Comparative response of Spodoptera litura challenged per os with Serratia marcescens strains differing in virulence

•Protease activity was much higher in gut of non-virulent S. marcescens treated larvae.•Antioxidant enzyme activity was higher in gut of virulent S. marcescens treated larvae.•Higher defense response was observed in hemolymph of virulent S. marcescens challenged larvae.•More proteins were over-expressed in gut of non-virulent S. marcescens treated larvae.•Most of the identified differentially expressed proteins, were involved in insect innate immune response.