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Aphis evonymi
(= Aphis euonymi = Aphis fabae evonymi)

Spindle aphid

Identification & Distribution  Biology & Ecology  Other aphids on the same host  Damage & Control 

Identification & Distribution:

The adult aptera of Aphis evonymi (see first picture below) is a reddish- to chocolate-brown with broad dark sclerotic bands across the pronotum and mesonotum, and narrower ones across abdominal tergites 7-8. It consistently lacks marginal tubercles on abdominal tergites 2-4 (cf. the similarly coloured Aphis ilicis  and Aphis viburni  which tend to have marginal tubercles on abdominal tergites 2-4). The longest hairs on the third antennal segment is 2-3 times as long as the basal diameter of that segment (cf. Aphis fabae  which has longest hairs on the third antennal segment 0.6-2.4 times as long as the basal diameter of that segment). The middle and hind femora are mostly dark and tibiae are darkened on the apical quarter. The body length of Aphis evonymi adult is 1.7-2.9 mm.

 

Immature forms are a lighter reddish-brown and may have discrete pleural wax spots (see second picture above). From our observations the wax spots are much more prominent in alatiform immatures than in future apterous forms. Alate Aphis evonymi have a rather well developed series of transverse segmental bands on abdominal tergites as well as larger marginal and postsiphuncular sclerites (see picture above right, and below of an alate in alcohol).

The spindle aphid does not host alternate. It feeds on spindle (Euonymus europaeus). Apterous males and oviparae are produced in the autumn, and eggs are laid on the stems of spindle. Aphis evonymi occurs in several European countries.

 

Biology & Ecology:

Taxonomy

Jones (2006)  described Aphis evonymi, a brown aphid found on Euonymus europaeus (see picture below), under the name Aphis (Doralis) cognatella. Transference experiments (carried out under somewhat artificial conditions) showed that, although the aphid is normally found on Euonymus sp., it can exist for some time on some other plants, such as Rumex and Beta vulgaris which are also host plants of Aphis fabae. However, it does not colonise Vicia faba (bean). Following various taxonomic revisions, it was renamed to the earlier Aphis euonymi or, more correctly, Aphis evonymi. We have followed the line of Blackman & Eastop (2006)  and Heie (1980-1995)  (as Aphis euonymi) who both treat Aphis evonymi as a 'good' species, rather than a subspecies of Aphis fabae. Jorg (1995)  also accords Aphis evonymi full species status on the basis of electrophoretic analyses and morphological data.

The alternate case, for treating Aphis evonymi as a subspecies of Aphis fabae, is put by Muller & Steiner (1986)  based on the high level of morphological conformity and hybridization capability with other members of the Aphis fabae complex. The gynoparae in pure lineages are apterous. For the most part the aphid is restricted to Euonymus europaea as its host, but it does sometimes colonize other plants such as Valeriana officinalis. Distinguishing morphological characters from other Aphis fabae subspecies are the higher number (4 or 5) hairs on the VIIIth abdominal tergite, and the stronger and more numerous spinules on the abdominal marginal sclerites.

A similar case was made by HuiHong et al. (2010)  who divided Aphis fabae into 6 subspecies, i. e. Aphis fabae fabae, Aphis fabae cirsiiacanthoidis, Aphis fabae evonymi, Aphis fabae mordvilkoi, Aphis fabae solanella and Aphis fabae eryngii. These subspecies were differentiated based on the morphological characters and genetic differences of 34 samples based on four established subspecies and two proposed (=nominate) subspecies: Aphis fabae evonymi and Aphis fabae eryngii. Discriminant analysis demonstrated that the morphology of Aphis fabae mordvilkoi and the proposed subspecies significantly overlap. The individuals of Aphis fabae cirsiiacanthoidis and Aphis fabae solanella were significantly different from the nominate subspecies.

 

Life cycle
Aphis evonymi lives throughout the year on spindle (Euonymus europaeus) and other Euonymus species. Although artificial transferences have been made to some of the hosts of the Aphis fabae complex, there is no evidence of heteroecy occurring in nature.

 

Aphis evonymi may live in rather tight leaf rolls such as those above. Or they may spread out along the twigs as shown below.

The aphids above all appear to be fourth instar alatiform nymphs, but appearances can be deceptive. We have found brachypterous females with undeveloped wings which are producing offspring (see picture below).

