Differential cellular encapsulation in six termite species against the infection of Metarhizium anisopliae

Six termite species (Termopsidae: Hodotermopsis sjoestedti, Hodotermitidae: Hodotermes mossambicus, Rhinotermitidae: Reticulitermes flavipes and Prorhinotermes canalifrons, Kalotermitidae: Kalotermes flavicollis, and Termitidae: Nasutitermes voeltzkowi) were exposed to conidia of the entomopathogenic fungus Metarhizium anisopliae. All species showed various susceptibility to the fungus. Histopathological analysis showed that all termite species produce an immune reaction to prevent fungal penetration through the cuticle. The hemocytes aggregation around the point of infection was quantified for each species and it was shown that the cellular encapsulation expression and intensity differed among species, which may explain the difference in susceptibility. Our results suggest that termite species that live in a habitat with a potentially high microbial diversity, evolved a specific immune response to some soil entomopathogens. This response can be efficient and cost effective in these species (H. sjoestedti, R. flavipes). However, species that live in a habitat with a low microbial load showed an inefficient cellular encapsulation with a high physiological cost (K. flavicollis). Therefore, cellular encapsulation, as part of the insect immune response, differed greatly among the tested species, and we suggest that this immunity is partially adapted to the habitat of each species.