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Aphis polygonata (= Aphis avicularis)
Brown knotgrass aphidOn this page: Identification & Distribution Biology & Ecology Habitat Colour Ant attendance Natural enemies Other aphids on the same host
Identification & Distribution
Adult apterae of Aphis polygonata are red-brown (see first picture below) to dark brown to black. The antennal terminal process is 1.7-2.6 times the length of the base of segment VI. The abdominal dorsum is membranous without any banding of the tergites, but there are small dark intersegmental muscle sclerites and rather strong reticulation of the cuticle (which is clearly visible in the first image below). The siphunculi of Aphis polygonata are conspicuously pale and are very short and strongly tapering, being only 0.63-0.85 times the length of the cauda. The cauda is of the same colour as the siphunculi or darker and is bluntly tapering. The body length of adult apterae is 1.6-1.2 mm.
Third image above copyright Mihajlo Tomić, all rights reserved
The alate Aphis polygonata (see second image above) also has the abdominal dorsum membranous, without any banding of the tergites. The cauda of the alate is rather more pointed than that of the aptera.
Aphis polygonata is found on common knotgrass (Polygonum aviculare) and redshank (Persicaria maculosa). There is no host alternation, with sexuales produced in autumn and the population overwintering in the egg stage. Aphis polygonata is sometimes attended by ants (see third picture at top of page of colony in Serbia). In Britain Stroyan (1964) gives Berkshire, Hertford and Cornwall as the only counties where it has been found, and then mostly as trapped alatae. He suggests that perhaps Aphis polygonata needs a 'more continental climate' than that found in Britain. Our observations indicate that it is fairly widespread (perhaps common) on its host at least in south-eastern England (Kent, East Sussex, Hampshire) and probably further north and west. The brown knotgrass aphid occurs throughout Europe, North Africa, the Middle East, Central Asia and Pakistan, and has also been recorded in the USA.
Biology & Ecology
We first found this species on common knotgrass growing on a rough farm track in East Sussex. Knotgrass tends to favour ruderal (disturbed) habitats, either after natural disturbance (e.g. by wildfires) or as a result of human activities (e.g. construction sites) where it can often develop dense mats. The knotgrass and other plants grew along the centre of a stony track between wheel ruts (see picture below). The track was frequently used by vehicles and pedestrians, so the knotgrass was subjected to considerable disturbance by trampling and periodic track maintenance activities.
Large but sparsely distributed aphid colonies were found on plants along the track.
We have since found Aphis polygonata on common knotgrass growing in other disturbed habitats - on the pavements in Brockenhurst and along Highcliffe Beach, both in Hampshire. We have not, however, found this species on its other host, Persicaria maculosa despite having found many Capitophorus hippophaes on it.
The colour of Aphis polygonata is quite variable. Most of the colonies of Aphis polygonata that we have found in Britain have been a rather light red-brown (see first picture below), but some are a somewhat darker brown..
The very mottled appearance of some specimens (see second picture above) results partly from the cuticular reticulations and partly from the coating of dust particles which the aphids pick up feeding on a plant with the low-growing creeping growth habit of common knotgrass.
Some of those found in Serbia were very dark brown to black (see first picture below), more like those described by Stroyan (1984), but others were reddish-brown (see second picture below).
First image above copyright Marko Šćiban, all rights reserved.
Despite Stroyan (1984) indicating that Aphis polygonata is attended by ants, none of the colonies that we have found in southern England were attended.
Image copyright Mihajlo Tomić, all rights reserved.
However, ant-attended colonies have been found in Serbia (see picture above). In Iran Shiran et al. (2013) reported that Aphis polygonata was attended by the ant Memorium mayri.
Bugg et al. (1987) investigated whether common knotweed, a common weed in USA known to support numerous entomophagous insects, could have a use in enhancing biological control in adjoining crops. The main aphid present in the knotweed was Aphis polygonata (given as Aphis avicularis). Predatory coccinellids recorded were Hippodamia convergens, Coccinella novemnotata, and a Scymnus species. Syrphid predators recorded were Allograpta sp., Eumerus sp., Paragus tibialis, Sphaerophoria sp., and Syritta pipiens. Bugg et al. demonstrated that the mean density of aphidophagous coccinellids was much higher in knotweed than in other weed plots containing pigweed (Amaranthus graecizans) or purslane (Portulaca oleracea). However there was little evidence that this affected the number of aphidophagous coccinellids in adjoining crop plots.
In Britain we have found one of the more efficient aphid predators much used in biological control - Aphidoletes ? aphidimyza - predating Aphis polygonata (see pictures below).
These predatory larvae were present in moderate numbers attacking aphid colonies found on knotweed growing by a coastal path in Hampshire.
From the appearance of the mummy (see picture above), Lysiphlebus is the most likely identity of parasitoid we found attacking Aphis polygonata in East Sussex.
Other aphids on the same host