Pemphigus nortonii Maxson, 1934.

Descriptions of this gall vary. Maxson (1934) describes galls of this species as "similar" to those of P. populicaulis. Palmer (1952) states that galls of the two species are "indistinguishable." Harper (1959a) reports that galls of the two species are "somewhat similar" but can be distinguished. Whereas galls of P nortonii are formed solely from the swelling and twisting of the petiole and open via a long, semi-spiral slit, galls of P populicaulis include tissues of both the petiole and leaf blade and open via a small round exit hole (Harper 1959a). In southern Alberta, each gall produces an average of 315 (range: 20-812) alatae, with exiting beginning in late June to mid-July and being 90% complete by August 6 (Harper 1959b).

The primary host is P deltoides (Maxson 1934; Palmer 1952; Harper 1959a). Secondary hosts have not been reported. The aphid is reported to be uncommon (Palmer 1952).

Pemphigus mortonii Maxson

Gall. Pale yellowish green. In swollen leaf base twisted on flattened and broadened petiole base; exit hole small, round orifice on underside between leaf and petiole. Size 20 mm in diameter.

Collections. On Populus sargenti in twisted petiole and leaf galls, indistinguishable from galls of P. populi-caulis. Colorado: Longmont, Dent and Fort Collins. Wyoming: Wheatland. Fundatrices and alate viviparae (fundatrigen iae) July 2 to Sept. 21; not very common.

Chief Distinguishing Characters. Character of gall (composed largely of enlarged leaf and with exit hole, a small round opening on underside between leaf and petiole),

Pemphigus nortonii Maxson

Galls on Populus deltoides especially var. occidentalis (= monilifera) are pale yellowish green, formed by a swelling at the base of the leaf lamina, twisted on the flattened, broadened petiole; resembling those of P. populicaulis (Palmer 1952), but with a long slit-like opening (Harper 1959a). Alatae emerge over an extended period (June-Sept; Harper 1959b, Grigorick & Lange 1968), migrating to an unknown secondary host. Apparently widely distributed in USA, and in Alberta, Canada. Apart from the greater number of rhinaria on ANT V and VI this species closely resembles P. junctisensoriatus. Populations from Alberta (Harper 1959a, b) seem to be intermediate in this respect, and the distinction between these two species needs to be verified.

Pemphigus nortonii, n. sp.

Described from holotype and 18 paratypes from galls taken on Populus deltoides at Wheatland, Wyoming, August 2, 1924, and July 2, 1929.

Galls: The galls are similar to those of Pemphigus populi-caulis.

Taxonomy.-This species is most closely related to Pemphigus populi-caulis, differing from it mainly in having the antennae longer in proportion to the hind tibiae and a greater number of secondary sensoria on joints III to VI of the fundatrigenia.

Pemphigus nortonii Maxson

Gall on Populus sargentii [deltoides] at junction of petiole and leaf blade with angular slit formed by twisting and swelling of petiole

Although P. nortonii was first reported from southern Alberta only four years ago, now it can be readily found on P. sargentii in shelter belts and on trees along riverbanks. As yet no secondary host has been recorded for this species.

The gall is formed on the petiole or at the junction of the leaf blade and the petiole and is produced by a swelling and twisting of the petiole only (Fig. 5). Although the gall is somewhat similar to that caused by P. populicaulis, it is generally larger, often growing to three-quarters of an inch or more in diameter. The exit from the gall is a long, semispiral slit and not a small, round opening as with P. populicaulis.

Records of the distribution of P. nortonii in Alberta are as follows: 1953, Grantham; 1957, Taber, Turin, Lethbridge, Coaldale, Populus sargentii.

This aphid was originally reported by the author in The Canadian Insect Pest Review (MacNay, 1955) as Pemphigus junctisensoriatus Maxson. Since then Maxson has checked the material and identified the aphid as P. nortonii.

Pemphigus sp. A [Russo notes that this species was formerly considered P nortonii but DNA evidence, which he does not cite, has suggested it belongs closer to P populiramulorum.]
Petiole-gall aphid
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Hosts: Populus fremontii

These galls look superficially like those of the gouty-petiole-gall aphid (P populicaulis), except that the exit hole of these galls is a spiral slit near the base of the leaf, and the galls are smooth.

Pemphigus nortoni Maxson

[Photos of three galls of this species appear on page 2 of the pdf]

P. fremonti is a host to Pemphigus nortoni Maxson

Alates of P nortoni began to emerge from their galls during May and continued to emerge until at least late July. In 1960, alates continued to emerge from 1 gall until late August.