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Identification & Distribution:

Aphis salicariae apterae are reddish brown with a marked wax bloom. The wax coating is heavier on the primary host making the aphids appear grey (see first picture below), but lighter on the secondary host so the aphids appear pinkish (see second picture below). The mid-dorsum of the Aphis salicariae aptera is more or less membranous but there are small postsiphuncular and marginal sclerites, dark intersegmental muscle sclerites and transverse bands across tergites 6-8. The siphunculi are gently to rather strongly curved outwards, and the cauda is short and bluntly tapering. The body length of Aphis salicariae apterae is 1.8-2.3 mm.

The alate Aphis salicariae (see third picture above) is much less heavily waxed than the aptera, and has a better developed pattern with larger marginals and postsiphunculars and short median sclerites on most of the tergites. As with the aptera, the siphunculi are curved outwards. The micrographs below show an aptera (first) and an alate (second) in alcohol.

The primary host of the dogwood - rosebay willowherb aphid host is the red-barked dogwood (Cornus alba) where the aphid causes leaf curl and feeds in developing flower umbels. The secondary host is rosebay willowherb (Chamaenerion (=Epilobium) angustifolium) where the aphid lives in colonies along the midribs of the underside of the leaves. It is often attended by ants. Sexual forms occur in autumn. Aphis salicariae is widely distributed through Europe into north-west and central Asia, and has been introduced to and is widepread in North America.

 

Biology & Ecology

Life cycle

The eggs of Aphis salicariae on dogwood hatch in spring, to give fundatrices which curl the leaves they are feeding on. Their offspring move to the flower umbels to give colonies of heavily waxed grey aphids.

The reddish-brown colour of these aphids is completely masked by wax in the spring generations, making them appear grey.

Mostly in the third generation, the aphids develop to alatae and migrate to their secondary host, rosebay willowherb (see picture below).

In the UK the aphids can be very common on their summer host, resulting in extensive premature sensecence of the leaves. They feed characteristically lined up along either side of the leaf midvein (see picture below).

Stroyan (1984) also notes that the aphid is locally common in UK wherever its non-indigenous primary host Cornus alba is found. Large numbers of alatae are produced, initially to disperse the populations to other secondary hosts, and later for the return migration to the primary host.

We have only once found Aphis salicariae back on its primary host in the autumn - a small group of oviparae in mid-September shown in the picture below.

Note especially the swollen hind tibia on the ovipara - each bears between 150 and 200 scent plaques which produce a sex pheromone attractive to males.

Ant attendance

The only colony we have found on the secondary host dogwood was attended (rather loosely) by Lasius ants.

On its secondary host Aphis salicariae is often ant attended as shown in the picture below where southern wood ants are tending a large colony.

Ant attendance has been studied in depth in the USA where Addicott (1979) looked at a multispecies ant aphid association on "fireweed", as rosebay willowherb is known there. In that situation neither the growth of populations nor their persistence was affected by the presence of ants, although other aphid species were affected.

Natural enemies

We have observed a variety of predators attacking Aphis salicariae colonies, including the syrphid larva shown below,

Jaskiewicz (2003) studied the phenology of Aphis salicariae (along with Anoecia corni) on its primary host Cornus alba in Poland over three years. Anoecia corni was the dominant species in all three years making up 86% to 100% of total aphid numbers. Aphis salicariae was only observed in spring and in only two of the three years. No indication is given that the species was ant attended.

 

Other aphids on same host:

Primary hosts

Aphis salicariae has been recorded from 5 Cornus species (Cornus alba, Cornus australis, Cornus mas, Cornus sanguinea, Cornus sericea).

Secondary hosts

Aphis salicariae has been recorded from 3 Epilobium species (Epilobium angustifolium, Epilobium lanceolatum, Epilobium obscurum).

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).

Useful weblinks

References

  • Addicott, J.F. (1979). A multipescies aphid-ant association: density dependence and species-specific effects. Canadian Journal of Zoology 57(3), 558-569. Abstract

  • Jaskiewicz, B. (2003). Occurence of aphids on Cornus alba L. Hortorum Cultu 2(1), 95-110. Abstract

  • Stroyan, H.L.G. (1984). Aphids - Pterocommatinae and Aphidinae (Aphidini). Handbooks for the identification of British insects. 2(6) Royal Entomological Society of London.