Colonization of ecological islands: Galling aphid populations (Sternorrhyncha: Aphidoidea: Pemphigidae) on recovering Pistacia trees after destruction by fire

Pistacia palaestina (Anacardiaceae) is a common tree in the natural forest of Mt. Carmel, Israel, and the primary host of five common species of gall-forming aphids (Sternorrhyncha: Aphidoidea: Pemphigidae: Fordinae). After a forest fire, resprouting P. palaestina trees, which are colonized by migrants from outside the burned area, become "ecological islands" for host-specific herbivores. A portion of the Carmel National Park was destroyed by fire in September of 1989. The same winter, thirty-nine resprouting trees that formed green islands in the otherwise barren environment were identified and marked. Tree growth was extraordinarily vigorous during the first year after the fire, but shoot elongation declined markedly in subsequent years. Recolonization of the 39 "islands" by the Fordinae was studied for six consecutive years. Although the life cycle of the aphids and the deciduous phenology of the tree dictate that the "islands" must be newly recolonized every year, the results of this study show that trees are persistently occupied once colonized. This is probably due to establishment of aphid colonies on the roots of secondary hosts near each tree following the first successful production of a gall. Differences in colonization success of different species could be related to both the abundance of different aphid species in the unburned forest and the biological characteristics of each aphid species.