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Dark spotted vetch aphidOn this page: Identification & Distribution Other aphids on the same host
Identification & Distribution
Adult Megourella tribulis apterae are dark green to black with black antennae, siphunculi and cauda. The antennal tubercles are very well-developed, with smooth, slightly concave inner margins; a median frontal tubercle is absent. The antennae are slightly longer than the body and antennal segment III bears 6-22 small secondary rhinaria approximately in a row over the basal 2/3 of its length. The terminal process is about 4.5 times as long as the base of antennal segment VI. Antennal hairs on segment III are about as long as the basal diameter of that segment. The abdomen is membranous and dorsal hairs on the metathorax and abdomen have conspicuous, well developed scleroites at their bases (cf. Megoura viciae, which has no scleroites at the bases of dorsal hairs.) The scleroites of the duplicated spinal hairs are frequently partly fused, as well as those of the marginal hairs. Conspicuous antesiphuncular sclerites are present, and tergites VII-VIII have sclerotic transverse bars. The legs are spinulose, yellowish brown to darker, with the apices of the femora and tibiae black. The siphunculi are rather thin, only very little swollen on the distal third, and attenuated towards the rather well developed flange; they are 1.5-1.7 times as long as the cauda (cf. Megoura viciae, which has siphunculi about the same length as the cauda). The cauda is triangular, slightly blunt, with 6-8 hairs. The body length of adult Megourella tribulis apterae is 2.1-2.9 mm. Immatures have a blue-grey bloom on the anterior portion of the body.
Image above by permission, copyright Dave Nicholls, NatureSpot, all rights reserved.
The alate Megourella tribulis is very like the apterous form, with the same sclerotic pattern. The antennae are much longer than the body; antennal segment III bears 26-38 rather large rhinaria not in a line along one side, and segment IV bears 3-18 rhinaria. The legs are wholly dark, or sometimes a little paler in the middle. The siphunculi are more distinctly swollen than in the aptera, and the cauda is much more slender than in apterae. The wings have normal venation, the veins are rather pale, and the two basal veins of fore wings slightly bordered with brown.
The clarified slide mounts below are of adult viviparous apterous and alate females.
Megourella tribulis are mainly found on bush vetch (Vicia sepium), although they have also been recorded from two other vetch species (see below). They feed on the base of the stem, usually at or near ground level. Despite this feeding site, they are not attended by ants. The species is monoecious holocyclic, and sexual morphs have been found in autumn. They are distributed through north-west, northern and central Europe.
Other aphids on the same host
Megourella tribulis has been recorded on 3 species of vetch (Vicia hirsuta, Vicia lutea, Vicia sepium).
Blackman & Eastop list 9 species of aphid as feeding on bush vetch (Vicia sepium) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 8 as occurring in Britain (Show British list).