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Genus Eriosoma

Woolly aphids

Species Overview: Genus Eriosoma  Eriosoma lanigerum  Eriosoma ulmi 

Genus Eriosoma [Calaphidini]

Both winged and wingless aphids have rather conspicuous siphuncular pores with partially chitinized rims surrounded by a ring of hairs. Most species are wax-covered. The forewing of winged individuals usually has only one branch in the medial vein.

There are about 35 species most of which host alternate between galls on elm (ulmiceae) and secondary hosts such as apple (Rosaceae) and currants (Grossulariaceae). They typically have a sexual stage in the life cycle. They are not attended by ants.

 

Eriosoma lanigerum (Woolly apple aphid)

Wingless females on the secondary host are purple, red or brown and are are covered in thick white flocculent wax. This is produced by distinct wax glands on the head and along the thorax and abdomen. The six segmented antennae are 0.17-0.24 times the length of the body. The body length of apterae is 1.2-2.6 mm. Winged viviparous females (fourth instar alatiform nymphs shown in the picture below left) are reddish brown with very small wax glands and consequently much less wax. Their antennae are about 0.4 times the length of the body.

 

The wingless females live in dense colonies (see picture above right) on the roots, trunk or branches of the (secondary) host apple (Malus) and related species, often causing deformation and cancer-like swellings of bark. Sexual forms appear to have been lost, and overwintering is in fissures on the lower part of the trunk and on the roots. It is a pest of apple throughout the world.

 

Eriosoma ulmi (Elm-currant aphid)

Fundatrices in spring develop in yellowish or whitish green galls on elm (see first picture below). These are formed by downward curling, twisting and blistering of one edge of a leaf. 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 (see second picture below). The adult winged viviparae are dark green to bluish grey with dark cross bands on the abdomen. The antennae are about half the length of the body. The siphuncular pores are large and sited on low dark hairy cones.

 

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

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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