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Willow stem aphidOn this page: Identification & Distribution Biology & Ecology Population dynamics Ant attendance Other aphids on the same host
Identification & Distribution
Adult apterae of Chaitophorus vitellinae are rather broad yellow-green aphids with (in life) two darker pleural longitudinal lines, but rarely with any melanic dorsal suffusion. The antennal terminal process is less than twice as long as the base of antennal segment VI. Longer antennal hairs are rather evenly distributed round the circumference of segments III-V inclusive (cf. Chaitophorus salijaponicus niger and Chaitophorus truncatus, which have them primarily on the inner side of those segments). The dorsum is normally pale sclerotic, with abdominal tergites I-VI wholly or partly fused into a rather solid carapace with dense, coarse, irregular nodular sculpturing. The apical rostral segment (RIV+V) is about 1.1-1.2 times as long as the second hind tarsal segment (HTII) and bears 4-9 subsidiary hairs. The first tarsal joints have 6-7 hairs of which one is a medioapical sense-peg. The siphunculi are pale and short. The cauda has an indentation partially delimiting the rounded apical part. The body length of adult Chaitophorus vitellinae apterae is up to 2.1 mm.
Note: one subspecies has been described, Chaitophorus vitellinae danubicus, which has a distinctly knobbed cauda and thickened dorsal hairs. It is found on white willow (Salix alba) in Romania, Czechoslovakia and Turkey.
Shown above are Chaitophorus vitellinae adult apterae, dark and pale form. The micrographs below show an adult aptera of Chaitophorus vitellinae in alcohol, dorsal and ventral.
Alatae of Chaitophorus vitellinae (not pictured) have rather narrow, evenly spaced transverse dark bands across the abdominal tergites. There are 3-10 secondary rhinaria on antennal segment III and, rarely, 1 or 2 on IV.
Chaitophorus vitellinae is found on the young twigs and leaf petioles of narrow-leafed Salix spp., especially Salix alba. They are attended by ants. There is no host alternation and the species overwinters on willow in the egg stage. Apterous males and oviparae occur in September-October. Chaitophorus vitellinae is distributed throughout Europe, and east to west Siberia, Iran and Kazakhstan.
Biology & Ecology
Molnar et al. (2003) studied the population dynamics of nine species of aphids on white willow (Salix alba) in Hungary. Among those species, Chaitophorus vitellinae represented a special type of phenology (=periodic events in their life cycle). In the spring (May) there was a low peak of abundance, numbers then decreased, but increased again to a second peak in late August to early September before declining sharply by October. For most of the summer it was the most abundant species on the willow. Analysing the relation between climate data and population dynamics of Chaitophorus vitellinae, Molnar et al. found that only temperature had a detectable effect on the numbers.
The colony we found in East Sussex was strongly ant-attended. As is often the case, it was the activity of the ants which alerted us to the presence of their colony.
Molnar et al. (2000) investigated the relationship between willow aphids and the attending ants. Out of the 10 ant species found, Lasius fuliginosus seemed to be the most important, but Lasius niger and Lasius brunneus also played a role. Aphid species differed in their dependence on ants. Mutualism between Chaitophorus vitellinae and tending ants was stronger than that for Pterocomma species. The number of Chaitophorus vitellinae on a tree was strongly affected by the presence of ants.
The ants did not leave the colony when disturbed by the photography (as happens with weak ant-aphis mutualisms). Instead they adopted threat postures as shown in the picture below.
Other aphids on the same host
Chaitophorus vitellinae occurs on 17 species of willow (Salix alba, Salix appenina, Salix babylonica, Salix caprea, Salix daphnoides, Salix fragilis, Salix iliensis, Salix kochiana, Salix micans, Salix neotricha, Salix nigricans, Salix pentandra, Salix phylicifolia, Salix purpurea, Salix triandra, Salix turanica, Salix viminalis).
Blackman & Eastop list over 120 species of aphids as feeding on willows worldwide, and provides formal identification keys for aphids on Salix.