Pemphigus obesinymphae

Pemphigus populitransversus

Pemphigus obesinymphae, new species

[A drawing of the gall appears on page 8 of the pdf]

Gall (Fig. 3d). The galls are formed on the petioles of late flushing leaves; most are adjacent to the leaf blade. The shape is roughly spherical, with the lips of the gall slit sometimes bulging outward. Diameters of mature galls ranged from 8 to 16 (mean 13.8). Walls of mature galls are approximately 1.5 thick. The gall slit is irregular in shape and extends along the equator of the gall for about 1/3 of the circumference, with the petiole and leaf blade at the poles. The lips remain closed along most of their length until the emergence of the adult fundatrigeniae. However, each gall has a single, round ostiole, 1.2 in diameter; this may occur anywhere along the slit. 

Material examined: All collections of P. obesinymphae were from petiole galls on Populus fremontii Watson in Arizona and Utah, USA, and were taken between 15 July 1991 and 31 July 1992. Arizona locations include: Santa Cruz County: Sonoita, Canelo (Audubon Research Ranch), Patagonia; Cochise County: Portal (Southwest Field Station); Graham County: Thatcher; Pima County: Tucson (Molino Basin, Santa Catalina Mtns.). The Utah localities include Salt Lake County: Salt Lake City (City Creek Canyon) and Davis County: Uintah (Weber River). Some alates that emerged from galls were confined in vials, and their 1 st instar offspring were obtained. 

The holotype is an alate fundatrigenia, containing embryos, collected from Populus fremontii by N. A. Moran at Patagonia on 13 October 1991. The paratypes are two adult fundatrices collected at Patagonia on 13 October 1991, two fundatrices collected at Patagonia on 8 September 1991 and 19 October 1991, one fundatrix collected at Portal on 16 September 1991, five emigrants collected at Patagonia on 25 August 1991, six emigrants collected at Patagonia on 13 October 1991, ten 1st instar fun datrigeniae, 14 2nd instar fundatrigeniae, and one 3rd instar fundatrigenia collected at Patagonia on 13 October 1991, and 12 1st instar exules deposited by emigrants collected at Patagonia on 25 August 1991. All the paratypes were collected from P. fremontii by N. A. Moran. The holotype and eight paratypes will be deposited in the U. S. National Museum, Beltsville, Maryland, U.S.A. An additional 16 paratypes will be deposited at the British Museum of Natural History, London and the Canadian National Museum. 

Pemphigus obesinymphae, n. sp. is closely related to Pemphigus knowltoni Stroyan and, especially, to Pemphigus populitransversus Riley. We hypothesize that the three constitute a monophyletic species group within the genus Pemphigus. Both P. obesinymphae and P. populitransversus form galls only on Populus fremontii, whereas P. knowltoni uses only Populus angustifolia. When adult fundatrigeniae are not present, the presence of a gall ostiole and morphological features of the 1 st and 2nd instar fundatrigeniae can be used in order to distinguish P. obesinymphae and P. populitransversus in galls on Populus fremontii (Table 1). 

[Table 1 shows that obesinymphae is known from Populus fremontii in AZ and UT and likely in NM, CO and northern Mexico, is found on petioles typically near the leaf blade, has an ostiole as well as a slit, colonizes Populus fremontii in the spring and galls late flushing leaves; that populitransversus is known from Populus fremontii throughout North America, is found near the center or elsewhere on petioles of first flush leaves, colonizes its host in fall, has no ostiole; that knowltoni is known from Populus angustifolia in UT, possibly also in ID, CO, WY, MT, galls leaf midribs, colonizes first flush leaves of its host in the fall]

