Contributions of cellular and humoral immunity of Galleria mellonella larvae in defence against oral infection by Bacillus thuringiensis

[Display omitted] •Immune reactions of wax moth G. mellonella uncovered during peroral Bt infection.•Low dose of Bt resulted in significantly elevated both cellular and humoral immunity.•High dose of Bt triggered elevated haemolymph PO and lysozyme-like activity.•High dose decreased the coagulation index and activity of PO in haemocytes.•During Bt infection, the pool of circulating haemocytes became depleted. In this study the cellular and humoral immune reactions of the Greater wax moth Galleria mellonella have been investigated during bacterial infection caused by oral administration of Bacillus thuringiensis. Two different dose strengths were investigated to assess the contribution of immune parameters to induced Bt resistance. Low-dose (sublethal LC15) infection resulted in significantly elevated haemolymph phenoloxidase and lysozyme-like activity, enhanced phagocytic activity of haemocytes, and increased encapsulation responses in infected larvae at 48 and 72h post infection. Higher doses of Bt (half-lethal LC50) also triggered significantly elevated haemolymph phenoloxidase and lysozyme-like activity, but decreased the coagulation index and activity of phenoloxidase in haemocytes of infected larvae. In both types of infection, the pool of circulating haemocytes became depleted. The importance of cellular and humoral immune reactions in induced insect resistance to intestinal bacterial infection Bt is herein discussed.