Microscopic study of galls induced by three species of Geopemphigus (Hemiptera: Aphididae: Eriosomatinae) on Pistacia mexicana

The only genus of the tribe Fordini (Aphididae; Eriosomatinae) that is endemic in the American continent and that is hosted by plants of the genus Pistacia is Geopemphigus. Galls induced by the species G. morral, G. torsus and G. blackmani on Pistacia mexicana, a member of the Anacardiaceae family, were studied microscopically. The study shows characteristics shared by the three galls and specific differences, lending support to the notion that galls are the extended phenotype of gallicolous aphids. Of the three galls, G. morral shows the smallest degree of modification and the lowest cellularity, followed by G. torsus. The gall G. blackmani presents the most severe modification. On the other hand, the three galls have in common that they are not closed galls and have a multiseriate epidermis-lumen with cuticle, an interior surface without dimples, and a single vascular bundle in the wall (phloem-xylem). These common microscopic characteristics show that the genus Geopemphigus is closer to the genera Forda and Paracletus than to Baizongia.