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Genus Acaudinum

Acaudinum aphids

On this page: Genus Acaudinum Acaudinum centaureae

Acaudinum [Macrosiphini]

Acaudinum are medium-sized dark brown to blackish aphids. The head is broad and lacks antennal or median tubercles. Their antennae have a long terminal process, and both apterae and alatae have many secondary rhinaria on segment III. The main part of the dorsum is membranous, with no marginal tubercles. The siphunculi are long, tapering and dark with an indistinct flange. The cauda is very short, broad and rounded and bears numerous hairs.

Acaudinum aphids feed on knapweeds (Centaureae species) in Europe and western Asia. There are 5 species, all Palaearctic. They are attended by ants.

 

Acaudinum centaureae (Dark knapweed root aphid)

Acaudinum centaureae live at the stem base of greater knapweed (Centaurea scabiosa) where they are tented over with earth by ants (see first picture below). Adult Acaudinum centaureae apterae are shiny blackish green to black (see second picture below). The head and the antennae are dark apart from the base of antennal segment III which is reddish brown. The antennal terminal process is 5.0-6.9 times the length of the base of antennal segment VI. The apical rostral segment is 1.4-1.5 times the length of the second hind tarsal segment. The abdominal dorsum is membranous apart from a sclerite or cross band on tergite VIII and intersegmental muscle sclerites (see first micrograph below). The siphunculi are dark and bear transverse rows of very fine spicules. They are more than ten times longer than the very short broad, rounded cauda. The body length of adult Acaudinum centaureae apterae is 1.7-2.5 mm.

The alate Acaudinum centaureae (not pictured) has marginal sclerites on tergites II-IV. Its antennal terminal process is 4.5-6.0 times the length of the base of antennal segment VI, and there are 28-40 secondary rhinaria on antennal segment III. Immature aphids are brown or greenish-brown (see third picture above).

The dark knapweed root aphid feeds at the base of the leaf stalks and on the stem base and roots of the greater knapweed (Centaurea scabiosa) where it is attended by ants, often Lasius niger (see picture below). It is a characteristic species of xerothermic (=hot dry) grasslands. There is no host alternation. The aphids produce sexual forms in autumn, and the species overwinters in the egg stage. Acaudinum centaureae is found over most of Europe, including Britain, east to Russia.

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Acknowledgements

We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and sp accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). 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).

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References

  • Blackman, R.L. & Eastop, V.F. (2006). Aphids on the world's herbaceous plants and shrubs. Vols 1 and 2. John Wiley & Sons.