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Permanent foxglove aphidOn this page: Identification & Distribution Biology & Ecology Other aphids on the same host
Identification & Distribution:
The adult apterae of Aphis armata are black, rarely with any white wax spots (se first picture below). The middle abdominal tergites in apterae are usually without dark sclerotic bands, but they may have a few scattered sclerites, and the largest apterae may have segmental bands. The longest hairs on the hind femora and the tibiae are about twice as long as the least width of the tibiae. The ratio of the length of the apical rostral segment (RIV+V) to the length of the second hind tarsal segment is 1.04-1.25 (cf. Aphis fabae fabae for which this ratio is 0.88-1.10). The body length of Aphis armata apterae is 2.2-2.9 mm. Immatures often have discrete wax spots.
The alatae usually have the middle abdominal tergites segmentally banded (see second picture above). The oviparae have hardly any swelling of the hind tibiae (cf. Aphis fabae sensu lato, the oviparae of which have the hind tibiae strongly swollen - this is the only reliable characteristic to differentiate Aphis armata from all the Aphis fabae subspecies).
The permanent foxglove aphid does not host alternate. Aphis armata only feeds on foxglove (Digitalis purpurea). Sexual forms occur in autumn. The species has been found in several countries in Europe, but is probably under-recorded because of difficulties in identification. Other members of the Aphis fabae complex also feed on foxglove and can only be distinguished morphologically at the ovipara stage - which is not present for most of the year.
Biology & Ecology:
Most of the photos of (hopefully) Aphis armata that we have displayed here were taken of large colonies in late May or very early June. This is on the basis that May is too early in the year for large colonies of Aphis fabae to have built up on a secondary host, and hence such colonies are most likely to be Aphis armata.
In Britain, large populations of Aphis armata can be found on Digitalis purpurea from mid May. They are usually, but not always, attended by ants most commonly by Lasius or Myrmica species.
The image below shows Aphis armata may also be attended by the southern wood ant (Formica rufa). On this occasion there were also numerous small predatory cecidomyiid larvae (Aphidoletes) amongst the aphid colony feeding on the aphids. Surprisingly, perhaps, none of the wood ants made any attempt to attack the aphid predators.
Jacob (1947) studied the ecology and food preferences of Aphis armata in northern Britain. He demonstrated that it was monoecious on foxglove and will not readily transfer to the typical crop host plants of Aphis fabae.
Other aphids on same host:
Blackman & Eastop list 11 species of aphid as feeding on foxglove (Digitalis purpurea) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 10 as occurring in Britain (Show British list).