Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Identification & Distribution:Aphis salicariae apterae are reddish brown with a marked wax bloom making the aphids appear pinkish. The dorsal abdominal sclerotic pattern comprises variably complete transverse bands across tergites 6-8 and several other small sclerites. 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 images below are micrographs of an aptera (left) and an alate (right) in alcohol. Note the reddish colour of the antennae, legs and siphunculi is an artefact. The compound responsible for the reddish colour of the abdomen has dissolved in alcohol and dyed the whole insect. 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 alate has a better developed pattern with larger marginals and postsiphunculars and short median sclerites on most of the tergites.
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 (Chamerion (=Epilobium) angustifolium) where the aphid lives in colonies along the midribs of the underside of the leaves. 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:
Aphis salicariae can be very common in UK on its summer host, rosebay willowherb, resulting in extensive premature sensecence of the plants. Stroyan (1984) notes that the aphid is locally common in UK wherever its non-indigenous primary host Cornus alba is found.
On its secondary host the aphid 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 populatioons nor their persistence was affected by the presence of ants, although other aphid species were affected.
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.
We have only found the species once on its primary host - 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.