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Chaitophorus salicti

Sallow leaf-vein aphid

Identification & Distribution  Biology & Ecology  Damage & Control 

Identification & Distribution:

Adult Chaitophorus salicti apterae in spring are black with a pale spinal stripe in spring, but in summer (see pictures below) are light yellowish-green with reddish-brown or greyish-black dorsal markings. Blackish specimens have a cuticular sculpture of fine wavy lines, with less conspicuous small spines than Chaitophorus niger and only rarely forming a few localized reticulations on the mesonotum and pleura of some abdominal tergites. The last two fused rostral segments (RIV+V) are 1.1 to 1.6 times the length of the second hind tarsal segment (HT2). The siphunculi are dusky or dark, and are sometimes surrounded by a membranous ring, at other times fused solidly into the dorsal carapace. Chaitophorus salicti is a small species with the body length of apterae only 1.3-1.8 mm.

 

The alates are dark, with broad dorsal abdominal cross-bands.

Sallow leaf-vein aphids live along the veins on the underside of leaves of various Sallows (Salix caprea, Salix cinerea, Salix aurita). Unlike the other Chaitophorus commonly occurring on sallows (Chaitophorus capreae ), they are usually ant-attended. 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 several sites in Britain including Flatropers Wood and Willenden/Abbots Wood in East Sussex and Oaken Wood in Surrey. The species has a very specific feeding site on sallow - namely along the deeper midveins of sallow leaves. This 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.

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 first picture below shows southern wood ants attending sallow leaf vein aphids on sallow.

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

The attending ants also 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 that 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. 

 

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

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

  •  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