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Pachypappa are medium-sized aphids with large fundatrices. The fundatrices have no wax glands, but later morphs including alatae are well endowed with wax glands. The alate spring migrants have forewings with a once-branched media vein.
There are about 13 species which host alternate between Populus (poplar) species and the roots of Picea (spruce).
Pachypappa pseudobyrsa (Poplar purse-gall aphid)
Feeding by Pachypappa pseudobyrsa fundatrices induces a small reddish-green blister-like gall (see first picture below) in the centre of the leaf near its mid-rib. This gall is open to the underside of the leaf. The fundatrix (not pictured), which lives in the gall, is yellowish olive green with a blackish head but is densely wax-covered. The fundatrix body length is 4.0-4.7 mm. She produces numerous progeny which leave the gall very soon after being born and spread out along the main veins. The leaf bearing the blister gall folds over to enclose the colony in a pseudogall. The orange immatures soon produce abundant wax which covers the aphids and the underside of the leaf (see second picture below). During May and June these immature Pachypappa pseudobyrsa develop into heavily waxed dusky-dark alatae.
Images above by permission, copyright Claude Pilon, all rights reserved.
The alate Pachypappa pseudobyrsa (see third picture above) has 5-8 secondary rhinaria with narrow sclerotic rims on antennal segment III, extending on to the proximal half of segment. The antennal terminal process is 0.17-0.21 times as long as the base of antennal segment VI. The apical rostral segment (RIV+V) is 0.60-0.75 times as long as the second hind tarsal segment (HT II) (cf. Pachypappa rosettei, whose RIV+V is 0.45-0.55 times HTII). The membrane of the forewing is without hairs (cf. Pachypappa sacculi, which has hairs on the forewing). Abdominal tergite VIII usually has a pair of well-developed wax pore plates. Siphuncular pores are absent. The genital plate has 6-12 hairs on the anterior half. The cauda has 3-5 hairs (cf. Pachypappa rosettei, which has a cauda with 10 or more hairs). The alate body is about 3.5 mm long.
Pachypappa pseudobyrsa is found on poplar (Populus) species, mainly eastern cottonwood (Populus deltoides) and quaking aspen (Populus tremuloides). Their life cycle is unknown, although it is likely that the alatae migrate to an unknown secondary host. Smith (1974), however, doubted this saying "due to the large size of the body in relation to the size and length of the wing, I question whether this species migrates. Certainly it could not be a very strong flyer because the wings are so short and delicate." Pachypappa pseudobyrsa is found in eastern North America, where it is widely distributed, and also in Colorado.
Pachypappa tremulae (Aspen-spruce aphid)
In springtime Pachypappa tremulae fundatrices (not shown here) may be found on the twigs of aspen (Populus tremula). They are unusually large (body length 5.0-6.6 mm) and are almost globular. They are a dirty reddish or yellowish brown colour, but appear silvery as they are covered with long fine hairs. They have no siphuncular pores and do not secrete any wax. The offspring of the fundatrix move on to the new shoots and form a rosette like leaf nest (see first picture below) formed by bending of the leaf petioles and stunting of growth of the shoot. The developing aphids are orange-brown in colour and they are covered in wax. One function of the wax coating of these aphids is defense against potential predators. The other major function is to coat the honeydew droplets so that they do not foul the aphid colony.
Guest images above copyright Alan Watson Featherstone all rights reserved.
These offspring all develop to winged individuals (see second picture above) which are orange or reddish brown, covered in wax and with very small siphuncular pores. They migrate in June to form colonies on the roots of spruce (Picea abies). Pachypappa tremulae apterae on spruce (not pictured) are pale yellowish white with tufts of wax posteriorly. Sexual forms then return to aspen in autumn.
Pachypappa tremulae host alternates from aspen (Populus tremula) to the roots of Norway Spuce (Picea abies). The species is widely distributed in the northern palaearctic, east to China and Japan.
Pachypappa warshavensis (Poplar leaf-nest gall aphid)
Pachypappa warshavensis forms loose leaf nest galls (see two pictures below) among leaves of white poplar (Populus alba), grey poplar (Populus canescens) or Euphrates poplar (Populus euphratica). The wingless fundatrix is reddish-brown with a body length of 3.5-4.0 mm. The offspring of the Pachypappa warshavensis fundatrix have a reddish brown abdomen - immatures are shown in the first picture below. They all develop into alates (see second picture below) with a body length of 3.0-3.2 mm.
Images copyright Dr László Érsek, all rights reserved.
A distinguishing feature of the adult Pachypappa warshavensis is the absence of small hairs on the forewing membrane (cf. Pachypappa vesicalis which has small hairs on the membrane of its forewing). Also there are 4-6 secondary rhinaria with thick sclerotic rims on the third antennal segment, often confined to the distal half of that segment.
Feeding on poplar leaves is concentrated on the petioles, which causes the leavers to fold over, thus creating a leaf nest. The alate Pachypappa warshavensis that develop in the leaf-nest are thought to migrate in June to the roots of poplar (Populus) and willow (Salix) species. Sexual forms return to poplar in autumn. Pachypappa warshavensis is found in Europe and central Asia.