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Identification & Distribution:On their primary host, Aphis sambuci apterae (see first picture below) are very variable in colour from dark green through to yellowish brown; on their secondary host Aphis sambuci are usually dark green. Adults and immatures often have white waxy stripes acros the sides of the abdominal segments. Antennae, siphunculi and legs blackish on the primary host and brownish in root colonies. The cauda is dark and bluntly tapering. The body length of adult Aphis sambuci apterae is 2.0-3.5 mm.
The dorsal abdominal sclerotic pattern comprises small marginal and postsiphuncular sclerites, dark intersegmental muscle sclerites and variably complete transverse bands across tergites 6-8. Tergites 1-4 and and 7 have marginal tubercles (visible if you expand the images below) between their dark marginal sclerites. Alates have larger postsiphunculars, well developed marginals, stronger bands on tergites 7-8 and some unpaired median dorsal sclerites.
The elder aphid normally host alternates between elder (Sambucus nigra) in spring where it forms dense colonies, and the roots and root collars of various herbs such as docks (Rumex) and campions (Silene). Sexual forms of Aphis sambuci occur in autumn. It is strongly ant attended on the primary host and sheltered by ants on the secondary host roots. It occurs throughout the northern continents.
Biology & Ecology:
The overwintering eggs are laid in the axils of buds and in cracks of the bark of elder. These hatch early in the year to give apterous fundatrices, the progeny of which are also all apterous. These give rise to very large colonies on elder.
Winged females appear in the third and subsequent generations, but no generations consist entirely of alates so colonies can be found on elder throughout the summer. The alates show a marked tendency to aggregate on the leaves (Jacob, 1949b ). The elder aphid is unusually well adapted to the urban environment, and can often be found on the young shoots of elder growing in marginal habitats such as carparks and roadsides.
Some of the alatae migrate to the secondary host, namely the roots of docks (Rumex), campions (Silene), pinks (Dianthe) and saxifrages (Saxifraga).
The picture above shows a colony of Aphis sambuci on the roots of Silene dioica (red campion).
The first picture below shows a mixture of the two main colour forms - dark green or golden brown.
The adult apterae, and sometimes the immatures, often have white waxy stripes across the sides of the abdominal segments. The immatures in the colony second-above are a lighter green with a light wax powdering (pulverulence).
Aphis sambuci is strongly attended by ants, often Lasius niger, on both the primary (see picture below) and secondary host.
On the secondary host Aphis sambuci colonies are usually tented over with earth by the ants.
The large colonies sometimes attract large numbers of predators, despite the fact that Aphis sambuci contains toxic compounds. Some predators do tend to avoid it - for example Coccinella septempunctata avoids it except just after overwintering - although it will still consume Aphis sambuci (preferentially!) in the laboratory situation (Nedved & Salvucci, 2008 ). The picture below shows an adult two-spot ladybird predating elder aphid.
It is also not uncommon to find hoverfly larvae lurking in the middle of a Aphis sambuci colony consuming them avidly.