rate observed in the treatment group supports the potential of this locally identified isolate as a biopesticide to control H. undalis infestations.