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Macrosiphum gei

Herb Bennet aphid

On this page: Identification & Distribution  Biology & Ecology 

Identification & Distribution:

Macrosiphum gei apterae (see first picture below) are spindle-shaped, usually mid-green to bluish green, occasionally mauve with green mottling to wine red. The femora and siphunculi are dark 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). On abdominal tergite 3 the longest hair is usually more than 55 μm, and hairs on the head are 55-98 μm long (distinguishes from Macrosiphum euphorbiae ). 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 alate 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. The clarified slide mounts below are of adult viviparous female Macrosiphum gei : wingless, and winged.

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

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 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:

 

We have found a variety of dipterous larval predators attacking herb bennet aphid colonies (see pictures below) including cecidomyiid larvae and syrphid larvae.

 

Acknowledgements

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

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).

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