Dixon (1972)  found that morphs of Drepanosiphum dixoni with reduced wings are more fecund than those with fully developed wings. Such forms may arise when nutritional or climatic conditions change markedly during the development of the aphid, so that priorities change from emigration to another host plant to increased reproduction on the current host plant. Such polyphenisms are an important source of aphids' ability to adapt to changing environments and exploit available resources.

 

Colour

The fruits of the hostplant, European spindle, are a vivid pink, which split to reveal bright orange seeds (see picture below). This is presumably warning coloration since the spindle tree has a number of poisonous components which, judging by their effects, are glycosides. The poisonous compounds are present throughout the plant, and consumption of the berries or leaves by man or domestic animals can induce diarrhoea, vomiting and loss of consciousness.

Euonymus europaeus fruit & seeds By Hectonichus  - Own work, CC BY-SA 3.0, Wikimedia. 

Some herbivores that feed on spindle display aposematic coloration, presumably to warn they sequester the spindle toxins. One such insect is the leaf notcher caterpillar (Pryeria sinica) which has striking black and white lines along its back (see Pryeria sinica ). Aphis evonymi is also aposematically coloured, being a rich red-brown (see picture below) with or without white bars, shown in several of the pictures above. Aphis evonymi colonies certainly contrast sharply with the young green leaves of spindle.

 

Natural enemies

There are surprisingly few natural enemies recorded in the literature for this species/subspecies, possibly because of the confused nature of the nomenclature for this aphid. Lysiphlebus fabarum is recorded from Aphis evonymi by Samin et al. (2014) , but with the aphid host feeding on burdock (Arctium lappa). There may therefore be an identification problem here.

We have encountered a variety of different predators and pathogens. The commonest coccinellid has been the harlequin ladybird (Harmonia axyridis).

Syrphid larvae (see picture below) also take a heavy toll of Aphis evonymi.

And, of course, midge larvae Aphidoletes aphidimyza (see picture below) are nearly always present.

Aphidoletes was much underrated in the past, but with the advent of commercialized biological control for the gardener, it is now recognised as one of the most effective aphid predators to release for biological control.

 

An Aphidius species also attacks Aphis evonymi producing the orange aphid mummies show above. Aphis evonymi is also attacked by various pathogens.

 

The red cadaver in the first picture above is almost certainly caused by an entomophthoran fungus. The black cadavers may be an Entomophthora species or they may be parasitized mummies.

 

Other aphids on same host:

Blackman & Eastop list 7 species of aphid  as feeding on spindle (Euonymus europaeus) worldwide, and provide formal identification keys. Baker (2015)  lists all 7 as occurring in Britain: Aphis aurantii,  Aphis evonymi, Aphis fabae cirsiiacanthoidis  Aphis fabae fabae  Aphis fabae solanella , Macrosiphum euphorbiae  and Myzus persicae. 

The picture above appears to show a mixed colony of Aphis evonymi (brown and white) and Aphis fabae (subspecies indet.) (black and white). The colonies of each species probably started on two separate leaves, but then moved to the twig as they matured. Most are alatiform fourth instar nymphs, and will migrate to other spindle bushes (Aphis evonymi) or to secondary hosts (Aphis fabae).

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).

Useful weblinks 

References

  •  Dixon, A.F.G. (1972). Fecundity of brachypterous and macropterous alatae in Drepanosiphum dixoni (Callaphididae, Aphididae). Entomologia Experimentalis et Applicata 15(3), 335-340. Abstract 

  •  HuiHong, Z. et al (2010). Subspecies differentiation of Aphis fabae Scopoli (Hemiptera, Aphididae) based on morphological and molecular data. Acta Zootaxonomica Sinica35(3), 537-545. Google Scholar 

  •  Jones, M.G. (1943). A brown Aphis, Aphis (Doralis) cognatella, sp. n., found on Spindle Tree. Bulletin of Entomological Research 34(3), 213-224. Abstract 

  •  Jörg, E. (1995). Studies on the Aphis fabae group (Homoptera, Aphididae). Inaugural Dissertation. Freiburg.  Full text 

  •  Muller, F.P. & Steiner, H. (1986). Beitrag zur vergleichenden Morphologie und Bionomie von Aphis euonymi. Deutsche Entomologische Zeitschrift 33(3), 257-267. Abstract 

  •  Samin, N. et al. (2014). A study on the Braconidae (Hymenoptera: Ichneumonoidea) from West Azerbaijan province, Northwestern Iran. Linzer biol. Beitr. 46(2), 1447-1448. Full text