Entomoparasitic nematodes Sychnotylenchus sp. (Anguinidae) on the four-eyed fir bark beetle Polygraphus proximus: effects on the host's immunity and its susceptibility to Beauveria bassiana

Abstract

This study for the first time demonstrated evidence of immunosuppressive influence of the entomoparasitic nematode Sychnotylenchus sp. (Anguinidae) on the four-eyed fir bark beetle Polygraphus proximus. We detected significant decrease of phenoloxidase activity and non-specific esterases and an increase of glutathione-S-transferase rates in nematode-infected beetles. Although infection by the nematode did not cause significant increase of mortality of the four-eyed fir bark beetle, it did enhance its susceptibility to infection by Beauveria bassiana. Our observations indicated synergetic effect between nematode and fungus infections. Thus, it was shown that the nematode suppresses immunity of its host only to the extent required for effective implementation of phoresy within the bark beetle.