Monochamus alternatus Hope (Coleoptera: Cerambycidae) is the main borer of several pine species (e.g. Pinus massoniana Lamb) and is also the primary vector of the pest pine wood nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle (Aphelenchida: Parasitaphelenchidae). Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) is a natural enemy and an ectoparasitoid of M. alternatus. We studied the effects of parasitism by D. helophoroides on the hemolymph saccharide content in parasitized M. alternatus larvae. Our results showed that hemolymph saccharide content was altered by parasitism. For example, in comparison to unparasitized insects, the total sugar content increased in larvae 12 h after parasitism, the reducing sugar content declined at 24 h after parasitism but increased at 72 h after parasitism, and the trehalose content was inhibited at 6 h and 24 h after parasitism. These results indicate that D. helophoroides larvae may regulate saccharide metabolism in M. alternatus larvae, resulting in the changes of saccharide content in host hemolymph.