Genus Tuberocephalus

Tuberocephalus [Macrosiphini]

Fundatrices of Tuberocephalus have 4 or 5-segmented antennae; siphunculi are present or absent, with or without a small flange. Apterous viviparae have the dorsum of the head with spinules, either sparse or dense. Antennal tubercles are finger-shaped or round, and the median frontal tubercle is indistinct or prominent. Antennae are 5- or 6-segmented, imbricated, shorter than the body, and without secondary rhinaria. The rostrum is short, at most reaching between the middle and hind coxae. The apical rostral segment is shorter or longer than the second hind tarsal segment. The legs have indistinct or distinct imbrications. The number of hairs on the first tarsal segment are 3-3-2 or 3-3-3 (fore-mid-hind). The siphunculi are cylindrical, imbricated, with the apex gradually tapering, and with or without hairs (cf. Myzus, which never have hairs on the siphunculi). The cauda is usually triangular with 4-6 hairs. Alatae have protruding, not very high antennal tubercles, secondary rhinaria on antennal segments III, IV or V, and often spino-pleural bands on the abdominal tergites; the wing veins are as normal.

There are two subgenera of Tuberocephalus that are distinct in the apterae on the secondary host. Those inhabiting leaves of Artemisia have a Phorodon-like head, whilst those inhabiting the subterranean young shoots or roots of Artemisia or Chrysanthemum have a Myzus-like head. Tuberocephalus can be distinguished from Phorodon in the absence of triommatidium, position of the projections on antennal segment I, and in the nature of siphuncular imbrications. It differs from Myzus by the ratio of the antennae to body length, and presence of hairs on the siphunculi.

There are fifteen or more species in the genus Tuberocephalus native to east Asia, often with hair-bearing siphunculi, galling the leaves of Prunus in spring. Where the life cycle is known, there is host alternation to Anthemidae (Artemisia, Chrysanthemum), where they are small aphids on growing points or undersides of leaves (subgenus Tuberocephalus) or on subterranean shoots or roots (subgenus Trichosiphoniella). On their secondary hosts these aphids look very different from the galling forms on Prunus. Most species are confined to east Asia, but three species have also been found elsewhere, namely USA (Tuberocephalus sakurae on Prunus), Italy (Tuberocephalus tianmushanensis on Prunus) and, most recently, southern England (Tuberocephalus tsengi on Artemisia).

Tuberocephalus tsengi (Oriental mugwort aphid) China, Indonesia, West Malaysia, England

The alate Tuberocephalus tsengi (see third picture above) has a black head and thorax, dark appendages and siphunculi and a light green abdomen with dark markings. The antennal tubercles are lower than in the aptera, converging apically. Antennal segment I is much thicker than II, with the inner side gibbous and rugose. The terminal process is about 2.2 times longer than the base of antennal segment VI. Secondary rhinaria are distributed 21-37 on antennal segment III, 6-10 on segment IV and none on segment V. The dorsal abdomen has marginal sclerites and broad transverse sclerites on tergites II-VII, with some partially fused to form a central patch. The siphunculi of the Tuberocephalus tsengi alate are 2.1-2.5 times as long as the cauda.

Of the Tuberocephalus species whose life cycles are known, most host alternate from Prunus primary hosts where they produce galls in spring. The galls of Tuberocephalus tsengi have yet to be found, and this species may be anholocyclic. If not, then judging by the primary hosts of related species, it is most likely to be an oriental cherry species. Their secondary hosts are Artemisia species - in UK they are only known from mugworts. Tuberocephalus tsengi occurs in China (original description as Myzus tsengi by Tao, 1963), Malaysia (BMNH collection) and Indonesia (Noordam, 2004), and probably in other countries of east and south-east Asia. Tuberocephalus tsengi also appears to be established in southern England on common mugwort (Artemisia vulgaris)(see Blackman et al., 2020). Its confusion until recently with Tuberocephalus sasakii (the species were wrongly synonomized by Eastop & Hille Ris Lambers, 1976.) means both its distribution and life cycle are uncertain.

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Acknowledgements We especially thank Roger Blackman (Natural History Museum, London) for identifing these aphids and distinguishing them from the previously-synonomised Tuberocephalus sasaki - and allowing us to reproduce some of his images. We also thank Paul Brown (Natural History Museum, London) for his help, and Rye Harbour Nature Reserve for their kind assistance and permission to sample. We have used the genus account of Su et al. (2010), together with the species account of Blackman et al., 2020. as well as 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 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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References Blackman, R.L., Brightwell, R., Dransfield, R.D. & Brown P.A. (2020). Tuberocephalus tsengi (Tao, 1963) STAT. REV. (Hemiptera: Aphididae), an East Asian Artemisia-feeding aphid species introduced to Britain. Zootaxa 4743(1): 144-150. Abstract Eastop, V.F. & Hille Ris Lambers, D. (1976). Survey of the World's Aphids. W. Junk, The Hague 573 pp. ISBN 906193561X Noordam, D. (2004). Aphids of Java, Parts V (Aphidini) and VI (Macrosiphini, Lachninae, Neophyllaphidinae, Pemphiginae). Zoologische Verhandelingen, Leiden 346, 1-212. Su, X.M. et al. (2010). Tuberocephalus (Hemiptera: Aphididae) from China with description of a new species. Oriental Insects 44, 157-191. Abstract Tao, C. C-C. (1963). Revision of Chinese Macrosiphinae (Aphidae, Homoptera). Plant Protection Bulletin (Taiwan). 5(3), 162-205. Full text