Morphological and multilocus identification of a Philippine indigenous Cordyceps javanica (Hypocreales: Cordycipitaceae) and its biocontrol potential against the kanzawa spider mite Tetranychus kanzawai Kishida (1927) (Acari: Tetranychidae)

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Abstract

Cordyceps javanica (Frieder. & Bally) Kepler et al. (2017) (Hypocreales: Cordycipitaceae) is an entomopathogenic fungus (EPF) which infects diverse arthropod hosts. This study assessed the pathogenicity and virulence of a newly identified Philippine indigenous isolate, C. javanica NIJVFBL2024 using morphological and combined ITS, Tef-1α, and LSU molecular markers, against the spider mite Tetranychus kanzawai Kishida (1927), a major pest affecting crop productivity. Given rising resistance and ecological concerns linked to chemical pesticides, EPFs offer promising alternatives. Pathogenicity was first tested on ten (10) Tenebrio molitor larvae using a dipping bioassay across three conidial concentrations (3.24 × 10⁸, 2.28 × 10⁷, 6.08 × 10⁶). Larvae were monitored for mycosis at 1, 3, and 7 days post-treatment. For T. kanzawai, twenty (20) 3 days-old female adults were subjected to a modified leaf-disc bioassay with spray application using three fungal concentrations (1 × 10⁶, 1 × 10⁷, 1 × 10⁸ conidia/mL), spirodiclofen (0.02 % v/v), and a negative control. Evaluations of mycosis rates were performed at 18–99 h post-inoculation. All treatments were replicated four times and experiments were independently repeated twice. C. javanica NIJVFBL2024 exhibited strong virulence against both hosts. T. molitor showed 95 % mycosis at the highest concentration by day 3, and >85 % across all treatments by day 7. In T. kanzawai, fungal colonization induced progressive mycosis, with the highest conidial concentration (92.5 ± 6.45 %) outperforming spirodiclofen mortality (32.28 ± 16.76 %) by 53 h. By 99 h, the highest concentration exhibited a final mycosis rate of 98.75 ± 2.5 %. Probit analysis revealed that the median lethal concentration (LC₅₀) decreased from 8.69 × 10⁶ conidia/mL at 35 h to 6.72 × 10⁵ conidia/mL at 71 h. Conversely, the median lethal time (LT₅₀) decreased as concentration increased, from 54.51 h at 1 × 10⁶ conidia/mL to just 26.59 h at 1 × 10⁸ conidia/mL. The highest concentration was highly virulent, achieving an LT₅₀ of 26.59 h, which was more rapid than the chemical acaricide spirodiclofen (LT₅₀ = 66.18 h). This is the first report of an indigenous C. javanica isolate from the Philippines with demonstrated biocontrol efficacy against T. kanzawai. Field validation is recommended to support its integration into pest management programs.