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Uroleucon grossum = Uroleucon cichorii grossum
Large hawksbeard aphidOn this page: Identification & Distribution Biology & Ecology Other aphids on the same host
Identification & Distribution:
Apterae of Uroleucon grossum are shining metallic brown with black antennae and siphunculi, and a pale yellow cauda. Uroleucon grossum antennae are about as long as body, with the antennal terminal process 5.4-8.4 times longer than the base of the sixth antennal segment (cf. Uroleucon obscurum which has the antennal terminal process 3.8-5.3 times longer than the base of the sixth antennal segment.) The last two (fused) segments of the rostrum are 1.04 to 1.33 as long as the second tarsal segment (see micrographs below). Uroleucon grossum body hairs are placed on distinct scleroites, and there are crescent-shaped antesiphuncular sclerites (see first picture below). Their legs are mostly black, but the basal parts of the femora are pale and the middle parts of the tibiae are brown (cf. Uroleucon cichorii which have the tibiae entirely dark). The siphunculi are 1.3 to 1.7 times the length of the cauda. The caudal hairs number 19 to 33. The body length of Uroleucon grossum ranges from 2.7 to 4.4 mm.
The alate female Uroleucon grossum has rather large marginal sclerites.
For a full discussion of the joys of identifying Uroleucon species occurring on the different yellow 'daisies' (Asteraceae) see our report on aphids at Dundreggan. These species include Uroleucon hypochoeridis on Hypochaeris radicata and Leontodon autumnalis, Uroleucon cichorii on Cichorium species, Uroleucon leontodontis on Leontodon species and Uroleucon grossum on Crepis species. The latter three aphid species are often classed as subspecies of Uroleucon cichorii.
Uroleucon grossum does not host alternate but lives all year on the upper parts of stems of Crepis species. Sexual forms appear in late summer, and the species overwinters in the egg stage. Uroleucon grossum is distributed throughout Europe to Siberia and Mongolia.
Biology & Ecology:
Uroleucon aphids appear to have adapted morphologically to the different selective regimes imposed by certain characteristics of the plant surface to give rise to the large number species we see today. Members of the Asteraceae vary greatly even within a genus in trichome structure and abundance: from (smooth) glabrous surfaces (e.g. Leontodon autumnalis), to those which are densely pubescent (with short hairs), to those which have long glandular-hairs. In general the hairier the plant surface, the longer the apical segment of the aphid rostrum. Hence the use of this (size-corrected) character to differentiate species.
For our Uroleucon grossum specimens from Crepis at Dundreggan, the mean ratio of the length of the fused last two segments of the rostrum to the length of the second tarsal segment was 1.24 (SD 0.064) for n=7, well within the range for this species. For specimens on Taraxacum from East Sussex this ratio was 1.1. The mean number of caudal hairs was only 17 (SD 0.93), less than expected, but it is very difficult to count hairs accurately without doing a clarified slide mount.
We found several large colonies of the large hawksbeard aphid at Dundreggan in Scotland feeding on smooth hawk'sbeard (Crepis capillaris) (see picture of flower below) growing on waste ground.
Young nymphs of Uroleucon grossum are sometimes a deep red colour, shown below with the parent alate.
Like other Uroleucon species, Uroleucon grossum is a very active aphid and its long limbs facilitate its movement from one flower stem to another.
In East Sussex we have found green alate males on the flower stems in September (see picture below).
We have not found any parasitized specimens so far, although Tomanovicz et al. (2003) have recorded Praon yomenae, Aphidius funebris and Binodoxys centaureae parasitizing Uroleucon grossum in southeastern Europe.
Other aphids on same host:
Uroleucon grossum is known to occur on about a dozen Crepis species, plus Taraxacum officinale (dandelion).