Initial Stages in the Formation of Galls Induced by Geoica utricularia in Pistacia terebinthus Leaflets: Origin of the Two Vascular Bundles which Characterize the Wall of the Galls

Abstract

Only a few species of aphids induce galls. Among these, Paracletus cimiciformis, Forda marginata, Forda formicaria, Geoica utricularia and Baizongia pistaciae induce galls on Pistacia terebinthus leaflets. Prior to present study the au- thor examined microscopically P. terebinthus leaflets. He also studied the microscopic morphology of galls induced by the five species mentioned above. A clear microscopic difference between these galls is that in the wall of galls induced by the genera Paracletus and Forda a single vascular bundle is seen. The interpretation is that these galls are laminae of the modified leaflets. However, in the walls of the galls induced by the genera Geoica and Baizongia, two vascular bundles are observed. In the present paper a study of the early stages of development of galls produced by G. utricu- laria is described. The study was designed to explain the origin of the two vascular bundles present in the walls of these galls. The findings indicate that the aphid induces a massive development of the two vascular bundles present in the midvein of the leaflets of P. terebinthus: the main vascular bundle and the small supernumerary vascular bundle. Both these extremely developed vascular bundles occupy the walls of the galls induced by G. utricularia.