Immuno-physiological adaptations confer wax moth Galleria mellonella resistance to Bacillus thuringiensis

The Greater wax moth, Galleria mellonella, is a pest of beehives and is gaining a reputation as an important organism for modelling host-pathogen interactions. A G. mellonella population was selected for enhanced resistance to Bacillus thuringiensis (Bt), which is a widely-used entomopathogenic biological pesticide. Resistance and defence mechanisms were investigated in this insect line, and compared with a non-selected (suspectible) line. We also investigated the possible cost of those survival strategies. In the uninfected state, resistant insects exhibited enhanced basal expression of genes related to regeneration and amelioration of Bt toxin activity in the midgut. In addition, these insects also exhibited elevated activity of genes linked to inflammation/stress management, and fat body immune defences. Following oral infection with Bt, several of these genes wwere more highly expressed in resistant insect than in the susceptible line. Gene expression analysis reveals a pattern of resistance mechanisms targeted to anatomical sites predominantly attacked by Bt. The resistant insect concentrates its response towards tissue repair. Unlike the susceptible insects, Bt infection significantly reduced the diversity and richness (abundance) of the gut microbiota in the resistant insects. These observations suggest that the resistant line not only has a more intact midgut but is secreting antimicrobial factors into the gut lumen which not only mitigate Bt activity but also affect the viability of other gut bacteria. Remarkably the resistant line employs these multifactorial adaptations for resistance to Bt without any detectable negative trade-off, since the insects also exhibited higher fecundity