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Chaitophorinae : Chaitophorini : Chaitophorus salicti
 

 

Identification & Distribution

In spring adult Chaitophorus salicti apterae are black with a faint narrow spinal stripe (see first picture below). In summer adult apterae are light yellowish-green with reddish-brown or greenish-black dorsal markings (see second picture below). The last two fused rostral segments (RIV+V) are 1.1 to 1.6 times as long as the second hind tarsal segment (HTII) (cf. Chaitophorus salijaponicus niger, which has RIV+V 0.8-1.07 times the length of HTII). Abdominal tergite I is separate from tergites II-VI, which are fused together (see micrographs of apterae in alcohol, below) (cf. Chaitophorus ramicola, which has abdominal tergite II separate from III, and tergites III-VI often have separate or partially-fused bands). The first tarsal segment normally has 5, or occasionally 6, hairs. The siphunculi are dusky or dark, and are sometimes surrounded by a membranous ring, at other times fused solidly into the dorsal carapace. The pale cauda has a distinct constriction dividing it into a triangular basal part and a globular apical knob. Chaitophorus salicti is a small species. The body length of adult apterae is only 1.3-1.8 mm.

Alatae (not pictured) are dark, with broad dorsal abdominal cross-bands. Immature Chaitophorus salicti are brownish-grey (spring form) or pale yellowish-green (summer form).

The micrographs below show dorsal views of adult apterae of the dark spring form and the pale summer form respectively in isopropyl alcohol.

Sallow leaf-vein aphids live along the veins on the underside of leaves of various sallows (including Salix caprea, Salix cinerea, Salix aurita) (cf. Chaitophorus ramicola which lives on the thinner stems of sallows. They are usually ant-attended (see third picture top) (cf. Chaitophorus capreae, which is not attended by ants). Oviparae and apterous males occur in September-October. Chaitophorus salicti occur throughout the Palaearctic region, parts of Africa, and are introduced and widespread in North America.

 

Biology & Ecology

Chaitophorus salicti is described by Stroyan (1977) as being rare in Britain. We have nevertheless found it in numerous sites in southern England including various woods (e.g. Flatropers Wood and Willenden/Abbots Wood in East Sussex and Oaken Wood in Surrey), scrub growth on industrial sites and back gardens in East Sussex.

The species prefers to feed along the deeper midveins of sallow, which provides niche-separation from Chaitophorus capreae which feeds on the shallower lateral veins. This difference in feeding position is reflected in the length of the mouthparts, which are markedly longer in Chaitophorus salicti than in Chaitophorus capreae.

Ant attendance

Shingleton et al. (2005) looked at the relationships for thirteen Chaitophorus between feeding site, length of mouthparts, escape time from predators and attendance or not by ants. Species like Chaitophorus salicti that have longer mouthparts have a longer escape time from predators because it takes longer for them to withdraw the rostrum. This makes it more worthwhile for them to 'invest' energy in attracting ants by, for example, adjusting the quality and quantity of their honeydew.

Ant tending is therefore one method of escaping interspecific competition by allowing an aphid to feed at a site unavailable to untended species. The picture below shows southern wood ants attending sallow leaf vein aphids on sallow.

The picture below shows red Myrmica ants attending sallow leaf vein aphids on sallow.

The ants seem to be very protective of this species of aphid, at least when it is the only tended species of aphid on the tree.

Natural enemies

Presumably because of ant attendance, there are usually few predators in evidence around sallow leaf vein aphid colonies.

But the attending ants do not seem to prevent parasitoids from attacking colonies. The picture below shows a colony with one mummified aphid. Others, such as the two more yellowish individuals on top of the main vein, have also been parasitized - the developing parasitoid larva visible within the aphid body as a dark mass.

The second picture above shows the parasitoid which emerged from this mummy. The wing venation (namely the lack of forewing vein M+m-cu) suggests that the parasitoid is Adialytus salicaphis, previously recorded attacking Chaitophorus on broad-leaved sallows by Tomanovic et al. (2006). This would mean that the same parasitoid attacks both Chaitophorus salicti and Chaitophorus capreae. This may well be so, but would require further taxonomic study of the specimens to confirm it.

The ants also appear not to protect the aphids from the depredations of parasitic mites (see picture below) which parasitize this species in the same way as they do to Chaitophorus populeti.

 

Other aphids on same host:

Chaitophorus salicti has been recorded from 23 Salix species.

Blackman & Eastop list over 120 species of aphids as feeding on willows (Salix species) worldwide, and provide formal identification keys.

 

Damage and control

Sallow is used for urban landscaping, and a few varieties are used for ornamental purposes, but the wood has little value. Hence there is seldom any need for control of the aphids.

Acknowledgements

Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made 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).

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References

  • Shingleton, A.W. et al. (2005). The origin of mutualism: A morphological trait promoting the evolution of ant-aphid mutualisms. Evolution 59(4), 921-926. Full text

  • Stroyan, H.L.G. (1977). Homoptera: Aphidoidea (Part) - Chaitophoridae and Callaphidae. Handbooks for the identification of British insects. 2 (4a) Royal Entomological Society of London. 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