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Genus Pterocallis [Panaphidini]
Pterocallis are small pale aphids. They have antennae that are shorter than, or as long as, the body with a short terminal process. Their siphunculi are short and truncated. In viviparae the cauda is knobbed and the anal plate is two-lobed.
There are thirteen species of the Pterocallis genus worldwide. There is no host alternation. They feed especially on alder species (Betulaceae: Alnus spp.). They are usually dispersed on the undersides of leaves, and are mostly not attended by ants (Pterocallis maculata is one exception). Wingless viviparae occur more commonly than in most genera of the Calaphidinae subfamily.
Pterocallis alni (Common alder aphid)
Both the winged and wingless adult viviparae of Pterocallis alni are yellowish white to yellowish green. Their antennae are ringed with black. Antennal segment III has only 1- 2 conspicuous hairs, with none on segments IV & V (cf. Pterocallis maculata which has conspicuous hairs on antennal segments III-V). Dorsal hairs are pale (cf. Pterocallis maculata which has dark pigmented capitate hairs situated on pale round sclerites). The hind femur has a characteristic black spot near its apex. The tarsi are black. The siphunculi have dark tips. The body length of Pterocallis alni apterae is 1.3-2.0 mm.
The alate (see second picture above) has a greenish abdomen with dark green markings and dark siphunculi.
Pterocallis alni is found almost exclusively on common alder (Alnus glutinosa) in Europe, living dispersed on undersides of leaves and sometimes attended by ants. Sexual forms occur in September-November. The common alder aphid is common and widespread in Europe, east to Turkey, Iran and Lebanon and introduced to North America, New Zealand, Australia and Chile.
Pterocallis alnifoliae (Speckled alder aphid)
All adult viviparae of Pterocallis alnifoliae are alatae (cf. Pterocallis alni, Pterocallis essigi and Pterocallis rhombifoliae, which have both apterous & alate adult viviparae). Their immatures (see first picture below) are pale greenish yellow with pale siphunculi; in the fourth instar nymph the body setae are tinged with brown. The alate adults (see second picture below) have a pale greenish yellow abdomen and darker yellow to orange head and thorax. On antennal segment III the secondary rhinaria are often confined to a pigmented area on the middle of the segment, sometimes with a few more apically (cf. Pterocallis alni, whose secondary rhinaria are confined to the basal third of segment III). The apical rostral segment (RIV+V) is 0.92-1.15 times as long as the second hind tarsal segment (HTII). The abdomen has median dorsal processes on abdominal tergites I & II, but only the one on tergite II is well-developed. The bases of their tibiae are black, as are the apical halves of the short, stump-shaped siphunculi. The anal plate is bilobed. The cauda of the adult has a clearly defined constriction, delimiting the terminal part as a knob. The body length of adult Pterocallis alnifoliae alatae is 1.3-1.7 mm.
Both images above by permission, copyright Claude Pilon, all rights reserved.
The speckled-alder aphid lives and feeds on the undersides of leaves of speckled alder (Alnus rugosa = Alnus incana rugosa) and green alder (Alnus crispa = Alnus alnobetula crispa. Oviparae and alate males occur in September-October. Pterocallis alnifoliae is found in the eastern states of the USA and in Canada.
Pterocallis maculata (Green-barred alder aphid)
Adult apterae of Pterocallis maculata are yellowish-green or green, with a pattern of diffuse dark green dorsal cross bands, giving an overall blotchy appearance (see first picture below). The antennae of Pterocallis maculata are short, only 0.6-0.8 times the body length, and have black apices to the antennal segments. Antennal segments III-V bear conspicuous hairs (see first micrograph below) (cf. Pterocallis alni which only has 1-2 conspicuous hairs on segment III). Each abdominal segment bear 5 pairs of dark pigmented capitate hairs (see second micrograph below) situated on pale round sclerites (cf. Pterocallis alni which has pale dorsal hairs). The siphunculi of Pterocallis maculata are dark, at least at the tip. There is a black spot near the apex of the hind femur and the tarsi are black. The body length of the aptera is 1.4-2.1 mm.
Second image copyright Alan Outen, all rights reserved.
The alate (see second picture above) has a pale green abdomen and dark-tipped siphunculi.
Pterocallis maculata lives in colonies along the veins (cf. Pterocallis alni which is more or less scattered) on the undersides of the leaves of alder (Alnus glutinosa and other species). It is nearly always attended by ants (cf. Pterocallis alni which is never attended by ants). Apterous males and oviparae occur in September-October. The green-barred alder aphid is quite rare in Britain, but is widely distributed in Europe, east to Turkey and Iran.