Stomaphis longirostris

Identification & Distribution

Adult apterae of Stomaphis longirostris (see first picture below) are elongate oval in shape and are whitish, covered with greyish wax powder. The head and prothorax are well pigmented, but the rest of the body is without sclerotization apart from the siphuncular cones, the cross band on abdominal tergite VIII, the cauda and the sub-anal and genital plates and various small sclerites. Their antennae are 1.8-2.0 mm long with 3-9 secondary rhinaria on the distal half of segment III (cf. Stomaphis graffii, where ANT III is 0.57-0.83 mm with 0-13 secondary rhinaria on its distal half); there are 4-10 rhinaria on segment IV. The terminal process is about one tenth the length of the base of antennal segment VI, with the terminal process broad and rounded. As with Stomaphis graffii, antennal segment VI is a little shorter than V (cf. Stomaphis aceris and Stomaphis takahashi on Acer in Japan, which have segment VI longer than V). The rostrum is much longer than the body. The second segment of the hind tarsus is more than 1.4 times longer than the same segment of middle tarsus (cf. Stomaphis acquerinoi & Stomaphis graffii on Acer in Europe which have that ratio less than 1.4). The Stomaphis longirostris labrum has more than 20 setae (24-31) on almost the entire length its elongated part (cf. S. graffii, S. acquerinoi, S. knechteli, which have fewer than this - but Depa & Kanturski (2014) note these setae are easily broken off). Siphuncular pores are placed on broad dark hairy cones, whose diameters range from 0.570 to 0.710 mm (cf. 0.420-0.732 mm for Stomaphis graffii). As in Stomaphis graffii, the genital plate (see ventral image of sexupara below) is divided into two (cf. Stomaphis quercus & Stomaphis wojciechowskii, which have the genital plate entire). The body length of the adult Stomaphis longirostris aptera is 6.0-6.5 mm (cf. Stomaphis graffii, which are 4.2-6.5 mm long). Immatures are similar to the adults but appear to lack any sclerotization at all.

Images above copyright Julian Hodgson, all rights reserved.

The images below show an adult aptera (dorsal) and an adult sexupara (ventral, showing cleft genital plate), photographed live on white paper.

Images above copyright Julian Hodgson, all rights reserved.

As is typical for closely ant attended aphids, Stomaphis longirostris alatae are very rare. Compared to the aptera, the alate (not pictured) is more pigmented on the head, the pro- and ptero-thorax, and the appendages. The forewings are brownish with the media forked once. Hodgson et al. (2019) suggested alates could be distinguished as follows: Stomaphis (Parastomaphis) longirostris antennal segment III with 17-20 secondary rhinaria; S. (P.) graffii ANT III with 18-27 secondary rhinaria.

Stomaphis longirostris feeds on the trunks of poplar, Populus spp., and also willow, Salix spp., (c.f. Stomaphis graffii, which feeds on maple, Acer spp.). Binazzi & Blackman (2003) identified a Stomaphis from field maple (Acer campestre) in Tuscany as Stomaphis longirostris, and Tashev (1961) identified a Stomaphis from Salix as Stomaphis graffii. However, from molecular analyses using the mitochondrial markers, Depa & Mróz (2013) found the morphological features used to distinguish Acer-feeding Stomaphis from Salix-feeding Stomaphis were unreliable, and suggested those were misidentifications. Stomaphis longirostris, Stomaphis graffii and Stomaphis wojciechowskii are usually attended by the brown ant, Lasius brunneus. Stomaphis longirostris is known from much of Europe.

 

Biology & Ecology:

Probable rediscovery in Britain

Stomaphis longirostris has long been reported to be present in Britain (see e.g. Theobald, 1929), but no specimens appear to be held by the Natural History Museum for verification, and its occurence in Britain has remained unconfirmed. In the first week of September 2021, Julian Hodgson, whilst collecting data on Stomaphis graffii on sycamore and field maple at Brampton Wood in Cambridgeshire, examined some of the many aspen (Populus tremula) trees there. After much searching, he eventually found just four Stomaphis colonies at the base of the aspen trunks deep in bark crevices, covered by ant-tenting and under a thick covering of moss. They were attended by brown ants (Lasius cf. brunneus).

Image above copyright Julian Hodgson, all rights reserved.

Given their host, and the presence of a divided genital plate (only visible on the underside, see image of sexupara above) characteristic of the subgenus Parastomaphis to which Stomaphis longirostris belongs, like Julian we are reasonably confident that these are indeed Stomaphis longirostris and not one of the other Stomaphis species. Specimens were sent to the London Natural History Museum where their identity was verified morphologically.

