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Macrosiphum equiseti (= Sitobion equiseti)Common horsetail aphidOn this page: Identification & Distribution Other aphids on the same hostIdentification & DistributionAdult apterae of Macrosiphum equiseti (see first picture below) are green or pink, with the head, legs, siphunculi and cauda dusky. Apical segments of antennae, tips of tibiae, tarsi and apices of siphunculi are frequently dark. The antennae are 0.8-1.1 times as long as the body, with the terminal process 3.5-4.5 times the base of antennal segment VI. There are 0-4 secondary rhinaria on antennal segment III, and antennal hairs are 0.3-0.4 times the basal diameter of segment III. The rostrum reaches to just past the middle coxae, and the apical rostral segment is 0.7-0.8 times the second hind tarsal segment. The dorsum is slightly sclerotic, and body hairs are short. There are marginal tubercles on the prothorax, and occasionally also on segments II-IV. The siphunculi are 0.13-0.20 times the body, and 1.1-1.5 times the cauda, with reticulation on the apical 19-20%. The cauda is not constricted, or only slightly so, and has 7-11 hairs. The cauda is 1.05-1.55 times the second hind tarsal segment (HTII) (cf. Sitobion avenae and Sitobion fragariae, which have the cauda 0.75-1.05 times HTII.) The body length of Macrosiphum equiseti apterae is 1.6-2.6 mm. Immatures (see second picture below of fourth instar) are more or less covered with a thin white wax dusting, but adults are only (lightly) waxed on the underside.
Images above copyright Anders Albrecht under a Creative Commons Attribution 3.0 License. Alate Macrosiphum equiseti (not pictured) are green or pink, with inconspicuous marginal and spinal or pleurospinal sclerites on tergites II-IV, and a cross bar on tergite VIII. Antennae are 0.7-1.1 times body length. Secondary rhinaria are distributed 4-8 on antennal segment III, 0-2 on segment IV and 0-2 on segment V. Siphunculi have reticulation on the apical 14-25%. Macrosiphum equiseti is monoecious holocyclic on horsetails (Equisetum spp.). It favours plants growing in damp, shady broad-leaved and spruce forests. The aphids feed on the stem underside, forming small groups consisting of, at most, one adult and 1-3 nymphs. The infested plants show no signs of injury. Sexuales appear during September, oviposition occurring mainly on the hostplant, sometimes on other substrates under the plant. Holman (1961) noted that most specimens he found were parasitized by Aphidius, Monoctonus or Ephedrus parasitoids. Macrosiphum equiseti occurs over most of Europe and in Canada (British Columbia). Other aphids on the same hostMacrosiphum equiseti has been recorded from 4 horsetail species (Equisetum arvense, Equisetum pratense, Equisetum sylvaticum, Equisetum telmateia).
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