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A new species to science?

Aphis near picridis (Horned oxtongue aphid)

On this page: Identification & Distribution  Biology & Ecology  Conclusions  Other aphids on the same host 

Identification & Distribution:

Adult apterae of this possible new species on Picris are bright yellow to yellow-green (first image below) with dark siphunculi and cauda. The antennal terminal process is 3.5-4.1 times the length of the base of segment 6 (cf. Aphis picridis  where the antennal terminal process is 2.0-2.8 longer than the base). The rostrum is very long - in two specimens 0.46 and 0.49 times the body length (cf. Aphis picridis in which the rostrum is 0.35-0.46 times the body length). There are exceptionally large prothoracic tubercles - hence the English name of horned oxtongue aphid. There are also quite large marginal tubercles on abdominal tergites 1 and 7, and also often on abdominal tergite 6 (cf. Aphis picridis which only has small marginal tubercles on tergites 1 and 7). The siphunculi are 2.2-2.3 times longer than the cauda (cf. Aphis picridis whih has the siphunculi 1.6-1.9 times longer than the cauda). (Note these data are based on only 2-3 specimens, so will underestimate the true range of variation).

The alate (see second picture above) is green rather than yellow.

We initially thought they might be Aphis nasturtii,  but (examining them in alcohol, see below) their siphunculi are dark, their siphunculi/cauda length is >2, and the rostrum extends beyond the hind coxae.

Given the features above,  and that the body colour of adult apterae (in life) is bright yellow to yellow-green (first image below), plus the alatae are green (second image below), we provisionally identified them as Aphis picridis - which has not been recorded in UK before. Perhaps the xeric roadside conditions were enabling otherwise rare species to flourish - as is probably true for the new ant species Myrmica schenckioides in the Netherlands (Boer & Noordijk, 2005 ).

On the advice of Dr. Roger Blackman we sent some alcohol-preserved specimens to the Natural History museum, from which three adult specimens were retrieved and converted to clarified mounts (one of which is shown below).

Micrograph of clarified mount  copyright Roger Blackman, all rights reserved.

These are Roger's comments:

The rostrum is very long (0.46 and 0.49 x BL) in the two that I could measure - but this could be due to small size of specimens. There are other things which differ from published descriptions; PT/base is more (3.5-4.1 versus 2.0-2.8), SIPH/CAUDA is also greater (2.2-2.3 versus 1.6-1.9), and the incidence and size of marginal tubercles is greater - the prothoracic tubercles are especially large, as is obvious in one of your photos.

[Comparing these with Aphis picridis from S. France and Italy] I don't think the differences can be explained as intraspecific variation. The size of the prothoracic tubercles is particularly noteworthy, I can't recall tubercles that size on any other Aphis. The rostrum length/body length (0.46-0.49) is greater than for similar-sized picridis, the R IV+V/HT II is greater (1.63 v 1.1-1.5), the PT/base VI is greater (3.3-4.1 v 1.5-2.8) and SIPH/CAUDA is 2.17-2.31 v 1.3-1.9.

The photo beneath is the head and prothorax your Aphis sp. under phase-contrast to show the very large prothoracic marginal tubercles. The marginal tubercles on abdominal tergite 1 and 7 are also quite large, and there are often tubercles on abdominal tergite 6, which is very unusual for an Aphis species.

I only wish we had more specimens.

Micrograph of clarified mount  of Aphis nr. picridis copyright Roger Blackman, all rights reserved.

Postcript: the hunt continues for more specimens.

 

Biology & Ecology

We found these particular aphids in a somewhat unprepossessing habitat - namely a Bedfordshire roadside-verge nature reserve, beside a lay-by, in early September.

The grass had been recently cut (earlier than it should have been, given its nature reserve status), but despite that a large colony of the aphid survived on a small oxtongue plant, Picris (= Helminthotheca) echioides (see picture below).

As with all the rare aphids we found in that small reserve (including Pterocallis maculata,  Aphis vandergooti  and Brachycaudus linariae ), they were attended by Lasius ants (see picture below).

 

Conclusions

So is this a previously undescribed species, characterized by especially large prothoracic tubercles??? We have put this on the website to ask our numerous colleagues, contributors and others if they have come across this species on Picris. We will try very hard to get more specimens next year, so that it can be properly described - and, maybe, named.

Our observations appear to be the first and only record of this Aphis species to date.
First observedby: Influential Points4 September 2015at: Clifton-Shefford bypass, Bedfordshire, UK

 

Other aphids on same host:

Blackman & Eastop list 16 species of aphid  as feeding on bristly oxtongue (Picris echioides = Helminthotheca echioides) worldwide, and provide formal identification keys. Of those aphid species, Baker (2015)  lists 14 as occurring in Britain: Brachycaudus helichrysi,  Hyperomyzus lactucae,  Hyperomyzus picridis,  Macrosiphum euphorbiae,  Myzus ornatus,  Myzus persicae,  Nasonovia ribisnigri,  Protaphis terricola,  Trama caudata, Trama maritima, Trama troglodytes,  Uroleucon picridis,  and Uroleucon sonchi. 

Acknowledgements

Our particular thanks to Paul Brown (Senior Curator, Sternorrhyncha, Natural History Museum, London,  UK) for preparing clarified slide mounts of our Aphis ? picridis from Picris echioides. Also to Roger Blackman for images of clarified slide mounts of both Aphis picridis and our Aphis from Picris - and especially for his comments regarding them (reproduced above).

Special thanks are given to Alan Outen of the Bedfordshire Invertebrate Group  who invited us to Bedfordshire to look for aphids and train some of their group in matters aphidological. He also generously accommodated us, which made the trip feasible.

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

  •  Boer, P. & Noordijk, J. (1997). Myrmica schenckioides nov. sp., a new socially parasitic ant species (Hymenoptera, Formicidae). Entomologische Berichten 65(4), 120-123.  Full text 

  •  Prieto, F.G. et al. (2004). Updated check-list of Iberian-Balearic Aphidini (Hemiptera, Aphididae). Graellsia 60(2), 197-214. Full text