Identification & Distribution:
Aphis euphorbiae apterae are dark blackish brown and are rather strongly wax powdered. They have a dark dorsal shield (clearly visible in the first picture below) which is confined to a rather rectangular mid-dorsal area. The cauda is rather slender and tapering. Marginal tubercles are protuberant and often present on abdominal tergite 6. Aphis euphorbiae body length is 1.7-2.1 mm.
Guest images copyright Jivko Nakev, all rights reserved.
Aphis euphorbiae alates have short bands across abdominal tergites 6-8 as well as marginal and postsiphuncular sclerites. Most of the rest of the dorsum is membranous.
Aphis euphorbiae feeds on the upper parts of the stems of Euphorbia cyparissias and a few other Euphorbia species where it is usually ant attended (see second picture above). It is usually assumed that the species produces sexual forms in autumn, but such forms have apparently not yet been described. Reproduction may therefore be entirely parthenogenetic. The spurge aphid is hardly known in Britain, but is found throughout mainland Europe, the Mediterranean basin, Africa, and South-west and Central Asia. Aphis euphorbiae has been accidentally introduced to Australia and North America.
Other aphids on same host:
Blackman & Eastop list 10 species of aphid as feeding on Bonaparte's crown (Euphorbia cyparissias) worldwide, and provide formal identification keys.
Of those aphid species, Baker (2015) lists 3 as occurring in Britain:
Jivko Nakev, 15 May 2014, Aphids on Euphorbia cyparissias - Bulgaria
Recently I spotted these aphids on Euphorbia cyparissias attended by black garden ants Lasius niger and cannot identify them. It seems to be Aphids fabae, but the host plant make me believe I am wrong.
I send you 2 photos. I would be very grateful if you help me with the Species ID.
Images copyright Jivko Nakev, all rights reserved.
The group to which they these aphids belong (Aphis spp. on Euphorbia) are described by Blackman as 'taxonomically difficult'. See aphidsonworldsplants
Nevertheless, I think it is likely your aphids are Aphis euphorbiae (or just possibly Aphis pseudopaludicola).
Blackman's description of Aphis euphorbiae is as follows:
"Apterae are blackish brown, shiny or wax-dusted, with tibiae pale brown except at apices, and siphunculi and cauda black; body length1.3-2.4 mm; siphunculi 0.70-1.37 × cauda. Dorsal abdomen with sclerotic shield usually confined to central area, not extending laterally as far as intersegmental or marginal sclerites. Cauda elongate triangular or finger-shaped, more than 1.3 × its basal width. Siphunculi rather robust, often with slightly convex sides. On upper parts of stems of Euphorbia spp., especially Euphorbia cyparissia."
The shiny sclerotic shield on the central part of the dorsum, and the rather robust siphunculi are very clear in your specimens.
We cannot however rule out Aphis pseudopaludicola. This aphid species has been recorded on the stem, petioles and undersides of leaves of Euphorbia cyparissias in Bulgaria. Aphis pseudopaludicola only differs from Aphis euphorbiae by having the hairs on the third antennal segment finely pointed, and measuring 1.1-2.0 × the basal diameter of the third antennal segment. So you would need a microscope to distinguish these two species!