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Acyrthosiphon malvae

Geranium aphid, Pelargonium aphid

Identification & Distribution  Biology & Ecology 

Identification & Distribution:

Acyrthosiphon malvae apterae are green, yellowish or greyish green, or pinkish red, The femora and siphunculi are pale. Their siphunculi have no polygonal reticulation, are cylindrical on the distal half and are 1.8-2.2 times the pale caudal length. The terminal process of antennal segment VI is 4.8-5.8 times the length of its base. The longest hair on antennal segment III is 0.7-1.0 times the diameter of that segment and the and the apterae have 1-24 secondary rhinaria on that segment. The fused apical rostral segments are 1.1-1.4 times the second hind tarsal segment. The body length is 1.5-3.2 mm. Acyrthosiphon malvae alatae have 12-31 secondary rhinaria on antennal segment III.

 

The clarified slide mounts below are of adult viviparous female Acyrthosiphon malvae : wingless, and winged.

 

Micrographs of clarified mounts  by permission of Roger Blackman, copyright AWP  all rights reserved.

Acyrthosiphon malvae is found on many plants, but particularly herbaceous Rosaceae. There are many subspecies, mostly with specific host-plant associations.

  1. Acyrthosiphon malvae sensu stricto are pale green or red aphids on many Geraniaceae and Malvaceae worldwide, as well as plants in other families.
  2. Acyrthosiphon malvae subspecies agrimoniae is yellowish green and found in flowerheads or on undersides of leaves of Agrimonia species (agrimony) in Europe and western Asia.
  3. Acyrthosiphon malvae subspecies poterii is bright salmon pink, yellowish or green and found on Poterium sanguisorba (= Sanguisorba minor) (salad burnet), and is only known from England.
  4. Acyrthosiphon malvae subspecies potha Börner is pale yellowish or greyish green and associated with Alchemilla species (lady's mantle) throughout Europe.
  5. Acyrthosiphon malvae subspecies rogersii (Theobald) is green or yellow-green, often shiny, and may form large colonies on young leaves of Fragaria (strawberry) in north and west Europe (Blackman & Eastop 2006).

The geranium aphid does not host alternate. All subspecies spend their entire life cycles on their respective host plants, overwintering in the egg stage.

 

Biology & Ecology:

Tambs-Lyche (1975)  studied the dynamics of aphid populations on alpine tundra dry and wet meadow sites. The dominant species was Acyrthosiphon malvae subspecies potha living on Alchemilla alpina in the dry meadow and possibly on Potentilla crantzii in the wet meadow. Braschler et al. (2003)  looked at the population dynamics of aphids in experimentally fragmented grasslands in the Jura mountains in Switzerland. Acyrthosiphon malvae was one of the commonest species and was more abundant in fragmented grassland than in control plots.

The geranium aphid is fairly common in southern England on both wild and cultivated cranesbills (Geranium species) and on cultivated geraniums (Pelargonium species). All the Acyrthosiphon malvae we have found on Geranium species have been of the green form. Those below were on Geranium himalayense being grown as a garden flower.

 

A small colony was also found on cut-leaved cranesbill (Geranium dissectum) (see below).

 

We have found large colonies of the green form of Acyrthosiphon malvae on the common dovesfoot cranesbill (Geranium molle) shown below. The red forms of Acyrthosiphon malvae are less common.

 

Alford (2012)  notes that Acyrthosiphon malvae is often found in company with other species, such as Aulacorthum circumflexum. The geranium aphid also infests other ornamentals, such as Cineraria, but is rarely an important pest. Starý & Carver (1979)  reported a new species of parasitoid from Acyrthosiphon malvae living on geranium (Pelargonium) in Australia.

Acknowledgements

Our particular thanks to Roger Blackman for images of his clarified slide mounts.

Special thanks to Evelyne Turpeau for correcting our identification of an aphid that we previously had on this page. We had wrongly identified an alate Macrosiphum euphorbiae as Acyrthosiphon malvae.

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

  •  Alford, D.V. et al. (2012). Pests of ornamental trees, shrubs and flowers. 2nd Edn. Manson Publishing.

  •  Braschler, B. et al. (2003). Experimental small-scale grassland fragmentation alters aphid population dynamics. Oikos 100, 581-591. Full text 

  •  Starý, P. & Carver, M. (1979). Two new species of Aphidius Nees (Hymenoptera: Ichneumonoidea: Aphidiidae) from Australia. Journal of the Australian Entomological Society 18, 337-341. Full text 

  •  Tambs-Lyche, H. (1975). Dynamics of Aphididae populations on Hardangervidda. pp 84- in Wielgolaski, F.E. (ed) Fennoscandia Tundra Ecosystems. Springer-Verlag Berlin, Heidleberg.