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Aphididae : Aphidinae : Macrosiphini : Megourella
 

 

Genus Megourella

Megourella aphids

On this page: Megourella purpurea tribulis

Megourella [Macrosiphini]

Megourella are rather large, oval, swollen aphids. The head is smooth and dark with large, diverging, smooth antennal tubercles, and no median frontal tubercle. The antennae are about as long as the body with secondary rhinaria on antennal segment III in all morphs. The terminal process is 3.8-4.6 times the length of the base of antennal segment VI. The abdominal tergum in both apterae and alatae is membranous, with longitudinal rows of large spinal, marginal and pleural scleroites bearing hairs with slightly expanded apices. There are also large antesiphuncular sclerites and cross bands on the posterior tergites. The first tarsal segments of all legs have 3 hairs. The siphunculi are slightly swollen, but attenuated towards the apex, smooth or a little imbricated and sclerotic black. The cauda is elongated, shorter than the siphunculi and much paler.

Megourella aphids are similar to Megoura species, but Megoura aphids lack the dark dorsal spots. There are only two species in the genus (Megourella purpurea and Megourella tribulis). They are very similar in structure but very different in colour, and live on the stems of vetchlings (Lathyrus) and vetches (Vicia). Sexual morphs develop in autumn. Both species are found over much of Europe and in some adjoining countries.

 

Megourella purpurea (Spotted vetch aphid) Europe, Middle East

Adult apterae of Megourella purpurea (see first picture below) are dull reddish-violet or pink or occasionally dirty yellow green. They bear longitudinal rows of black spinal, pleural and marginal sclerites bearing slightly capitate hairs (cf. Megoura viciae, which are large apple green to dark bluish green aphids with no black spinal, pleural or marginal sclerites). Their antennae are black apart from right at the base of segment III, and are 1.0-1.3 times the body length with a terminal process that is 3.8-4.4 times as long as the base of segment VI. Antennal segment III bears 1-6 very small secondary rhinaria on the basal half. The apical rostral segment (RIV+V) is about as long as the length of the second hind tarsal segment (HTII). The legs are more or less dark except for the bases of the femora and tibiae. The siphunculi are black and slightly swollen, narrowing from the middle to the apex and with a small flange. The siphunculi are 1.5-1.6 times the length of the yellowish triangular cauda. The body length of adult Megourella purpurea apterae is 2.1-2.9 mm.

Alate Megourella purpurea (see second picture above) have a purple abdomen, and the head, thorax, legs and cauda are darker than in the apterae. The dorsal sclerites are more-or-less fused into cross bands on tergites I-III. Their antennae are longer than the body, and have 26-35 rather large secondary rhinaria on segment III, and 9-16 on segment IV. The siphunculi and cauda are thinner than in the apterous viviparous female. Immature Megourella purpurea are pale greenish- or pinkish-yellow with longitudinal rows of black spinal, pleural and marginal sclerites.

Megourella purpurea lives only on meadow vetchling (Lathyrus pratensis) and does not host alternate. It feeds on the basal parts of the plant usually at or near ground level. Sexual forms have not yet been observed in Britain, but oviparae and apterous males have been reared in October in the Netherlands. The spotted vetch aphid is found in most of Europe apart from the east, and extends into Iran.

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Megourella tribulis (Dark spotted vetch aphid) North-west, Northern & Central Europe

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.

First image by permission Roger Blackman, copyright AWP, all rights reserved;
Second image above by permission, copyright Dave Nicholls, NatureSpot, all rights reserved.

The alate Megourella tribulis (not pictured) 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.

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.

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Acknowledgements

We have used the keys and species accounts of Hille Ris Lambers (1949) and Blackman (2010) together with information from Roger Blackman & Victor Eastop in Aphids on Worlds Plants. We fully acknowledge these authors and those listed in the reference sections as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

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References

  • Hille Ris Lambers, G. (1949). Contributions to a monograph of the Aphididae of Europe. IV. The genera Aulacorthum Mordv., 1914; Microlophium Mordv; Hyalopteroides Theob., 1916; Idiopterus Davis, 1909; Pentalonia Coquerel, 1859; Amphorophora Buckton, 1876; Wahlgreniella nov. gen.; Megoura Buckton, 1876; Megourella nov. gen.; Hyperomyzus Borner, 1933; Nasonovia Mordv., 1914. Temminckia 8, 184-323.