Aphis pseudocomosa

Identification & Distribution

Aphis pseudocomosa is closely related to the other black-backed aphids on Fabaceae (Aphis coronillae, Aphis craccivora and Aphis loti). Adult Aphis pseudocomosa apterae usually have a solid and extensive shiny black dorsal sclerotic shield with reticulation incorporating all the marginal sclerites (see first picture below). Smaller specimens sometimes have a more broken pattern. Unsclerotized parts are a dark warm brown. The longest hair on the third antennal segment is 0.67-1.38 times the basal diameter of that segment (cf. Aphis craccivora on which the longest hair on the third antennal segment is usually 0.37-0.75 times the basal diameter of that segment; cf. Aphis loti on which the longest hair on the third antennal segment is usually 0.40-0.71 times the basal diameter of that segment). Marginal tubercles are variable in size and distribution - when present those on tergites 2-6 are small (cf. Aphis coronillae on which there are 4-10 protuberant marginal tubercles on tergites 2-6). The cauda is tapering. Adult aptera body length is 1.52-2.29 mm. Immature Aphis pseudocomosa (see second picture below) are reddish brown to magenta with a greyish wax bloom.

The alate (not shown) has large marginal and postsiphuncular sclerites, and broad bands across tergites 6-8 or 5-8. The bands may meet with other sclerites so that the siphuncular bases are completely encircled. There is also a complete series of bands on tergites 1-4. The micrographs below show an adult apterous Aphis pseudocomosa in alcohol.

Aphis pseudocomosa lives in small colonies on the young shoots and flowers of meadow vetchling (Lathyrus pratensis). It does not host alternate, remaining all year on meadow vetchling. Apterous males and oviparae occur in autumn. Aphis pseudocomosa is (apparently) not very common in Britain, having only been previously recorded in Surrey, Essex, Hertford, Gloucester and Caernarvon, and now East Sussex. It is, however, widespread in mainland Europe into west Siberia.

Biology & Ecology

Aphis pseudocomosa was first recognised and described by Stroyan (1972). It is only found on meadow vetchling (Lathyrus pratensis), a yellow-flowered clambering plant in the Fabaceae with winged stems (see pictures below) that is found in rough grassland and roadside verges in Europe and Asia.

Attempts were made by Stroyan to transfer alatae to another member of the Fabaceae, honey clover (Melilotus alba), but no settlement or survival was recorded on this potential host.

Very little appears to have been written about this aphid species since 1972, other than occurrence records in various European countries. We have found it twice in southern England in rather different habitats. In 2014 we found it on meadow vetchling growing in deciduous woodland at Oaken Wood in Surrey. The second occurence was in 2018 on meadow vetchling growing in a hay meadow in East Sussex.

Both of these finds were in June. Colonies were generally fairly small comprising 1-10 adults with immatures (see picture above).

Ant attendance

In both locations (above) the aphids were attended by ants. In deciduous woodland the attending ant was Formica rufa (the southern wood ant, see picture below).

In the Sussex hay meadow, their attending ants belonged to a Lasius species (see two pictures below).

We have yet to observe any predators or parasitoids attacking this aphid perhaps because of the consistent attendance of the colonies by ants.

Other aphids on same host:

Blackman & Eastop list 8 species of aphid as feeding on meadow vetchling (Lathyrus pratensis) worldwide, and provide formal identification keys.

Of those aphid species, Baker (2015) lists 7 as occurring in Britain: Acyrthosiphon pisum, Aphis craccivora, Aphis pseudocomosa, Aulacorthum solani, Megoura viciae Megourella purpurea, and Pemphigus populi.

Acknowledgements Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made 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).

Useful weblinks

References Stroyan, H.L.G.et al. (1972). Additions and amendments to the check list of British aphids (Homoptera: Aphidoidea). Trans. R. ent. Soc. Lond. 124 (1), 37-79 Abstract