Life cycle

Stomaphis longirostris is a cryptic species, forming small colonies. Their fundatrices were first described by Depa & Kanturski (2014) from samples collected in mid-June. Comparing the hind- and mid-tarsal lengths of fundatrices they found HTII : MTII was 1.26–1.36, whereas those of apterous viviparae were 1.36–1.43. As noted above, a ratio below 1.40 would indicate S. graffii (Binazzi & Blackman, 2003). Depa & Kanturski suggested the following criteria for distinguishing fundatrices of the two species:

• If RIV+V/HTII > 1.64, and ANTIII/ANTIV < 2.43, and < 5 setae on extended part of labrum, then S. longirostris.
• If RIV+V/HTII < 1.61, and ANTIII/ANTIV > 2.44, and > 5 setae on extended part of labrum, then S. graffii.

Fundatrigeniae, virginogeniae (viviparae) and sexuparae of Stomaphis longirostris have more than 20, and often up to 40 setae distributed along the entire labrum.

Sexuparae and sexual morphs appear in early to mid-autumn. Like other Stomaphis, males are small, apterous and arostrate (lack mouthparts). The images below show an early-instar male and a mature male, live on white paper. The mature male was initially thought to be a fourth-instar nymph, but none of the males reared from sexuparae have moulted more than 3 times.

Images above copyright Julian Hodgson, all rights reserved.

Adult males can be readily distinguished in the field, partly because of their size, but also because they tend to climb on to the oviparae. The image below shows a male mounting an ovipara, and two others with their (pale) newly-laid eggs, plus an attending ant. Stomaphis longristris is obligatorily myrmecophilous.

Image reproduced by permission, Zdeněk Hyan via copyright Creative Commons license 4.0.

 

Other aphids on the same host

Stomaphis longirostris has been recorded on 3 species of Populus (Populus alba, Populus nigra, Populus tremula).

• Blackman & Eastop list 18 aphid species as feeding on white poplar (Populus alba) worldwide (Show World list). Of these Baker (2015) lists 7 as occurring in Britain (Show British list).

• Blackman & Eastop list 41 species of aphid as feeding on black, or Lombardy poplar (Populus nigra) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 17 as occurring in Britain (Show British list).

• Blackman & Eastop list 17 species of aphid as feeding on European aspen (Populus tremula) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 11 as occurring in Britain (Show British list).

Stomaphis longirostris has been recorded on 3 species of Salix (Salix alba, Salix caprea, Salix viminalis).

• Blackman & Eastop list over 41 species of aphids as feeding on white willow (Salix alba) (Show World list). Of these Baker (2015) lists 24 as occurring in Britain (Show British list).

• Blackman & Eastop list over 30 species of aphids as feeding on common sallow (Salix caprea) (Show World list). Of these Baker (2015) lists 24 as occurring in Britain (Show British list).

• Blackman & Eastop list 30 species of aphids as feeding on basket willow or common osier (Salix viminalis) worldwide, and provide formal identification keys (Show World list). Of these Baker (2015) lists 20 as occurring in Britain (Show British list).

Acknowledgements We are grateful to Julian Hodgson for the excellent photographs of Stomaphis longirostris feeding on the trunks of aspen trees in Cambridgeshire. We also especially thank Zdeněk Hyan for allowing us to reproduce his image of the sexuales and eggs. Provisional identifications have been made from high resolution photos of living specimens, along with host plant identity. Specimens have been sent to the Natural History Museum for verification. We have used the keys and species accounts of Binazzi & Blackman (2003) and Depa & Mróz (2013) along with Blackman & Eastop (1994), Blackman & Eastop (2006), 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 Binazzi, A & Blackman, R.L. (2003). The Acer-feeding Stomaphis with descriptions of a new species and new morphs (Hemiptera Aphididae Lachninae). Redia 86, 7-16. Google Scholar Depa, L. & and Mróz, E. (2013). Central European Acer- and Salicaceae-feeding aphids of the Genus Stomaphis (Insecta: Aphidoidea: Lachnidae) - Separate species or populations? Zoological Science 30 (6), 509-518. Full text Depa, L. and Kanturski, M. (2014). Description of hitherto unknown fundatrices of Stomaphis graffii and S. longirostris (Hemiptera, Aphididae, Lachninae). Deutsche Entomologische Zeitschrift 61(1), 31–36. Full text Hodgson J., Kaszyca-Taszakowska N., Masslowski A., Depa L. (2019). The alate morph of Stomaphis wojciechowskii - first description and implications for species ecology. Bulletin of Insectology 72(2), 233-240. Full text Tashev, D.G. (1961). Die Blattläuse (Aphidodea, Homoptera) auf Bäumen und Sträuchern in Bulgarien. Ann. Univ. Sofia. 53, 123–155. (In Bulgarian). Theobald, F.V. (1929). The plant lice or Aphididae of Great Britain. Vol. III, 364 pp.