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"It has long been an axiom of mine that the little things are infinitely the most important" |
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Stomaphis longirostrisGiant aspen aphidOn this page: Identification & Distribution Biology & Ecology Possible rediscovery in Britain Life cycle Other aphids on the same hostIdentification & DistributionAdult 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 BritainStomaphis 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 are with the London Natural History Museum for morphological verification. Life cycleStomaphis 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:
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 hostStomaphis longirostris has been recorded on 3 species of Populus (Populus alba, Populus nigra, Populus tremula).
Stomaphis longirostris has been recorded on 3 species of Salix (Salix alba, Salix caprea, Salix viminalis).
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