02631nas a2200253   4500008004100000245013600041210006900177300001300246490000700259520178500266653003002051653003002081653001502111653001602126653001702142653002102159653002602180653001902206653001802225653002202243100001602265700001902281856007702300       2008                        eng d00aHost-plant quality alters grass/forb consumption by a mixed-feeding insect herbivore, Melanoplus bivittauts (Orthoptera: Acrididae)0 aHostplant quality alters grassforb consumption by a mixedfeeding  a546 -5540 v333 a<p>1.&ensp;Factors affecting the nutritional ecology of mixed-feeding, polyphagous herbivores are poorly understood. Mixed-feeding herbivores do better when they consume both forb and grass species although they typically feed primarily on forbs, which are of relatively higher protein content than grasses. 2.&ensp;In a field experiment, we examined the effects of nitrogen and phosphorus fertilization and associated changes in host-plant C:N:P on proportional grass consumption by a mixed-feeding insect herbivore, Melanoplus bivittatus, using natural abundance stable carbon isotope (12C/13C) methods. We also examined a grass-feeding (Phoetaliotes nebrascensis) and forb-feeding (Hesperotettix viridis) species. 3.&ensp;The C isotope signatures of M. bivittatus collected from plots fertilized with nitrogen (+N), phosphorus (+P), nitrogen and phosphorus (+N+P) and no fertilizer were compared with the C isotope signatures of plants in those plots to determine the proportion of assimilated C derived from C4 grasses and C3 forbs in each plot. We also examined the relationship between M. bivittatus diets and plant C:N:P stoichiometry. 4.&ensp;The proportion of grass assimilated approximately doubled in N-fertilized treatments (39.1 &plusmn; 0.1%) compared with non-fertilized treatments (19 &plusmn; &lt;0.1%), an increase associated with decreased C:N and increased N:P of grasses. 5.&ensp;These results indicate that mixed-feeding M. bivittatus can selectively feed to balance C:N:P intake even when choosing between two structurally and chemically different groups of plants. 6.&ensp;The strong relationship between diet selection and grass stoichiometry also suggests that plant nutrient composition may be more important than defensive chemistry in food choice.</p>10aC3 photosynthetic pathway10aC4 photosynthetic pathway10aCarbon (C)10agrasshopper10anitrogen (N)10aoptimal foraging10aOrthoptera: Acrididae10aphosphorus (P)10astoichiometry10atallgrass prairie1 aJonas, J.L.1 aJoern, Anthony  uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2311.2008.01004.x