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Herb Bennet aphidOn this page: Identification & Distribution Biology & Ecology Other aphids on the same host
Identification & Distribution:
Macrosiphum gei apterae are spindle-shaped, usually mid-green to bluish green (see first picture below) or wine red (see second picture below), occasionally mauve with green mottling. The femora and siphunculi are somewhat darker at the apices. Their antennae are pale at the bases but darker towards the apices. The terminal process of antennal segment VI is 4.5-6 times the length of its base. The hairs on the dorsum of Macrosiphum gei are noticeably long (see first picture below) with the longest hair on abdominal tergite III usually more than 55 μm (cf. Macrosiphum euphorbiae for which the longest hair on abdominal tergite III is usually less than 38 µm). The siphunculi are 1.7-2.1 times the length of the cauda with reticulation on the apical 11-17%. The cauda is rather pointed and not constricted.
The Macrosiphum gei alate (see third picture above) has the head and thorax brown with indistinct marginal sclerites and dark antennae and siphunculi; there are 8-26 secondary rhinaria on the third antennal segment. Immatures (see second picture below) are green or red and may be lightly dusted with wax.
The clarified slide mounts below are of adult viviparous female Macrosiphum gei : wingless, and winged.
Macrosiphum gei is found in dense colonies on the upper parts of the flower stem of Geum urbanum (herb Bennet, wood avens). It can also occur on the undersides of the leaves of some Apiaceae, especially Anthriscus. Records of this species as a pest of potatoes result from misidentification of Macrosiphum euphorbiae as Macrosiphum gei. It is found in Europe and west Siberia and has been introduced to North America.
Biology & Ecology:
Undisturbed colonies of Macrosiphum gei, on herb bennet (see pictures below), are quite conspicuous despite their (usual) green cryptic coloration.
If the aphids are disturbed, they will actively hide by moving in amongst leaves and under the sepals.
As well as the bluish-green form, Macrosiphum gei also has a pinkish-red (magenta) form shown in the pictures below:
Other aphids on same host:
Macrosiphum gei has been recorded from 8 Geum species, and from 4 Anthriscus species (Anthriscus caucalis = A. vulgaris, Anthriscus cerefolium, Anthriscus nitida, Anthriscus sylvestris).
Blackman & Eastop list 10 species of aphid as feeding on herb Bennet (Geum urbanum) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists all 10 as occurring in Britain (Show British list).