Pemphigus obesinymphae

Pemphigus populitransversus

Pemphigus populitransversus [the "globular morph"]

Gall initiation by Pemphigus populitransversus was found to occur at two clearly separate times during the summer of 1975. Gall initiation is first detected as a slight swelling and bending of the petiole at the point where a fundatrix nymph has begun feeding. In this early stage, the young fundatrix is not enclosed and appears as a small black spot in the pocket formed by the swelling and bending of the petiole. Transverse galls first began forming, along with oblique galls, around May 15 on cottonwoods in the vicinity of Stony Brook. At this time, the early leaves of the tree were expanding and provided suitable sites for gall initiation. The trees were checked carefully on successive days, and after two or three days, there was no further gall initiation. Then, on June 15, more transverse galls began forming on the newly formed late leaves. This dimorphism in the timing of gall initiation resulted in a set of galls on the early leaves and a set of galls on the late leaves of the shoots. 

A dimorphism in gall shape, life history, and aphid morphology has been described for this species by Senner and Sokal (1974). The morph they refer to as "elongate" produces galls that are more elongate in shape than those of the other morph called "globular." The question immediately arose whether the presence of early and late transverse galls was related to the globular-elongate dimorphism. An analysis of the early and late transverse galls confirms the suspected relationship (Table 1). The late galls are larger than the early galls, and more spherical, as shown by the ratios of gall dimensions. The values in Table 1 resemble those of the sample from West Point, Georgia, shown in Table 3 of Senner and Sokal (1974). The early and late galls were significantly different for each character. Corroborating tests were run following methods developed by Senner and Sokal (1974). The gall dimensions and their ratios split a mixed sample of 71 galls into early and late classes fairly well. Only two galls would be misclassified by time of gall formation when the sample was split according to gall depth and only 4 galls would be so misclassified on the basis of length/width ratio. It is highly probable that the early and late galls correspond to the elongate and globular morphs, respectively. 

Pemphigus populitransversus [the "elongate morph"]

Gall initiation by Pemphigus populitransversus was found to occur at two clearly separate times during the summer of 1975. Gall initiation is first detected as a slight swelling and bending of the petiole at the point where a fundatrix nymph has begun feeding. In this early stage, the young fundatrix is not enclosed and appears as a small black spot in the pocket formed by the swelling and bending of the petiole. Transverse galls first began forming, along with oblique galls, around May 15 on cottonwoods in the vicinity of Stony Brook. At this time, the early leaves of the tree were expanding and provided suitable sites for gall initiation. The trees were checked carefully on successive days, and after two or three days, there was no further gall initiation. Then, on June 15, more transverse galls began forming on the newly formed late leaves. This dimorphism in the timing of gall initiation resulted in a set of galls on the early leaves and a set of galls on the late leaves of the shoots. 

A dimorphism in gall shape, life history, and aphid morphology has been described for this species by Senner and Sokal (1974). The morph they refer to as "elongate" produces galls that are more elongate in shape than those of the other morph called "globular." The question immediately arose whether the presence of early and late transverse galls was related to the globular-elongate dimorphism. An analysis of the early and late transverse galls confirms the suspected relationship (Table 1). The late galls are larger than the early galls, and more spherical, as shown by the ratios of gall dimensions. The values in Table 1 resemble those of the sample from West Point, Georgia, shown in Table 3 of Senner and Sokal (1974). The early and late galls were significantly different for each character. Corroborating tests were run following methods developed by Senner and Sokal (1974). The gall dimensions and their ratios split a mixed sample of 71 galls into early and late classes fairly well. Only two galls would be misclassified by time of gall formation when the sample was split according to gall depth and only 4 galls would be so misclassified on the basis of length/width ratio. It is highly probable that the early and late galls correspond to the elongate and globular morphs, respectively. 

Strategies of Gall Formation in Pemphigus Aphids