Patch Size and Patch Quality of Gall-inducing Aphids in a Mosaic Landscape in Israel

For weak flying insects feeding on two different host plants during their life cycle, such as gall-inducing aphids, patch and matrix characteristics may play a critical role in patch occupancy and population size in occupied patches. The aims of the present study were to define the basic patch size of Baizongia pistaciae (L) (Aphididae, Fordini), an aphid inducing galls on Pistacia palaestina Boiss (Anacardiaceae) using a genetic approach, and to estimate the impact of landscape structure and patch quality on patch occupancy and gall density on occupied trees of this aphid and four other closely related species. Using 42 genetic markers detected by RAPD-PCR in 117 clones of the galling aphid Baizongia pistaciae, we calculated Wright's F statistics and estimated the number of winged migrants between demes. We found that host trees at least 150 m apart supported genetically differentiated demes of B. pistaciae, and formed distinct patches. Since the annual cycle of this aphid involves alternation between two different hosts, P. palaestina trees and Poaceae roots, patch – the smallest area that sustains a deme – is a relatively small area that must be composed of at least a single P. palaestina tree and nearby secondary hosts. To assess the impact of landscape structure and patch quality on patch occupancy and gall abundance in occupied patches, two field surveys of P. palaestina trees in natural Mediterranean maquis were performed. Among the five species of gall-inducing aphids found, B. pistaciae was the most abundant of those surveyed. Host trees were occupied more often in the ecotone, the transition zone between Mediterranean closed maquis and open bata, than in the maquis. Mature and old trees were more often occupied than young ones, and shrubs more often than tree-like plants. There was no difference in the proportion of occupied trees between isolated host trees or those growing in groups. Species richness showed similar trends. We also found no significant differences in gall abundance in occupied trees among tree quality categories, except that trees growing in the ecotone tended to carry more galls than those growing in the maquis. In conclusion, the best patch of gall-inducing aphids seems to be a small area, composed of an old shrub of P. palaestina standing in an open landscape with nearby secondary hosts, grass roots, available for colonization by winged migrants.