Non-Cellular Response of Flour Moth, Ephestia kuehniella Challenged with Bacillus thuringiensis and Beauveria bassiana

The innate immune system of insects comprises both cellular and humoral mechanisms. The phenoloxidase activity and the production of antimicrobial peptides/ proteins (AMPs) are the most important parts of insect immune system. In this study, we investigated the humoral response of flour moth, Ephestia kuehniella challenged with two different entomopathogens, Bacillus thuringiensis (Bt) and Beauveria bassiana. The suspension of Bt and/or B. bassiana was injected to the fifth instar larvae of E. kuehniella. Afterwards, the phenoloxidase activity and the possible induction of AMPs in the haemolymph of treated larvae was assessed. Moreover, the antimicrobial activity of the collected haemolymph was examined against a Bt strain. As a result, the phenoloxidase activity of treated larvae was significantly reduced in comparison to non-treated larvae. Also, no band has been detected corresponding to insect AMPs in the haemolymph of immune-challenged larvae with both bacterial and fungal pathogens. Furthermore, the haemolymph did not show any antimicrobial activity in vitro against the tested Bt strain. Based on our findings, it can be concluded that the non-cellular immune system of flour moth did not respond to the cell walls of applied entomopathogens, thus further investigations are needed to determine the possible application of E. kuehniella as a model in the insect immune system studies against these two entomopathogens.