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Trefoil aphidIdentification & Distribution Biology & Ecology Other aphids on Trefoil
Identification & Distribution:The aptera of Aphis coronillae is dark brown to brownish green with a more or less shiny black dorsal shield and no wax powdering. The shield extends over segments 1-6 inclusive, but is weakened by membranous lines between some of the anterior segments. The shield is reticulated, a feature formerly only thought to be visible in slide mounted specimens, but also clearly shown in our photo of the live insect (see first picture below). Abdominal tergites 1-4 and 7 regularly bear very protuberant, dome-shaped marginal tubercles. Nearly all the hairs on the legs are very short. The body length of adult Aphis coronillae apterae is 1.3-2.2 mm.
There are two subspecies with specific host-plant associations, but the morphological discriminants for the two subspecies are slight:
The aphids pictured on this page are Aphis coronillae arenariae.
Aphis coronillae lives on the basal parts of certain Leguminosae / Fabaceae, especially clovers (Trifolium) and trefoils (Medicago). It does not host alternate. Sexual forms appear in September. The males are mostly apterous, but are occasionally brachypterous or alate. Aphis coronillae is usually attended by and sheltered by ants. It is widely distributed in Europe, and is also found in west Siberia.
Biology & Ecology:
One of the main hosts of Aphis coronillae is black medick Medicago lupulina (see picture below), a very common herb found in pastures and lawns. It is a pioneer plant often growing in disturbed ground, and is especially fond of xeric habitats such as pavements in residential areas.
Despite the abundance of its host, we have (so far) only found Aphis coronillae in one location - on black medick growing in and around pavements in an East Sussex village. Its apparent scarcity is doubtless enhanced by its subterranean feeding site. The only indication of the aphids' presence is tenting with debris over infested runners by attending ants (see second picture above). The common black ant (Lasius niger) is usually the species that attends Aphis coronillae.
First and second instar Aphis coronillae (see first picture above) are yellowish-green with some reddish coloration near the siphunculi. By the third instar (see second picture above) they are a rich reddish-brown. As they develop to adults, they acquire a more-or-less shiny black dorsal shield.
The extent of this shield is somewhat variable, as can be seen in the various adults in the colony above. In the two selected adults below, the first has a well developed shield, whilst the second has it more fragmented.
Baker (2009) reports finding Aphis coronillae subspecies arenaria on subterranean parts of Medicago lupulina, growing on 'brownfield' land in Cardiff Bay during summer, 2007. It was sheltered and attended by the ant Lasius niger. There are also recent reports from Switzerland (Lethmayer, 1998 ), West Siberia (Stekolshchikov et al., 2008 ) and Greece (Tsitsipis, 2007 ).
Other aphids on Medicago lupulina:Blackman & Eastop list 10 species of aphid as feeding on Medicago lupulina worldwide, and provide formal identification keys. Of those aphid species, Baker (2015) lists 9 as occurring in Britain: Acyrthosiphon pisum, Aphis coronillae arenaria, Aphis craccivora, Aphis medicaginis, Megoura viciae, Myzus ornatus, Myzus persicae, Pemphigus populi and Therioaphis trifolii.
Bell et al. (2015) (Appendix S2) have also published an "annotated checklist of aphids present in the UK". We discuss some of the reasons for the differences between Baker's and Bell's lists in our rare aphids page.