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