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Short-haired thistle aphidOn this page: Identification & Distribution Biology & Ecology
Identification & Distribution:Brachycaudus lateralis apterae (see first picture below) are green or reddish, with separate cross bars on thoracic segments, a large shining black spot situated dorsally on the abdomen and 2 or 3 black stripes at the tip. Their siphunculi are black, thick and cylindrical and 2.3-3.4 times the length of the cauda. The rostrum is long and reaches the hind coxae. The body length of apterae of Brachycaudus lateralis is 1.6-2.6 mm. Immatures (see second picture below) often have reddish patches on a greenish background.
The longest hairs on abdominal tergite 8 are 20-61 µm long, and the longest hairs on the hind femur are 10-25 μm long, much shorter than the hairs on the closely related Brachycaudus cardui. This character is used to distinguish between the species (subspecies? forms?) The results of recent DNA studies suggest that Brachycaudus lateralis should only be accorded subspecific status. The pictures below are micrographs of Brachycaudus lateralis in alcohol. The first is an adult aptera whilst the second shows the very short hairs on the femur.
The alate female (not pictured) has a dorsal patch irregularly bordered, and partly broken into crossbars and smaller sclerites. There are 18-35 secondary rhinaria on antennal segment III, and none on segment IV.
Brachycaudus lateralis is usually found close to the ground on the stems and leaves of numerous Asteraceae, including chamomile (Anthemis), thistles ( Carduus, Cirsium) and ragworts and groundsels (Senecio), where they are usually attended by ants. It usually remains on Asteraceae all year, although it has been recorded host alternating to plum (Prunus). Brachycaudus lateralis is found over most of Europe.
Biology & Ecology:
Most work on Brachycaudus lateralis has been focused upon whether it can be regarded as 'good' species distinct from Brachycaudus cardui. Remaudière & Remaudière (1997) and Heie (1992) and others regard them as two separate species. Andreev (2004) and others regard Brachycaudus lateralis as a subspecies of Brachycaudus cardui, while Eastop & Hille Ris Lambers (1976) treat Brachycaudus lateralis as a synonym of Brachycaudus cardui. More recently Coeur d'acier (2007) using molecular techniques found all their Brachycaudus cardui and Brachycaudus lateralis samples clustered together in a highly supported clade showing very small intragroup genetic distance. However the two 'species' did not form two separate clades, indicating no genetic difference. Jousselin et al. (2009), Jousselin et al. (2010) found a lack of symbiont DNA divergence between aphid specimens identified as belonging to these two 'species, and concluded that the two morphospecies, Brachycaudus cardui and Brachycaudus lateralis, may actually correspond to a single biological species.
All the colonies of Brachycaudus lateralis that we have found have been attended by ants, often tented with earth particles. This was the case for the colony on spear thistle (Cirsium vulgare) shown below.
Lasius niger was usually the species of ant attending Brachycaudus lateralis. The picture below shows this species of ant attending on lesser burdock (Arctium minus).
Colonies of Brachycaudus aphids on thistles are often heavily parasitized especially by Lysiphlebus fabarum.