Biology: The galls of P. obesinymphae contained aphids of only two generations: the fundatrix and fundatrigeniae, as is typical of Pemphigus. No apterous fundatrigeniae were found in galls of obesinymphae, although such forms are usual in both Pemphigus spirothecae Passerini and Pemphigus monophagus Maxson, other species that are known to have long-lived galls and defenders or suspected defenders (Aoki and Kurosu, 1986, 1988). The adult fundatrigeniae possessed embryos resembling typical Pemphigus exules. Therefore, this species probably alternates between two different host-plant taxa. Despite considerable searching and attempted transfers to several suspected plants (Chenopodium and Poinsettia species), its secondary hosts are yet unknown. The host alternation shows peculiar seasonal timing: fundatrigeniae fly from galls much later in the season than in other Pemphigus, overwintering occurs on secondary hosts, and sexuparae return to P. fremontii in May of the following year, after the first leaves have expanded. Sexuparae were collected from 5-20 May at Patagonia in 1992; they produced sexual offspring of typical appearance for the genus. Hatching fundatrices were collected from the same clusters of sexuales, suggesting that the eggs hatch within a short period rather than overwintering. Hatching fundatrices then establish galls on late flushing leaves; gall establishment was observed at the Patagonia site from 15 May-l June 1992. The first fundatrigeniae began to be deposited in some galls on 10 June. This life cycle recalls that of Schlechtendalia chinensis (Bell), which also produces sexuparae in spring and which also has eggs that hatch without prolonged dormancy or overwintering (Takada, 1991). 

P. obesinymphae exhibits four peculiar features: First, the life cycle is dramatically altered (Moran, 1993), with the result that galls occur only on the late leaves that expand later in the season as the shoots elongate. Most Pemphigus initiate galls on the early leaves; however, Bird et al. (1979) and Faith (1979) reported a dimorphism in the timing of gall initiation within P. populitransversus, with one gall type restricted to first flush leaves and a second restricted to late leaves. Second, 1 st instar nymphs of the 2nd generation attack predators (Moran, 1993) and have the legs well developed and the tergites heavily sclerotized. Defensive 1 st instar nymphs have been reported in Pemphigus dorocola (Aoki, 1978) and P. spirothecae (Aoki and Kurosu, 1986; Foster, 1990), but their tergites are not so strongly sclerotized as in P. obesinymphae. Third, galls have an ostiole, through which defenders enter and exit the gall (Moran, 1993). Ostioles are characteristic of galls of Pemphigus dorocola (Aoki, 1978) and P. spirothecae (Foster, 1990), but are not known from other American Pemphigus. Fourth, 2nd and 3rd instar nymphs of the 2nd generation are usually much swollen, and look as if they were wingless adults. Such swollen nymphs are not known from galls of any other Pemphigus species. Why they are so swollen remains to be investigated.

Pemphigus populitransversus

Pemphigus obesinymphae, n. sp. is closely related to Pemphigus knowltoni Stroyan and, especially, to Pemphigus populitransversus Riley. We hypothesize that the three constitute a monophyletic species group within the genus Pemphigus. Both P. obesinymphae and P. populitransversus form galls only on Populus fremontii, whereas P. knowltoni uses only Populus angustifolia. When adult fundatrigeniae are not present, the presence of a gall ostiole and morphological features of the 1 st and 2nd instar fundatrigeniae can be used in order to distinguish P. obesinymphae and P. populitransversus in galls on Populus fremontii (Table 1).

[Table 1 shows that obesinymphae is known from Populus fremontii in AZ and UT and likely in NM, CO and northern Mexico, is found on petioles typically near the leaf blade, has an ostiole as well as a slit, colonizes Populus fremontii in the spring and galls late flushing leaves; that populitransversus is known from Populus fremontii throughout North America, is found near the center or elsewhere on petioles of first flush leaves, colonizes its host in fall, has no ostiole; that knowltoni is known from Populus angustifolia in UT, possibly also in ID, CO, WY, MT, galls leaf midribs, colonizes first flush leaves of its host in the fall]

Pemphigus obesinymphae, a new American aphid species with defenders and swollen nymphs (Homoptera: Aphidoidea: Pemphigidae)