Distribution, abundance, and short-term persistence of grape phylloxera (Homoptera : Phylloxeridae) populations in two regions of the native range

Studies of genetic structure in natural populations of herbivores are stren gthened when detailed data are available on distribution and relative popul ation size across space and host plants. No studies have documented in dept h how grape phylloxera, Daktulosphaira vitifoliae Fitch, a major pest of cu ltivated grapes, is distributed among its host plants or among sites within regions of its native range. We surveyed the frequency of foliar grape phy lloxera, and collected data that described the relative population sizes of grape phylloxera among host plant species, sites, and dates within 2, regi ons of the native range (Missouri/Arkansas and the southwest United States) . Three of 5 grape species surveyed in Missouri/Arkansas had populations of phylloxera. We found that host species in this region were ranked in one y ear, but not another. We found weak evidence that populations on different host species are regulated independently. Most, but not all, sites with gra pe habitat in the fragmented topography of the southwest had populations of phylloxera Their sizes varied widely among sites, but not across dates. We found an extinction rate of 0.23/yr of colonies on vines in the southwest United States The implications of the data for the genetic structure of gra pe phylloxera populations are discussed.