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Large oxtongue aphidIdentification & Distribution Biology & Ecology Other aphids on the same host
Identification & Distribution:Adult apterae of Uroleucon picridis (see first picture below) are dark shiny reddish brown, with black antennae and siphunculi. The legs are black with the basal half of the femora and middle part of tibiae light brown. The hind coxae are much paler than the distal parts of the femora. The dorsal hairs are borne on distinct scleroites, and there are also antesiphuncular sclerites and rather small marginal sclerites. The siphunculi are 1.4 to 1.7 times the length of the yellow cauda. The body length of the Uroleucon picridis adult is 2.6-3.7 mm.
The fused terminal segments of the rostrum (RIV+V) (see second picture below, and clarified mounts) are 1.45-1.84 times the length of the second hind tarsal segment (HT2) (cf. Uroleucon cichorii where RIV+V is much shorter at 1.17-1.33 times HT2.)
The images below show an adult apterous Uroleucon picridis in alcohol. The first is a dorsal view. The second is a lateral view showing the rostrum with the extended terminal segment (RIV+V).
The alate female is much like the apterous female, except that the marginal and antesiphuncular sclerites are larger. The third antennal segment has 19-23 secondary rhinaria. The ovipara is much like the viviparous female but smaller. The winged male has a slender dark green body with antennae about 1.4 times the body length.
The clarified slide mounts below are of adult viviparous female Uroleucon picridis : wingless, and winged.
The large oxtongue aphid lives on its host ox-tongue (Picris) all year round. Apterous oviparae and slender dark green males can be found in October and November. Uroleucon picridis is found in most of Europe and across Asia, but not in the Scandinavian countries nor Denmark. In Britain it is restricted to the southern counties.
Biology & Ecology:
Uroleucon picridis lives in a somewhat 'prickly' habitat, as anyone who has handled its host plant will know. The first picture below shows Picris echiodes (bristly ox-tongue) in flower.
Moran (1986) suggested that Uroleucon aphids 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. Those characteristics, including prickles, hairs, glandular hairs, scales and papillae (known collectively as trichomes) are known to affect feeding success of aphids. 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 (e.g. Leontodon hastalis). Picris echioides has both prickles (see first picture below) and extraordinary trichomes which look like miniature grappling hooks (see second picture below). See also Hyperomyzus picridis.
Moran demonstrated that the hairier the plant surface, the longer the apical segment of the aphid rostrum, and this certainly seems to apply for aphids living on Picris. Both Uroleucon picridis and Hyperomyzus picridis have longer terminal rostral segments than other members of their genus.
Adult Uroleucon seem to have no problems moving about over the host plant, but the same may be less true for the young nymphs. The picture above shows an adult apterous female giving birth to a young nymph.
After birth the youngest nymphs seem to move to what may be safer location deep in the leaf bases. These are surrounded by dense fields of trichomes which may provide protection from aphid predators.
We should also note that the hooked trichomes may not be solely (or even primarily) defensive in purpose. Picris tends to grow in amongst other plants, and such hooks enable bristly ox-tongue to cling to other plants to support it in the same way that cleavers (Galium aparine) does.
Other aphids on oxtongue (Picris):Blackman & Eastop list about 25 species of aphid as feeding on Picris echioides and Picris hieracioides worldwide, and provide formal identification keys. Of those aphid species, Baker (2015) lists 17 as occurring in Britain: Aphis craccivora, Aphis fabae, Aphis nasturtii, Aulacorthum palustre, Brachycaudus helichrysi, Hyperomyzus lactucae, Hyperomyzus picridis, Myzus ornatus, Myzus persicae, Nasonovia ribisnigri, Pemphigus bursarius Trama troglodytes Trama caudata, Trama maritima, Uroleucon cichorii, Uroleucon picridis and Uroleucon sonchi
Note: Bell et al. (2015) (Appendix S2) have also published an "annotated checklist of aphids present in the UK". We discuss some of the reasons for the differences between Baker's and Bell's lists in our rare aphids page.