Effect of mixed infection with Trypanosoma cruzi and the fungus Metarhizium anisopliae on survival, parasitemia, and immune response in Triatoma pallidipennis (Hemiptera: Reduviidae).

Entomopathogenic fungi (EPF) are promising tools for controlling vectors of Chagas disease, yet the immunological effects of simultaneous infection with Trypanosoma cruzi and EPF remain largely unknown. We investigated how single infections with T. cruzi (Tc) or Metarhizium anisopliae (Ma), and coinfection (Tc+Ma), affect survival, parasitemia, and immune gene expression in Triatoma pallidipennis (Stål, 1872). Survival of T. pallidipennis differed significantly among treatments, insects only infected with Ma causing the greatest mortality. Parasitemia decreased notably in coinfected insects, suggesting interference between pathogens. Gene expression patterns varied across gut regions: phenoloxidase was strongly upregulated in Ma infections, but reduced in coinfection; defensins increased primarily in Tc infections; and lectins were elevated in Tc and Ma single infections but consistently suppressed in coinfection. These results indicate that M. anisopliae remains effective as a biocontrol agent even in infected insects with T. cruzi, and that competitive interactions between fungus and parasite modulate both parasitemia and the insect's immune response.