Biology of Phycodes radiata (Lepidoptera: Brachodidae) and its immune challenge to entomopathogenic fungi.

Abstract

Phycodes radiata is a significant pest of fig trees, causing extensive damage to fig orchards in the Semnan region of Iran in recent years. egg masses of P. radiata were collected from four Ficus carica cultivars, Zard Semnan, Ghermez Semnan, Zard Garmsar, and Ficus sp., and were subsequently reared under laboratory conditions. The study investigated the biological parameters of P. radiata when fed on four different fig cultivars. The feeding index parameters were significantly higher in the Zard Semnan cultivar than in the others. Hemocyte types observed in the larval hemolymph included prohemocytes, plasmatocytes, granulocytes, and oenocytoids, as identified via light microscopy. The pathogenicity of five isolates of entomopathogenic fungi: three isolates of Beauveria bassiana (B1, B2, and B3), one isolate of Metarhizium anisopliae, and one isolate of Lecanicillium muscarium were assessed against P. radiata larvae. The larvae were directly immersed in the fungal suspension for 6 seconds. Control larvae were treated similarly with Tween 80 (0.01%) and distilled water. Larval mortality was highest with the B2, B1, and B3 isolates, respectively. To evaluate hemocyte density in response to pathogenic fungi, fungal spores were injected into insect hemolymph, and hemocyte type changes were recorded at 1, 3, 6, 12, 24, 48, and 72 hours post-injection. The most pronounced effects were observed with the B1 and B2 isolates at 3 and 6 hours post-injection. Overall, the findings indicate that entomopathogenic fungi can effectively disrupt the growth and defense mechanisms of P. radiata, leading to impaired development and increased larval mortality.