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Brachycaudus bicolor

Hound's tongue aphid

Identification & Distribution  Biology & Ecology 

Identification & Distribution:

Brachycaudus bicolor apterae (see two pictures below) are shining yellowish tinged with pink, to pale green, with separate cross bars on thoracic segments, a variably developed black patch situated dorsally on the abdomen and 2 or 3 black stripes at the tip. Their siphunculi may be pale, dusky or quite dark. The body length of apterous Brachycaudus bicolor is 2.1-2.4 mm. The light green and reddish green aphids in the photos below are likely immature Brachycaudus bicolor.

 

The hairs on abdominal tergite 8 are 30-113 μm long, much longer than the dorsal hairs on more anterior segments. Both the aptera and the alate of Brachycaudus bicolor have conspicuous flat marginal tubercles present on all segments from the pronotum to abdominal tergite 7, and spinal tubercles on the pronotum and abdominal tergites 7 and 8. These are shown in the two pictures below which are micrographs of an apterous and an alate Brachycaudus bicolor in alcohol. The marginal tubercles are especially conspicuous on the alate.

 

The alate female has 28-52 secondary rhinaria on antennal segment III, and 3-8 on segment IV.

The clarified slide mounts below are of adult viviparous female Brachycaudus bicolor: wingless (lightly sclerotized & heavily sclerotized), and winged.

   

Micrographs of clarified mounts  by permission of Roger Blackman, copyright AWP  all rights reserved.

In Britain Brachycaudus bicolor is usually found in ant-attended colonies on root collars or at the bases of leaves of Hound's tongue (Cynoglossum officinale). No sexual morphs have been recorded and the species overwinters as parthenogenetic forms. Brachycaudus bicolor has been found Britain, southern Europe, Egypt and parts of Asia.

 

Biology & Ecology:

We have only found the hound's tongue aphid on one occasion, apparently feeding on comfrey (Symphytum officinale, Boraginaceae, see picture below) on Winchelsea Beach in East Sussex.

Note we cannot be certain about the identity of the plant, since comfrey would not normally be found on a beach and the leaf shape would be abnormal for this species. Alan Outen (BIG ) suggested sea beet (Beta vulgaris) as a possibility, but the leaves are too hairy, and their venation seems wrong for that species. Any suggestions would be welcome.

The usual host of Brachycaudus bicolor in Britain is hound's tongue (Cynoglossum), but in Europe it is frequently found on a range of different genera in the Boraginaceae.

The picture above shows three adult Brachycaudus bicolor with black dorsal shields. One conspicuous behavioural feature of the species was their rapid movement into shade as soon as they were brought out into the light for photography.

All the specimens we found were living with large numbers of pale green aphids which appeared to be their immatures, although we cannot rule out the presence of a few Brachycaudus helichrysi  amongst them.

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 species 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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