Immune response of Chilo suppressalis Walker (Lepidoptera: Crambidae) larvae to different entomopathogenic fungi

The current study reports mortality and effects on cellular immune response of several entomopathogenic fungi including isoleates BB1, BB2 and BB3 of Beauveria bassiana, Metarhizium anisopliae, Isaria fumosoroseus and Lecanicilium lecanii against larvae of Chilo suppressalis. Prohemocytes, granulocytes, plasmatocytes and oenocytoids were identified as the main circulating hemocytes in the hemolymph of larvae using Giemsa staining solution. Entomopathogenic fungi caused differential mortality on larvae: BB1, BB3, M. anisopliae lead to the highest mortality on larvae and L. lecanii caused the lowest mortality. The highest numbers of total hemocytes were observed 3 h post-injection of B. bassiana isolates and 6 h for the other treatments. The highest numbers of plasmatocytes were observed 3 h post-injection of BB1 and Tween 80, whereas BB2, BB3, M. anisopliae, I. fumosoroseus and L. lecani caused plasmatocyte increase 6 h post-injection. Similar results were obtained in case of granulocytes but only Tween 80 showed the highest number of hemocytes 3 h post-injection. The highest numbers of nodules were found at various time intervals after injection of fungal isolates and latex bead. The highest activities of phenoloxidase were observed 12 h post-injection by BbB1, BbB3, M. anisopliae and latex bead; 3-6 h post-injection by BbB2, 6 h post-injection by I. fumosoroseus and 3-6 h post-injection by L. lecanii. Our data demonstrate the possibility of utilizing different fungal extracts in the field to help reduce the risk of resistance evolution in C. suppressalis and encourage experimentations aimed to increase the number of biological control agent for insect pests such as the striped rice stem borer C. suppressalis.