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Uroleucon grossum = Uroleucon cichorii grossum

Large hawksbeard aphid

Identification & Distribution  Biology & Ecology 

Identification & Distribution:

Apterae of Uroleucon grossum are shining metallic brown with black antennae and siphunculi, and a pale yellow cauda. Their legs are mostly black, but the basal parts of the femora are pale and the middle parts of the tibiae are brown. Uroleucon grossum antennae are about as long as body. Their body length ranges from 2.7 to 4.4 mm.

 

Uroleucon grossum body hairs are placed on distinct scleroites, and there are crescent-shaped antesiphuncular sclerites (see first picture below). The ratio of the length of the siphunculi to that of the cauda is 1.3 to 1.7. The last two (fused) segments of the rostrum is 1.04 to 1.33 as long as the second tarsal segment (see second picture below). The caudal hairs number 19 to 33. 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 spp., Uroleucon leontodontis on Leontodon spp. and Uroleucon grossum on Crepis spp. The latter three aphid species are often classed as subspecies of Uroleucon cichorii.

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.

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:

For our Uroleucon grossum specimens from Dundreggan pictured here, 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. 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.

Third and fourth instar nymphs (see picture below) are a steely gray anteriorly, but with a spreading rich brown suffusion over their posterior dorsum.

 

Like other Uroleucon species, Uroleucon grossum is a very active aphid and its long limbs facilitate its movement from one flower stem to another.

We did not find any parasitized specimens at Dundreggan, although Tomanovicz et al. (2003)  have recorded Praon yomenae, Aphidius funebris, and Binodoxys centaureae parasitizing Uroleucon grossum in southeastern Europe.

Acknowledgements

We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994)  and Blackman & Eastop (2006)  supplemented with Blackman (1974) , Stroyan (1977) , Stroyan (1984) , Blackman & Eastop (1984) , Heie (1980-1995) , Dixon & Thieme (2007)  and Blackman (2010) . We fully acknowledge these authors 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).

Useful weblinks 

References

  •  Dransfield, R.D. & Brightwell, R. (2013). Aphids and their natural enemies and mutualists at Dundreggan, Scotland. Trees for Life Dundreggan estate biodiversity survey report. 105 pp. Full text 

  •  Tomanovicz, Z. et al. 2003. A review of the West Palearctic aphidiines (Hymenoptera: Braconidae: Aphidiinae) parasitic on Uroleucon spp., with the description of new species. Ann. Soc. entomolo. Fr. 39(4), 343-353.  Abstract