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Green-barred alder aphidOn this page: Identification & Distribution Biology & Ecology Other aphids on the same host
Identification & Distribution: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 Pterocallis maculata alate (see second picture above) has a pale green abdomen and dark-tipped siphunculi.
The first micrograph below shows the long hairs on antennal segment III; the second shows the dark capitate hairs on the abdominal segments.
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.
Biology & Ecology:
Despite many years of searching alder in southern Britain, our first encounter with this aphid was when photos of it were sent to us by Alan Outen from Bedfordshire. The images below show both immature and mature alates in their characteristic position along the veins on the undersides of the leaves of common alder.
Images above copyright Alan Outen, all rights reserved.
On a later visit to Bedfordshire, we found the species ourselves on alder trees bordering a layby. Our attention was drawn to the aphid populations by the presence of Lasius ants attending the aphids. The ants were nesting between the trunk and a protective plastic cover around the tree base (used to prevent herbivores damaging young trees).
Very little seems to have been written about Pterocallis maculata, presumably reflecting its scarcity. In ornamental nurseries in Poland Labanowski & Soika (2011) found Pterocallis maculata on grey alder (Alnus incana). Only Pterocallis alni was found on common alder (Alnus glutinosa).
Other aphids on same host:
Pterocallis maculata has been recorded from 4 Alnus species (Alnus firma, Alnus fruticosa, Alnus glutinosa, Alnus incana).