FEEDING-BEHAVIOR OF GRAMINIVOROUS GRASSHOPPERS IN RESPONSE TO HOST-PLANT EXTRACTS, ALKALOIDS, AND TANNINS

Secondary metabolites exhibit the potential to direct food selection b y grass-feeding (graminivorous) grasshoppers. We examined the effects of plant extracts and representative secondary metabolites on the feed ing behavior of two such grasshoppers, Ageneotettix deorum (Scudder) a nd Phoetaliotes nebrascensis (Scudder). Three alkaloids and two tannin s were bioassayed for their activity as feeding deterrent allelochemic als, as were extracts from the foliage of the graminoids commonly eate n by these grasshoppers: Agropyron smithii Rydb., Andropogon hallii Ha ck., Andropogon scoparius Michx., Bouteloua gracilis (H. B. K) Lag. ex Griffiths, Carex heliophila Mack. and Stipa comata Trin. and Rupr. Al kaloids strongly deterred feeding but tannins only exhibited a weak ef fect, even when present at four times the concentration of total pheno lics typical for these graminoids. Host-plant extracts also exhibited weak effects, such that we found no evidence for either strong deterre nce or phagostimulation. Our results for alkaloids and host-plant extr acts are consistent with the view that grass-feeding grasshoppers may be restricted to graminoids because of: (1) the presence of deterrents in nonhosts and (2) the absence of deterrents in hosts. However, our data for tannins show that these are unlikely to be effective barriers to herbivory by these grasshoppers.