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Identification & Distribution:

The apterae of Aphis armata are black. Immatures often have discrete wax spots, but apterae rarely have such spots. The middle abdominal tergites in apterae are usually without dark sclerotic bands. The only reliable characteristic to differentiate Aphis armata from Aphis fabae  is that the oviparae have hardly any swelling of the hind tibiae, whilst in Aphis fabae the oviparae have the hind tibiae strongly swollen. The body length of Aphis armata apterae is 2.2-2.9 mm.

 

The 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.

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

  •  Blackman, R. L. & Eastop, V. (2006). Aphids on the World's Herbaceous Plants and Shrubs. Vols 1 & 2. J. Wiley & Sons, Chichester, UK. Full text 

  •  Jacob, F.H. (1947). An account of a black aphid Doralis fabae (Scop.) subsp. armata (Hausmann), found on Digitalis purpurea L. Bulletin of Entomological Research 37(3), 431-437. 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.