Histological and nucleic acids alterations in Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) induced by Streptomyces lavendulae (Streptomycetaceae) culture filtrate

Histological and nucleic-acid alterations induced by Streptomyces lavendulae (Streptomycetaceae) culture filtrate on the 2nd instar larvae of Spodoptera littoralis (Boisd.) were studied. Using thin-film techniques, larvae were exposed to a concentration of 226 CFU cm-2 for 48 h, which caused 84% larval mortality. The filtrate induced deleterious histological changes, with clear signs of apoptosis in the mid-gut and brain tissues. Using gel electrophoresis, the intensity of RNA decreased while fragmented DNA increased relative to controls. These DNA fragments are from apoptosis, as supported by histopathological observations. Histochemically, total protein content decreased in mid-gut cells, consistent with the electrophoretic pattern of the RNA. These effects clearly indicated that S.lavendulae releases a toxin containing bioactive compound(s) whose mode of action could be on the nervous system and /or insect immune system.