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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

Population dynamics

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.

Ant attendance

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.

Natural enemies

We have not so far observed any natural enemies of Chaitophorus vitellinae, but Tomanovic et al. (2006) recorded the braconid Adialytus salicaphis as parasitizing it.

 

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.

Acknowledgements

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

  • Molnár, N. (2003). Population dynamics features of willow-feeding aphids. Acta Phytopathologica et Entomologica Hungarica 38 (1-2), 125-135. Full text

  • Molnár, N., Kovács, É. and Gallé, L. (2000). Habitat selection of ant-tended aphids on willow trees. Tiscia 32, 31-34. Full text

  • Tomanovic, Z. et al. (2006). Aphids and parasitoids on willows and poplars in southeastern Europe (Homoptera: Aphidoidea; Hymenoptera: Braconidae, Aphidiinae). Journal of Plant Diseases and Protection 113(4), 174-180. Full text