Pemphigus vesicarius

Life cycle, Identification & Distribution

In spring the fundatrices of Pemphigus vesicarius induce galls on their primary host, black poplar (Populus nigra). The gall (see first picture below) originates on a leaf upper-side from the base of its mid-rib. The gall develops in April-May into an irregular pale green structure with numerous tubular outgrowths, that covers the whole leaf. The fundatrix (see second picture below), which lives and feeds inside the gall, is dark slate-grey to blue-black and covered with wax.

Images above copyright Dr László Érsek, all rights reserved.

The mature fundatrix produces large numbers of offspring which develop within the gall and feed on the gall wall (see first picture below). By their fourth instar the developing wings of the offspring are visible (see second picture below), and by May most have matured to alatae.

Images above copyright Dr László Érsek, all rights reserved.

The adult Pemphigus vesicarius alate (not pictured) can be distinguished from Pemphigus populi alatae by the following characters: The first tarsal segments usually have 3-4 hairs on at least some tarsi (cf. Pemphigus populi, which almost always has 2 hairs on the first tarsal segments). Secondary rhinaria are elongate oval, and extend less than half way around the antenna. They have 6-11 secondary rhinaria on antennal segment III, 1-4 on segment IV, and 0-2 on segment V (cf. Pemphigus populi, which has 3-9 secondary rhinaria on antennal segment, 1-3 on segment IV, and 0-2 on segment V). Siphuncular pores are absent. The body length of a Pemphigus vesicarius alate is 1.7-3.0 mm.

Images above copyright Dr László Érsek, all rights reserved.

Alatae leave the gall in May-June through secondary holes at the apices of outgrowths (see picture above) and migrate to found colonies on the stems and basal parts of Colutea arborescens (bladder senna. The apterae on Colutea secrete abundant wax and have a body length of 2.7-3.0 mm. Pemphigus vesicarius is found in southern Europe, Algeria, south-west and central Asia, east to Pakistan and India.

Note: 'Bladder senna' should not be confused with 'senna pods', which have laxative properties and are the fruit of Egyptian senna (Senna alexandrina).

Other aphids on the same host

Primary hosts

Pemphigus vesicarius has been recorded from 4 Populus species (Populus gracilis, Populus nigra, Populus suaveolens, Populus tajikstanica).

• Blackman & Eastop list 41 species of aphid as feeding on black, or Lombardy poplar (Populus nigra, including var. italica) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 17 as occurring in Britain (Show British list).

Secondary hosts

Pemphigus vesicarius has been recorded from 1 Colutea species (Colutea arborescens).

• Blackman & Eastop list 7 species of aphid as feeding on bladder senna (Colutea arborescens) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 5 as occurring in Britain (Show British list).

Acknowledgements We especially thank Dr László Érsek for the images shown above. 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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