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Aphids on elm

Blackman & Eastop list about 75 species of aphids  as feeding on elms worldwide, and provides formal identification keys for aphids on Ulmus. Most of the aphids are in five genera: Colopha, Tinocallis,  Eriosoma,  Kaltenbachiella, and Tetroneura. 

The species below are those we have found most frequently, listed in rough order of abundance. Assistance on distinguishing English elm from Wych elm is given below. 

 

Tinocallis nevskyi (Pale Japanese elm aphid)

Adult alates of Tinocallis nevskyi are pale yellow, with pale or dusky antennae and legs (see pictures below). In autumn Tinocallis nevskyi have pigmentation on the head, thorax and and siphunculi and frequently also on the tips of their marginal tubercles.

 

The various body processes of Tinocallis nevskyi can be seen by careful examination of the pictures showing the winged adults, above and below (left). The pronotum has two pairs of pale finger-like spinal processes. The mesonotum has one pair of large conical processes. The abdomen has spinal processes on tergites 1 and 2, and lower wart-like tubercles on the other tergites and marginal tubercles. Their antennae are 0.76-0.96 times the body length. The wings are hyaline and the forewing veins are not bordered with fuscous. Tinocallis nevskyi siphunculi are short. The body length is 1.4-2.1 mm.

The pale Japanese elm aphid feeds on elm (Ulmus. This species originated in central and south-west Asia, but has spread over much of Europe. In some European countries Tinocallis nevskyi is now among the most common aphid species.

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Tinocallis takachihoensis (Japanese elm aphid)

The winged viviparae of Tinocallis takachihoensis (see first picture below) are pale yellow-green with a shiny black head and thorax. There are black markings on the wings, and a black patch where the hind femur meets the hind tibia. The body length of Tinocallis takachihoensis alates is 1.8-2.0 mm. The immatures (see second picture below) are pale yellow green with numerous tubercles topped with capitate hairs.

 

The pattern of black markings on Tinocallis takachihoensis wings (see first picture above) is diagnostic. The pronotum has two pairs of paired dorsal processes which also be seen above. The posterior pair is large and dark whilst the anterior pair is small and pale. There are also two pairs of pale paired dorsal processes on the abdominal dorsum. The head bears no dorsal processes (this distinguishes Tinocallis takachihoensis from Tinocallis ulmiparvifoliae), and there are no brown markings on the abdominal dorsum (which distinguishes Tinocallis takachihoensis from Tinocallis platani).

The Japanese elm aphid feeds on elm (Ulmus spp) and some other genera in Japan, China and eastern Siberia. Tinocallis takachihoensis has also been introduced to Europe (France, Germany, England, Netherlands, Sicily, Andorra) and the USA. It now appears be established in most of these countries.

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Eriosoma ulmi (Elm-currant aphid)

In spring Eriosoma ulmi fundatrices develop in yellowish or whitish green galls on elm (see first picture below). The fundatrices and their apterous offspring are dark green and wax-covered. The six segmented antennae are 0.18-0.2 times the length of the body, with a terminal process that is a quarter of the length of the base of the last antennal segment. There are no siphunculi or siphuncular pores. Their alatiform offspring are brownish or dull green (cf. Eriosoma grossulariae which has light green immature alatae). The adult winged viviparae of Eriosoma ulmi are dark green to bluish grey with dark cross bands on the abdomen (see second picture below). The antennae are about half the length of the body. The siphuncular pores are large and sited on low dark hairy cones.

 

The lack of secondary rhinaria on the fifth antennal segment is diagnostic (cf. Eriosoma crataegi & Eriosoma lanigerum which have 4-8 secondary rhinaria on the fifth antennal segment). Also the antennal terminal process is short and thick (cf. Eriosoma grossulariae which has the terminal process longer and thinner).

The elm-currant aphid host alternates from the primary host elm (Ulmus spp.) to the secondary host, the roots of currant (Ribes). Eriosoma ulmi is found in Europe and much of Asia, eastward to Mongolia and China. It has recently been introduced into Canada.

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Tetraneura ulmi (Elm-grass root aphid)

On the primary host, elm, Tetraneura ulmi develop within galls on the leaves. The galls are stalked, approximately bean-shaped, smooth and shiny, and coloured reddish-green and/or yellow (see first picture below). The fundatrix, which stimulates production of the gall, is light green with the head, thorax, antennae and legs dark and transverse bands of light wax across the abdomen and thorax (see second picture below).

 

The offspring of the Tetraneura ulmi fundatrix develop within the gall to winged viviparous alates. The adult alates (not pictured here) have a shiny black head, thorax, antennae and legs, and greyish black abdominal segments. The body length of Tetraneura ulmi alates is 1.8-2.6 mm.

The adult apterae on the secondary host, grass roots, are readily identified, being pale orange yellow, yellowish white or reddish (see picture above). The head, prothorax and appendages are brown, and the body is (sometimes) lightly dusted with wax.

Tetraneura ulmi host alternates. The winged forms of the elm-grass root aphid emerge from elm galls (Ulmus spp.) in June-July to colonize roots of grasses (Poaceae). Populations without sexual forms occur commonly on secondary hosts. In September winged forms make a return migration to elm where they produce larvae which feed on the bark, and mature to apterous males and females. Fertilized females only lay one egg each. Tetraneura ulmi is found in Europe, across Asia to eastern Siberia, and has been introduced to North America.

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Species of elm

We cover two species of elm, English elm (Ulmus procera) and wych elm (Ulmus glabra). The leaves of English elm (see first picture below) are dark green and almost circular. They do not have the pronounced acuminate tip at the apex which is typical of the genus. The tree does not produce fertile seed as it is female-sterile, so regeneration is entirely by root suckers. Although it can grow to a large tree, it is nowadays mainly found as a shrub as older plants die from Dutch Elm disease.

 

The leaves of wych elm are obovate (teardrop shaped) with an asymetric base and tapering to a long point at the tip (acuminate). They often have three or more lobes near the apex. Reproduction is by seed. The wych elm is also highly susceptible to Dutch elm disease, but is less favoured than English elm by the beetle vectors of the fungus.

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

  •  Blackman, R.L. & Eastop, V.F. Aphids on the world's plants An online identification and information guide. Full text