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Gorse aphidOn this page: Identification & Distribution Biology & Ecology: Ant attendance Natural enemies Other aphids on the same host
Identification & Distribution:
The apterae of Aphis ulicis are very dark blackish green but appear greyish because of the strong wax powdering (see pictures below). Their sclerotized dorsal abdominal shield may appear shiny black. The size and solidity of the dorsal shield in apterae is very variable - it may cover a large area or be greatly reduced or it may break up into irregular segmental bars or sclerites (as shown in the first micrograph below). Marginal tubercles are present on abdominal segments I and VII. The apical rostal segment is slender (more than 3 times as long as width at base) and pointed. It is narrower at its base than is the case in the very similar Aphis cytisorum. The siphunculi are dark and are 0.9-1.6 times as long the cauda. The cauda is also dark, but legs and antennae are mostly pale. The body length of Aphis ulicis apterae is 1.3-2.4 mm.
The micrographs below show an adult aptera of Aphis ulicis in ethanol, dorsal and lateral.
The alate viviparous female (see picture below) has marginal sclerites and pigmented cross bars on each segment, those on V-VII reaching to the marginal sclerites. The oviparous female is less extensively pigmented than the vivipara. The male is winged and without cross bars on tergites I-VI.
The gorse aphid is monoecious feeding only on gorse (Ulex spp.) where it forms dense colonies on shoots, flowers and green seedpods. It is usually ant attended. Sexual forms occur in autumn. Aphis ulicis is widely distributed and often common in Britain, but is otherwise only known from Spain and the Netherlands.
Biology & Ecology:
Aphis ulicis is usually, but not always, ant attended by a wide variety of ant species. It is a favourite of the southern wood ant (Formica rufa) which always attends (and defend) the species with great vigour.
The picture above shows large numbers of Formica rufa attending gorse aphids in East Sussex woodland. Other species which often attend gorse aphids are red ants (Myrmica) (see first picture below) and common black ants (Lasius niger) (see second picture below).
In northern Scotland we found it attended by either Lasius niger or (on one occasion) by Formica fusca (see picture below).
Brian et al. (1965) note that Lasius niger, Lasius alienus, Tetramorium caespitum and Formica fusca in British heathland all obtain a great deal of food in exudates from aphids, especially from Aphis ulicis and the heather aphid (Aphis callunae). We have found that colonies of Aphis ulicis appear to be more vigorously defended than colonies of Aphis callunae. Breen (1979) reports that Aphis ulicis was attended by hairy wood ants (Formica lugubris) in Ireland.
As with the broom aphid (Aphis cytisorum), rather few predators can be found attacking the colonies presumably because of the combination of attending ants and the presence of defensive chemicals in the gorse. Gorse contains quinolizidine alkaloids, high levels of which can deter even specialised gorse feeders such as the gorse weevil Exapion ulicis (Wink et al., 1982). However, alkaloid concentration seems to have no effect on infestation by Aphis ulicis possibly because, as is the case with Aphis cytisorum, the aphids are able to store quinolizidine alkaloids.
One exception to the lack of predators is the presence of cecidomyiid larvae. We have found several aphid populations with some degree of ant attendance still suffering heavy predation by Aphidoletes larvae (see pictures below).
Predatory syrphid larvae do occasionally occur, but we have only found them attacking unattended populations, such as shown the picture below of a hoverfly larva (probably Eupeodes luniger) in a gorse aphid colony in northern Scotland.
Other aphids on same host:
Blackman & Eastop list 3 species of aphid as feeding on gorse (Ulex species) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists all 3 as occurring in Britain (Show British list).