Abstract

This study investigates the glutathione-immunity interaction upon infection of both larval and adult stages of Aedes caspius with Bacillus thuringiensis kurstaki (Btk). The anti-oxidative stress, in terms of glutathione (GSH) titer, and melanization immune response, in terms of phenoloxidase (PO) titer, was investigated. Data from Btk-infected larvae showed no or significant lower GSH titer at 12 or 24 h post-treatment respectively compared to control larvae. On the other hand, no PO activity was detected at both time points post-Btk infection. This may indicate that oxidative stress in larvae was increased while antibacterial response was blocked upon Btk infection. Bacteria-inoculated adult mosquitoes showed higher GSH activity at 12 and 24 h post-inoculation with Btk and E. coli compared to control ones, and was more pronounced in E. coli-inoculated mosquitoes. On the other hand, PO titer showed significant higher PO activity at 12 and 24 h post-inoculation with each kind of bacteria, but was more pronounced against E. coli.These results may indicate that antibacterial and antioxidtive responses are more pronounced against Btk in adult stage compared to larval stage, which may be attributed to the difference in the mode of infection and/or mosquito stage. Moreover, inhibition of both antibacterial and antioxidtive responses upon Btk infection in larval stage may explain its high larvicidal activity. More markers of oxidative stress in Btk-infected mosquitoes still to be investigated.

Key words: Immune response, antioxidant response, oxidative stress, glutathione, Aedes caspius, Bacillus thuringiensis.