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Aphidinae : Macrosiphini : Macrosiphum willamettense
 

 

Macrosiphum willamettense

Spindly spirea aphid

On this page: Identification & Distribution Other aphids on the same host

Identification & Distribution

Adult apterae of Macrosiphum willamettense are very pale shining greenish white, with pale dusky tipped siphunculi and a pale cauda. Antennal segment III is imbricated throughout, with 1-6 secondary rhinaria limited to about the basal one third. The longest hairs on antennal segment III are 0.52-0.55 times the basal diameter of that segment (cf. Macrosiphum euphorbiae on Spiraea, where the longest hairs on segment III are 0.6-1.0 times the basal diameter of that segment). The head often has spinal tubercles, sometimes large and prominent. Antennal tubercles are large and diverging. The rostrum reaches to about the meso-coxae, with the apical rostral segment 0.74-0.97 times the second hind tarsal segment. The pronotum has large marginal tubercles and sometimes spinal ones. All first tarsal segments have 3 hairs. The abdominal tergum is uniformly, sometimes heavily sclerotized, and often lightly wrinkled throughout. Tergites II-V and sometimes I and VII have small to large, prominent marginal tubercles. The siphunculi are more or less cylindrical on the distal half (cf. Illinoia spiraecola, Illinoia spiraeae & Illinoia macgillivrayae on Spiraea, which have the siphunculi swollen on the distal third). The cauda has 7-9 hairs. The body length of adult Macrosiphum willamettense apterae is 2.3-3.5 mm. Immatures have a 'faint granular waxy sculpture'.

First image above copyright Andrew Jensen, second image copyright Epibase,
both under a creative common licence.

Alatae of Macrosiphum willamettense (not pictured) are very pale greenish white, with the siphunculi pale basally, and the apical half dusky. Antennal segment III is distinctly imbricated, with 12-17 secondary rhinaria scattered over almost the entire length of the segment.

Macrosiphum willamettense is monoecious holocyclic on its host, Spiraea douglasii. It is the only North American Macrosiphum that feeds specifically on Spiraea. Jensen (2000) notes that it is often difficult to find, even on plants that are infested. The aphids seem to prefer the freshest growth of the plants, which is often on the water sprouts around the edges of the plant patch. The plant is an inhabitant of wet places like swamps and wet meadows, but in practice the commonest place to see it is in roadside hedgerows. Macrosiphum willamettense sometimes lives together on the same plants with Illinoia spiraeae. The known distribution of this species is British Columbia, Canada and Washington and Oregon, USA.

 

Other aphids on the same host

Macrosiphum willamettense has only been recorded on 1 Spiraea species (Spiraea douglasii).

Acknowledgements

We are grateful to Andrew Jensen and Epibase for making their images of Macrosiphum willamettense and Spireae douglasii respectively available for use under a creative commons licence.

We have used the species account given by Jensen (2000), together with information from Roger Blackman & Victor Eastop in Aphids on Worlds Plants. We fully acknowledge these authors and those listed in the reference sections as the source for the (summarized) taxonomic information we have presented. Any errors in 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

  • Jensen, A.S. (2000). Eight new species of Macrosiphum from Western North America, with notes on four other poorly known species. Proceedings of the Entomological Society of Washington 102(2), 427-472. Full text