Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Sallow stem aphidOn this page: Identification & Distribution Biology & Ecology Discovery in Britain Ant attendance Other aphids on the same host
Identification & Distribution
Adult apterae of Chaitophorus ramicola (see first picture below) are broadly oval, mainly very dull greyish olive to black with a more-or-less distinct broad pale spinal stripe (cf. the dark form of Chaitophorus salicti, which has only a faint very narrow spinal stripe). The partially darkened cross bands on abdominal tergites I and II are separate from III, and tergites III-VI may also have separate or only partially fused bands (cf. Chaitophorus capreae, which does not have any darkened cross bands). The apical rostral segment (RIV+V) is 1.0-1.3 times as long as the second hind tarsal segment. The siphunculi are pale with darker rims, and the cauda is bluntly conical with only a slight constriction delimiting the apical part (cf. Chaitophorus salicti, which has a cauda with a distinct constriction dividing it into a triangular basal part and a globular apical knob). The body length of adult Chaitophorus ramicola apterae is 1.4-2.6 mm.
Third image above copyright Marco de Haas, all rights reserved.
Chaitophorus ramicola alates (see second picture above) are brownish olive with narrow dark dorsal abdominal cross-bands. Immature sallow stem aphids (see third picture above) are variable in colour from straw yellow to greyish olive to wine red.
The micrographs below show an adult aptera and an alate of Chaitophorus ramicola in isopropyl alcohol.
Chaitophorus ramicola feeds on the thin stems of willows (Salix species), mainly the broad-leaved species such as great sallow (Salix caprea) and grey sallow (Salix cinerea) (cf. Chaitophorus salicti, which feeds on the leaves of sallow). Chaitophorus ramicola is usually attended by ants. Sexual forms (apterous males and oviparae) develop in October. The sallow stem aphid is found in north, central and eastern Europe, Iran and Kazakhstan, and has now been found in Britain.
Biology & Ecology
Discovery in Britain
Until 2020 Chaitophorus ramicola was unrecorded in Britain - previously all our pictures of the species were generously contributed by Marco de Haas in the Netherlands. Then in July 2020 we found this aphid in Britain, on the thin stems of a sallow tree growing in a passage leading to a back garden in East Sussex (see first two pictures below).
We had found aphids on that tree previously, namely Chaitophorus salicti, a species that feeds exclusively on the leaves. The pale form of Chaitophorus salicti is shown in the third picture above. But the aphids on the stems appeared to be another related species, namely Chaitophorus ramicola, which had not previously been recorded in Britain. Reference to our past records revealed that we had in fact photographed the species on the same tree in July the previous year, but had failed to recognise it!
Key identification characters for Chaitophorus ramicola are the paler spinal stripe across the dull olive-grey tergum, separate cross bands on abdominal tergites I and II and separate or partially fused cross bands on tergites III-VI, and an apical rostral segment that is 1.0-1.3 times as long as the second hind tarsal segment.
Our specimens met these criteria with variable degrees of band separation on tergites III-VI. In the picture above one adult (centre top) had most tergites partially or wholly fused, whilst another adult (bottom left) had mainly separate tergites. They also seem to vary in the width of the pale spinal stripe - the picture below shows a group with unusually wide and prominent spinal stripes.
Blackman gives the distribution of Chaitophorus ramicola as north, central and eastern Europe and Kazakhstan - but not western or southern Europe, and the species is not included as a member of the British Chaitophorine fauna in Stroyan (1977). Given that is clearly present in Britain, we might speculate whether Chaitophorus ramicola is newly arrived, possibly as a result of global warming, or has it simply remained unobserved until now. Either is possible. There are several examples pointing to the importance of climate change. For example the northward shift in the distribution of Crypturaphis grassi from southern Europe to more northern climes including Britain has been attributed to climate change (Jansen & Warner, 2002). Similarly Piron (2013) suggested that climate change enabled the Japanese 'import' Tinocallis takachihoensis to survive winter over much of Western Europe. But it still remain true that aphids as a group are grossly 'underecorded' in Britain, compared to most other insect groups. The one thing in favour of the species being newly arrived, rather than not observed previously, is that colonies are fervently ant attended (see below) which tends to make them rather conspicuous.
The Chaitophorus ramicola colony in the Netherlands was on sallow (Salix caprea) and was attended by jet black ants (Lasius fuliginosus, see picture below).
Image above copyright Marco de Haas, all rights reserved.
The colony in Britain was attended in both years by common black ants (Lasius cf. niger), which was attending Chaitophorus salicti on leaves immediately adjacent.
Although both aphid species on the sallow tree were attended by the same ants (Lasius cf. niger), the ants' behaviour towards the two aphid species was quite different. Chaitophorus ramicola were closely tended by the ants and, if disturbed, the ants attempted to defend the colonies. Attendance of Chaitophorus salicti appeared much more cursory with the ants dispersing if disturbed. Where these two aphid speces had adjacent colonies Chaitophorus salicti were virtually unattended, either because Chaitophorus ramicola produce more melezitose or, being stem feeders, produce more honeydew.
The only study done on ant attendance of Chaitophorus ramicola was carried out by Iakovlev et al. (2017). They studied the trophic position and seasonal changes in the diet of the red wood ant Formica aquilonia as indicated by stable isotope analysis. Most aphid colonies tended by Formica aquilonia belonged to four species. The aphid species Symydobius oblongus and Chaitophorus populeti were predominant from May to September, whereas Chaitophorus ? ramicola and Aphis fabae were predominant from July to September. Honeydew collected from these four most common aphid species was probably a primary source of carbohydrate for Formica aquilonia during the summer. Tree-dwelling aphids such as Chaitophorus ramicola were found to be more important to red wood ants than grass-inhabiting aphid species like Aphis fabae.
Other aphids on same host:
Chaitophorus ramicola has been recorded on 17 species of Salix (Salix acutifolia, Salix aegyptiaca, Salix alba, Salix argyracea, Salix aurita, Salix bebbiana, Salix caprea, Salix cinerea, Salix fragilis, Salix iliensis, Salix kirilowiana, Salix phylicifolia, Salix repens, Salix rorida, Salix triandra, Salix turanica, Salix viminalis).
Blackman & Eastop list over 120 species of aphids as feeding on willows (Salix species) worldwide, and provide formal identification keys.