Fifteen species of aphids belonging to the subfamily Fordinae (Pemphigidae, Homoptera) induce galls on wild Pistacia (Anacardiaceae) trees in Israel. In this paper I provide a summary of research on the distribution and abundance of the Fordinae in Israel, and indicate the principal ecological factors that may affect their geographical and genetical differentiation. The distribution of the Fordinae galls is primarily restricted by the ranges of their host trees, P. palaestina (8 galling species), P. atlantica (6), and P. lentiscus (1). Within these ranges, abundance of each galling species on individual trees depends on the location of the secondary host plants, on the ability of aphid spring migrants to recognize their primary host, and perhaps on genetical properties of the individual tree. Limited migratory ability of the aphids may result in genetic differentiation of geographical populations considered conspecific by morphological (taxonomical) criteria.
The dimensions of an adult insect's body parts reflect, in part, the conditions it was exposed to during the larval stages--be it nutrition, temperature, density, or other environmental constraints. Morphological differences between two genetically-similar adult morphs may reflect differences in their larval habitat. The life cycle of gall-inducing aphids (Homoptera: Pemphigidae: Fordinae) includes two winged (alate) adult morphs. The fall migrants develop in the closed galls on Pistacia and emerge as adults at the end of summer. The sexuparae develop on the roots of grasses in winter--without forming galls--and emerge as adults in the spring. The subfamily Fordinae is divided taxonomically into two tribes, Baizongiini and Fordini, which share the same life cycle. We measured 25 morphological characters on each of 156 fall migrants and 115 sexuparae, belonging to 11 species of Fordinae. We used cluster analysis to assess the morphological similarity of the species and morphs to each other. We employed conventional statistical techniques to compare the two morphs of each species, in light of the difference in larval environment of the morphs. We found, unexpectedly, that the two tribes within the Fordinae show contrasting levels of environmental control of morphology. In the Baizongiini, the sexuparae and the fall migrants of each species clustered together, implying similar morphology despite the difference in larval environment. This can be due to high heritability of the morphological characters. Not so in the Fordini: The sexuparae of all species clustered together and formed a separate cluster from the fall migrants. The sexuparae of different species are, most probably, genetically different, but experience a similar larval environment that is ecologically different from the gall environment of the fall migrants. The larval environment seems to have an overriding effect over any other factors--genetic or otherwise--controlling the expression of adult morphological characters in this tribe.
The aphid Slavum wertheimae HRL (Homoptera; Pemphigidae, Fordinae) is monoecious on its host tree, Pistacia atlantica (Anacardiaceae). S. wertheimae induces large, conspicuous, coral-shaped “cauliflower” galls and is very abundant on some trees, while rare or absent on others nearby. It is the only species among Israeli Fordinae which does not alternate between host plants. We investigated the changes in gall size, and in clone size of their aphid inhabitants, from 1994 to 1996, in order to understand the causes of differential herbivory. Gall abundance on male and female trees was similar, but galls on male trees were larger and contained twice as many aphids as those on female trees, suggesting sex-dependent resource allocation in the host plant. Trees heavily galled in 1994 were recolonized in 1995 and 1996, while other trees nearby remained uncolonized. Similarly, within galled trees, shoots on branches carrying old galls were more likely to be freshly galled than shoots on previously ungalled branches. Alate sexuparae were trapped on ungalled P. atlantica trees in smaller numbers than on galled trees (none were trapped on non-host trees). Differential herbivory in S. wertheimae may be explained in part by the behavior of the alates, which may not wander far from their natal trees. Budburst (but not leaf abscission) times were correlated with gall abundance on the same trees.
Forda formicaria von Heyden is one of the most common galling aphids on Pistacia palaestina in Israel. We report here on the distribution of the galls on shoots and leaves of the host tree. Using three indices of gall abundance, we illustrate changes in abundance of the characteristic crescent-shaped final galls on individual trees at one site from one year to the next. We describe the pattern of temporal changes in clone size within galls during the summer. Although the galls reach their final size shortly after gall induction, when they contain the single fundatrix nymph only, tissue differentiation in the gall wall continues throughout the summer, apparently due to stimulation by the increasing aphid clone.