| The apparent repellency of grass was investigated in order to determine the means by which potato leafhoppers perceive the presence of grass, to determine the behavioral changes caused by grass which lower abundance in alfalfa, and to test the resource concentration hypothesis for the potato leafhopper in alfalfa.;In an alfalfa field at dusk, a higher percentage of the leafhoppers in grassy alfalfa were in flight and had fewer oocytes/female than in grass-free alfalfa, supporting conclusions from laboratory studies that presence of grass increases flight and decreases the number of oocytes/female.;Though potato leafhoppers are highly polyphagous, they are facultatively monophagous in an alfalfa field, therefore it is an ideal candidate for testing the resource concentration hypothesis. Two aspects of the resource concentration hypothesis were tested in field sampling: plant density (thinned and unthinned alfalfa) and plant diversity (weedy and weed-free). Results showed that leafhoppers were more abundant on sparse alfalfa (leafhoppers/kg or leafhoppers/stem), while absolute density was higher on dense alfalfa (leafhoppers/m;In adult location and oviposition choice tests leafhoppers used primarily olfaction to perceive grass. In no-choice tests potato leafhoppers responded with greater movement rates, and both oocyte development and oviposition rates were decreased in the presence of grass in a dose-dependent manner. In addition, feeding of tethered leafhoppers on alfalfa was decreased in the presence of grass. Grass volatiles acted as locomotory stimulants, interrupting oviposition and feeding, and in addition having possible repellant effects. |
