BEHAVIORAL AND REPRODUCTIVE RESPONSE OF CAGED EMPOASCA-FABAE (HOMOPTERA, CICADELLIDAE) TO VEGETATION DENSITY OF A HOST LEGUME AND A NONHOSTGRASS

Behavior and reproduction of potato leafhopper, Empoasca fabae (Harris ) (Homoptera: Cicadellidae), were examined in the laboratory in respon se to varying densities of leafhoppers, a host legume (alfalfa, Medica go sativa L.), and a non-host grass (large crabgrass, Digitaria sangui nalis L.). A series of caged treatments with increasing crabgrass dens ity per cage resulted in a corresponding series of decreasing oviposit ion and decreasing number of primary oocytes per female. Oviposition a nd number of primary oocytes were reduced by approximately 30% at the highest grass density. However, adult activity as measured by percenta ge of leafhoppers on alfalfa, in flights per minute, and on sides of c age, remained unchanged with increasing crabgrass density. When respon ses given at crabgrass densities were compared with pure alfalfa of eq uivalent vegetation density (plant surface area), activity in the pres ence of crabgrass was two to four times larger than alfalfa alone of e quivalent vegetation density, with the highest increases occurring aft er 1700 h and with greatest crabgrass density. Results suggest that gr eater relative activity induced by crabgrass volatiles may have been r esponsible for reduced oviposition and reduced tenure time on alfalfa nearest to crabgrass in two-choice tests.