Histopathological studies on Spodoptera litura against entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae
M Raja, V Vinolia
The family Cruciferae contains species of great economic importance, providing much of the world's winter vegetables. These include cabbage, broccoli, cauliflower, Brussels sprouts, turnip, radish, rapeseed and mustard. Among the vegetable brassicas in India, cabbage is grown on a large scale accounting to 10% of the world production. Microbial control agents like bacteria (Bacillus thuringiensis), viruses (Nuclear Polyhedrosis Virus) and entomopathogenic fungi (such as Beauveria, Metarhizium etc.) are potential against lepidopteran larvae. The entomopathogenic fungal formulations are eco-friendly, economic, target-specific and easily biodegradable.Spodoptera litura was studied histologically in comparison to untreated larvae for the growth and development of Beauveria bassiana and Metarhizium anisopliae. Germ tube penetration through the insect cuticle was first observed by 2.5 days after inoculation. The germ tubes grew along the endocuticle between the epidermis and the exocuticle laminae and produced lateral branches. Lysis of the endocuticle occurred before hyphae invaded the epidermis. The hyphae penetrated the epidermis and reached the hemocoel within two and a half days after inoculation. After reaching the hemocoel, the invasive hyphae transformed into hyphal bodies that replicated in the hemolymph by budding. Noninvasive hyphal bodies filled the hemocoel in a few days and all tissues became colonized. Nevertheless, these processes did not affect larval feeding activity or digestion and they appeared to be grossly healthy. The noninvasive hyphal bodies converted to invasive mycelia at 5.5 to 6 days after inoculation, completely ramified throughout all larval tissues, penetrated the cuticle and emerged through it. However, the emerging hyphae differed from the hyphae found in the early stages of infection in that they grew perpendicular to the cuticular surface rather than parallel to it. The hyphae emerged from the cuticle of the dead larva and grew allover the surface forming a white myceliam and later formed green mat. Subsequently, cadavers became completely covered by green conidia. The complete developmental cycle of this M. anisopliae isolate in S. litura lasted approximately 8 to 9 days.
M Raja, V Vinolia. Histopathological studies on Spodoptera litura against entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae. International Journal of Entomology Research, Volume 6, Issue 2, 2021, Pages 268-272