Immune suppression and metabolic reprogramming in Bactrocera dorsalis parasitized by Fopius arisanus

Bactrocera dorsalis is a major horticultural pest. Biocontrol using parasitoids, such as Fopius arisanus, is a sustainable tool for managing this pest. However, the mechanisms enabling the successful parasitism of B. dorsalis are poorly understood. Using transcriptomic profiling, cellular bioassays, and targeted metabolite analyses, we investigated how F. arisanus modulates the immunity and metabolic activity of B. dorsalis to achieve a high parasitism rate. Our results revealed a weak and late encapsulation response of B. dorsalis towards F. arisanus. Additionally, parasitism reduced the number of circulating haemocytes by 35%, lowered constitutive granulocyte counts and inhibited phenoloxidase activity in B. dorsalis, suggesting active suppression of the host immune responses. Genes linked to cytoskeletal dynamics, stress response, and transcription were downregulated, also indicating that F. arisanus actively suppresses B. dorsalis immunity. Furthermore, parasitism reduced systemic triglyceride content but increased haemolymph triglyceride levels by 65% in B. dorsalis larvae, indicating that this parasitoid reprogrammes the metabolic profile of its host for its own development. This was supported by the differential upregulation of genes involved in glycolysis, amino acid metabolism and fatty acid biosynthesis. Overall, our findings suggest that immune suppression and metabolic reprogramming play a role in the successful parasitism of B. dorsalis by F. arisanus.