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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. 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. The alate (see second picture below) has a greenish abdomen with dark green markings.
Second image copyright Alan Outen, all rights reserved.
Each abdominal segment bear 5 pairs of pigmented capitate hairs (see first picture below) situated on very pale and inconspicuous round sclerites. The third antennal segment has more than 2 long hairs (see second picture below), and some hairs on the fourth and fifth antennal segment are longer than the basal diameters of their respective segments.
Pterocallis maculata lives on the undersides of the leaves of alder (Alnus glutinosa and other species) in colonies along the veins. It is nearly always 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:Blackman & Eastop list 8 species of aphids as feeding on common alder (Alnus glutinosa) worldwide, and provides formal identification keys for aphids on Alnus. Of those, Baker (2015) lists 6 aphid species as occurring in Britain: Clethrobius comes, Crypturaphis grassi, Glyphina betulae, Pterocallis alni, Pterocallis maculata and Stomaphis quercus.