Hydrolysis of plant glycosides by cereal aphids

The activities of beta-fructofuranosidase, a-glucosidase and beta-glucosidase, in the saliva and whole body homogenates of the grain aphid, Sitobion avenae (Fabr.) and the bird cherry-oat aphid, Rhopalosiphum padi (L.) were detected. beta-Fructofuranosidase was the predominant enzyme among the glucosidases. The beta-glucosidase was effective in digesting both cellobiose and phenolic glucosides. There was a higher activity of beta-glucosidase in aphids reared on susceptible than on moderately resistant wheats. Both species of aphid readily digested sucrose and released glucose whereas starch digestion was attributed to the activity of microorganisms. Moreover, S. avenae showed lower activity of the beta-fructofuranosidase, alpha-and beta-glucosidase compared to R. padi. This may be related to differences in the composition of the food ingested by these aphids.