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Macrosiphum dewslerPrairie flax aphidOn this page: Identification & Distribution Other aphids on the same hostIdentification & DistributionAdult apterae of Macrosiphum dewsler (see first picture below) are medium matt-green, paler along the margins and ventrally. The siphunculi are pale basally, but dusky to dark over the apical 0.5-0.8. The antennae have segments I-III and the base of IV dusky, becoming darker over the remaining segments. There are 1-10 secondary rhinaria on antennal segment III. Antennal tubercles are variably developed. There are relatively long hairs on the antennae, 0.5 or more times the basal width of antennal segment III. The rostrum reaches the meso-coxae; it has a very short apical rostral segment, 0.57-0.68 times the second hind tarsal segment, which bears 5-8 accessory hairs. The prothorax sometimes has faint marginal tubercles. Tarsi have 3 setae on segment I. The abdomen has a smooth membranous tergum, with blunt dorsal hairs. Marginal tubercles are always present on tergites I & VII, but tubercles on III-VI are only sometimes present, and are small and indistinct. The siphunculi have about 6-9 rows of apical polygonal reticulations, strong imbrications more basally, becoming smaller and ribbed or spinulate on the basal 0.25. The cauda bears 5-10 hairs. The body length of adult Macrosiphum dewsler apterae is 1.8-2.8 mm.
First image above copyright Andrew Jensen under a creative common licence; Alatae (not pictured) are medium matt-green, with thoracic plates and appendages brown. The abdomen has the tergum membranous and smooth, with small spinulate marginal sclerites on segments III-V. Oviparae are brownish orange with brown antennae, tibiae & siphunculi, and the males are winged, medium red, with the thoracic plates, appendages, siphunculi, and apex of the abdomen brown. Macrosiphum dewsler is monoecious holocyclic on its host, prairie flax (Linum lewisii) (see second picture above). This plant occurs on dry slopes and ridges, in montane coniferous forests and pinyon-juniper woodlands. The plant begins its growing season early in the spring, and is highly drought tolerant through the summer and fall. It overwinters as small above-ground shoots ready to grow immediately when conditions allow. The earliest collection of the aphid (not fundatrices) made by Jensen was 3 June 2016, so egg hatch and population establishment must have happened several weeks earlier. The aphids seem able to reproduce throughout the dry summer months, although few alatae are produced. Jensen comments that the aphid is difficult to see on Linum plant stems, as individuals feed cryptically among the leaves. Macrosiphum dewsler is known to occur in montane forest areas in Oregon, New Mexico, & North Dakota, and is also likely to occur in Arizona, California, Nevada, Utah, Arizona & Washington, USA where its host is present. Other aphids on the same hostBlackman & Eastop list only 1 species of aphid as feeding on prairie flax (Linum lewisii) worldwide. It does not occur in Britain.
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