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

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

The Greater wax moth Galleria mellonella was used as a model organism to elucidate the underlying mechanisms of host-pathogen interactions following challenge by the bacterial bio-pesticide Bacillus thuringiensis. This bacterium is a vital tool in integrated pest management and it is thought that it elicits insect killing via a combination of toxin production, dysbiosis and / or septicaemia. However, the nature of the immune & stress responses triggered in host insects has not yet been fully evaluated, nor has the nature of possible resistance or tolerance mechanisms. This paper addresses these issues, and proposes possible tolerance mechanisms that will help inform future biocontrol strategies