EFFECTS OF HOST-PLANT NITROGEN ON THE PREFERENCE AND PERFORMANCE OF LABORATORY POPULATIONS OF CARNEOCEPHALA-FLORIDANA (HOMOPTERA, CICADELLIDAE)

Carneocephala floridana Ball is an oligophagous leafhopper that switches host plants seasonally and feeds primarily on the salt-marsh cord grass, Spartina alterniflora Loiseleur-Deslongchamps, during the winter. In the laboratory, we examined how variation in foliar nitrogen of S. alterniflora influenced the choice of cord-grass culms by C. floridana as feeding and oviposition sites. We also examined the effects of host-plant nitrogen on leafhopper oviposition rate, body size, and fecundity. Given a choice among cord-grass culms grown under four fertilization regimes, groups of adult female leafhoppers preferentially fed on culms that were higher in foliar nitrogen. Although the total number of eggs laid was highest on plants of superior quality (as measured by nitrogen content), the rate of oviposition did not differ among plants of different nitrogen levels. Leafhoppers reared from first instar to adult on highly fertilized plants were significantly larger (had higher dry body weight) than those reared on unfertilized or minimally fertilized plants. A significant relationship between body weight and maternal sibship was also found for males, but not for females. Larger body size is advantageous because larger adult females have higher daily oviposition rates than smaller ones. We suggest that C. floridana that choose plants with higher nitrogen content under natural conditions enjoy a selective advantage and that choice within a host-plant species (and perhaps among species) is correlated with host-plant nitrogen content.