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Symydobius americanus

Dark birch aphid

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

Identification & Distribution

Adult apterae of Symydobius americanus (see first picture below) are a shiny dark brown to black in colour, and are alatoid in form as regards sclerotization. The antennae, which are as long as the body, have 2-3 white bands at the bases of segments IV-VI, and bear about 20 round secondary rhinaria distributed over the entire length of segment III (cf. Symydobius oblongus in Eurasia, which has secondary rhinaria only on the basal 0.5 of segment III). The antennal terminal process is 0.85-1.20 times as long as the base of antennal segment VI (cf. Symydobius intermedius in western USA, which has the terminal process less than 0.85 times the base of that segment). There are dark sclerotic crossbars on all the tergites. The pale siphunculi are short and truncate, somewhat broader at the base and with a flange. The cauda is broadly rounded, with no trace of a constriction.

Note: Symydobius americanus was first distinguished from the similar Eurasian species Symydobius oblongus and described under its new name by Baker (1918).

Both images above by permission, copyright Claude Pilon, all rights reserved.

The alate Symydobius americanus (see second picture above) is coloured similarly to the aptera. Antennal segment III bears about 25 rather small secondary rhinaria arranged in a row over the entire segment (cf. Symydobius oblongus in Eurasia, which has secondary rhinaria only on the basal 0.75 of segment III). The wing veins are heavily bordered with dark brown (cf. Symydobius oblongus in Eurasia, which has no dark bordering of the wing veins). There are dark sclerotic crossbars on each abdominal tergite. Young immatures (see first picture below) are reddish-brown with broader white bands on the antennae.

First image above by permission, copyright Claude Pilon, all rights reserved.
Second image above by permission, copyright Tom Murray, all rights reserved.

Symydobius americanus feeds on the stems and twigs of paper birch (Betula papyrifera). Sexual morphs occur in September-October. Like other Symydobius species, it is nearly always attended by ants. Symydobius americanus has a more northerly distribution than the only other Symydobius species in the USA (Symydobius intermedius), being found in the northern USA and Canada.

 

Other aphids on the same host

Symydobius americanus has only been recorded on one species of birch, the paper birch (Betula papyrifera).

Blackman & Eastop list 18 species of aphid as feeding on paper birch (Betula papyrifera) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 11 as occurring in Britain (Show British list).

Acknowledgements

We are grateful to Claude Pilon for pictures of Symydobius americanus (for more of her excellent pictures see). We also thank Tom Murray for permission to reproduce his picture of an ant attending a colony of Symydobius americanus (for more of his very fine pictures see).

Identification of specimens photographed by Claude Pilon was confirmed by Eric Maw by microscopic examination and DNA analysis of preserved specimens. For taxonomic details we have used the accounts of Baker (1918) and Maw et al (2000) together with Blackman & Eastop (1994) and Blackman & Eastop (2006). 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).

Useful weblinks

References

  • Baker, A.C. (1918). Our birch Symydobius distinct from the European. The Canadian Entomologist 50, 318-320. Full text