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Pellitory-of-the-wall aphidOn this page: Identification & Distribution Biology & Ecology Ant attendance Natural enemies Other aphids on the same host
Identification & Distribution
For most of the year Aphis parietariae apterae range in colour from dark to light mottled green (see first picture below). In summer pale yellowish dwarf apterae may develop (see second picture below). There is a dusting of light grey wax on the dorsum. The antennal tubercles are weakly developed. The apterae have bands across tergites 7-8 in larger specimens but the dorsum is otherwise unpigmented. The siphunculi are blackish, much darker than any other sclerotic part of the body, although the siphunculi of dwarf apterae lighten somewhat near the bases. They are 1.0-1.5 times the length of the pale cauda, which bears 6-10 hairs. The body length of Aphis parietariae apterae is 0.9-1.7 mm.
Aphis parietariae alatae (see first picture below) have marginal and postsiphuncular sclerites, and a median sclerite on tergite 6 in addition to bands on tergites VII and VII. The antennae of alates have 4-8 secondary rhinaria on the third segment, 0-2 on the fourth, and none on the fifth. Immature Aphis parietariae (see second picture below) have transverse bands of grey wax across the dorsum.
The pellitory-of-the-wall aphid does not host alternate. It lives in dense colonies on stems, under leaves and on inflorescences of Parietaria species. Sexual forms occur in autumn - the males are apterous. Aphis parietariae is found across Europe, as well as in north Africa and the Middle East.
Biology & Ecology:
Aphis parietariae normally overwinters as eggs on the host plant Parietaria judaica (pellitory-of-the-wall). However, we have found occasional apterae on plants in January (see picture below). Oviparae of Aphis parietariae have apparently not been described, so this could be an ovipara. However, it lacks the common distinguishing signs of oviparae (tibiae swollen, adomen extended), so it is more likely to be a vivipara, which would suggest there is some parthenogenetic overwintering.
We have also found established Aphis parietariae colonies as early as March in the south of England. Populations build in spring. and dense colonies may develop which can smother the plants. Those that are not attended by ants become discoloured by sooty mould.
In summer food quality declines as the plants dry out. The aphids respond to this by producing dwarf apterae (see picture below) which require little food to survive, and may actually aestivate.
In autumn sexual forms are (presumably) produced - oviparae and apterous males - and after mating, the oviparae deposit eggs on the stems of the food-plant.
Most colonies of Aphis parietariae are attended by ants, especially Lasius species, that feed on the aphid honeydew as can be seen in the picture below. The aphids benefit from the ants' presence with both contamination from honeydew and predation being reduced.
Despite the ant attendance, there may still be predation by the 'wax-protected' predator (Scymnus) shown below. Pacheco (2012) has shown experimentally that the wax on Scymnus larvae reduces intraguild predation by lacewing larvae (Chrysoperla) and presumably by ants.
Other aphids on same host:
Aphis parietariae has been recorded from 4 Parietaria species (Parietaria judaica, Parietaria lusitanica, Parietaria officinalis, Parietaria punctata) - also from Gesnouinia arborea (= Parietaria arborea) for which it is the only aphid recorded.
Blackman & Eastop list 6 species of aphid as feeding on Parietaira species worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 5 as occurring in Britain (Show British list).