Eriosoma lanuginosum

Identification & Distribution:

In spring the Eriosoma lanuginosum fundatrix and her offspring develop in large, closed, bloated-leaf galls (see first picture below) on various elm (Ulmus) species. This gall is produced by extreme enlargement of the cells of the leaf parenchyma on one side of the mid-rib near its base. The gall tissue is light green at first and covered with fine white hairs, becoming brown as the gall matures. There are often clusters of galls near the ends of branches (see second picture below). The fundatrix of Eriosoma lanuginosum which initiates the gall is blackish and wax powdered (not pictured), but the offspring of that fundatrix (known as fundatrigeniae) are wax-powdered, wingless and yellowish when immature.

Alates produced in the second and third generations of Eriosoma lanuginosum on elm are dark green to black and wax powdered. The body length of the adult Eriosoma lanuginosum alate is 2.1-3.1 mm. Apterae on the secondary hosts are pale yellow to reddish, with an adult body length of 2.0-2.7 mm.

The alates leave the galls on elm in late June-July and migrate to found colonies on fibrous rootlets of pear (Pyrus communis) or quince (Cydonia). The return migration to elm bark occurs in September. Eriosoma lanuginosum occurs throughout Europe, the Mediterranean area, and Asia east to Pakistan.

Other aphids on same host:

Blackman & Eastop list about 75 species of aphids as feeding on elms worldwide, and provides formal identification keys for aphids on Ulmus.

• Blackman & Eastop list 22 species of aphids that feed on English elm (Ulmus procera) worldwide (Show World list). Of these, Baker (2015) lists 14 as occurring in Britain (Show British list).

• Blackman & Eastop list 22 species that feed on wych elm (Ulmus glabra) worldwide (Show World list). Of these, Baker (2015) lists 15 as occurring in Britain (Show British list).

Acknowledgements Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made 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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