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Aspidaphis adjuvans

Wrinkly knotgrass aphid

On this page: Identification & Distribution  Biology & Ecology  Other aphids on the same host 

Identification & Distribution

Adult viviparous apterae of Aspidaphis adjuvans are elongate oval in shape, and are coloured yellowish, brownish-yellow or pale bluish green. Their antennae are short and five segmented. The apical segment of the rostrum is obtuse and short, about 0.5 times the length of the second hind tarsal segment. The dorsum is strongly granulate, wrinkly, or warty in appearance with very few short hairs. The siphunculi are short thin tubes, only 0.03-0.04 times the body length; they are swollen distally and have a subapical aperture on the inner side (cf. Aspidaphis porosiphon on Festuca rubra which has the siphunculi as small pores with partly sclerotized rims hardly raised above the body surface). The triangular cauda is covered by a cowl-like backward projection of abdominal tergite 8. The body length of adult Aspidaphis adjuvans apterae is 1.3-2.0 mm.

Our pictures below show the ovipara rather than the adult vivipara. Oviparae are yellowish brown on the anterior and posterior dorsum, and bluish-green on the mid-dorsum.

The ovipara has swollen hind tibiae the underside of which bear 20-40 rather large and well-formed circular or oval scent glands (see picture below).

The two images below show lateral and ventral views of an ovipara of Aspidaphis adjuvans in alcohol.

The clarified slide mounts below are of adult viviparous female Aspidaphis adjuvans : wingless, and winged. The alate has only a small backwardly pointing projection which does not completely cover the cauda.

Micrographs of clarified mounts  by permission of Roger Blackman, copyright AWP  all rights reserved.

Aspidaphis adjuvans lives all year round on its host, common knotgrass (Polygonum aviculare) or redshank (Persicaria maculosa). Apterous oviparae and narrow-bodied dark males are produced in autumn, with eggs laid on the senescing stems and leaves. The wrinkly knotgrass aphid has been recorded from England as well as most of continental Europe, Asia and North America.

 

Biology & Ecology

Aspidaphis adjuvans favours plants of common knotgrass (see first picture below) growing in disturbed situations on roadsides or paths. The images below show knotgrass growing on a rough farm track in East Sussex, together with a close-up of one of the tiny flowers.

We found Aspidaphis adjuvans for the first time in mid-October 2018 on the plant shown above. The knotgrass and other plants grew along the centre of a stony track between wheel ruts. The track was frequently used by vehicles and pedestrians, so the knotgrass was subjected to a certain amount of trampling.

The wrinkly knotgrass aphids were found feeding along the undersides of prostrate stems of just one knotgrass plant.

The aphids have cryptic coloration which makes them difficult to spot on the plant stem. Moreover, if disturbed, the aphids are actively cryptophilic.

They abandon their feeding sites and hide at the leaf nodes between the leaf petioles and the stem.

All the aphids we found were adult oviparae - neither adult viviparae nor immatures were present. We were also unable to find males, nor any eggs. A search of other plants for more oviparae was also unproductive.

 

Other species on the same host

Acknowledgements

We have made provisional 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).

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