Objective To clarify the classification of two entomopathogenic fungi isolated from the pupae of Milionia basalis and their biocontrol potential against Lymantria xylina, providing a theoretical basis for the biological control of the major pests affecting the coastal shelter forest tree species Casuarina equisetifolia.

Methods This study determined the taxonomic status of two Cordyceps fungi through morphological characteristics and rDNA-ITS, LSU, and TEF sequence analysis. Their pathogenicity to L.xylina larvae was assessed using bioassays, followed by the optimization of liquid fermentation conditions for both fungal strains.

Results Based on the morphological features, cultural characteristics, and phylogenetic analysis results, both fungal strains were identified as Cordyceps cateniannulata. After inoculating nun moth larvae with a spore suspension of 1.0 × 10⁸ spores/mL from strains CcQZ-02 and CcQZ-03 for 15 days, the cumulative corrected mortality rates were 77.17 ± 1.41% and 63.30 ± 12.71%, respectively, with LT₅₀ values of 6.88 days and 8.34 days. The growth of strains CcQZ-02 and CcQZ-03 on different liquid culture media showed that the mycelial dry weight was the highest in Czapek's solution, which was 13.71 mg·mL⁻¹ and 10.76 mg·mL⁻¹ respectively. The second-best media was Sabouraud dextrose broth, followed by synthetic low-nutrition medium. Among the tested carbon and nitrogen sources, starch and beef extract were the most effective for both strains.

Conclusion Both C. cateniannulata strains exhibited significant pathogenicity against L.xylina larvae. Czapek medium, with starch as the carbon source and beef extract as the nitrogen source is conducive to the growth of both strains' mycelia, indicating their potential as effective biocontrol agents for further development.