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Pemphigus gairi and Pemphigus phenax

Poplar pouch gall aphids

On this page: Identification & Distribution  Other aphids on the same host 

Identification & Distribution:

In spring Pemphigus gairi and Pemphigus phenax form yellowish or reddish pouch-shaped gallson or near the midrib (see pictures below), and usually more or less in the middle of a leaf of poplar, mainly black poplar (Populus nigra). The slit-like opening on the underside extends over the entire length of the gall. (cf. Pemphigus populinigrae  which induce broader pouch-shaped galls only partly-opening on the underside of the lamina).

  • Galls of Pemphigus gairi are rather thin walled, slightly shining, green-yellow in colour and only rarely slightly reddish. The swelling is nowhere more than four times the normal thickness.
  • Galls of Pemphigus phenax have a slightly wrinkled surface, more or less red in colour and often with yellow sides. The swelling is over five times the normal thickness .
Given the features above (colour and thickness) all the galls below would appear to be Pemphigus phenax.
But note that some authorities (e.g. Blackman ) suggest that the galls are too similar to differentiate and, to distinguish between Pemphigus gairi and Pemphigus phenax, emigrant alatae should be examined.

Inside the gall the developing Pemphigus fundatrix is covered with wax (first picture below). We removed the wax from the one in the second picture below to show distinguishing features. The fundatrix is green or greyish green and has no siphunculi. The 4-segmented antennae are about 0.12-0.15 times the body length.

Winged viviparae (see below) emerge from these galls in summer through an opening on the underside of the leaf. They have a black head and pterothorax, small siphunculi and a rather elongate greenish wax-dusted abdomen.

  • For Pemphigus gairi the axial length (= distance between two most distant points) of the primary rhinarium is less than 35 µm. The third antennal segment has 7-12 secondary rhinaria, the fourth has 3-6, the fifth has 1-4 and the sixth has 1-7.
  • For Pemphigus phenax the primary rhinarium on the fifth antennal segment is usually much enlarged, its axial length 35 µm or more with small islands. The third antennal segment has 6-12 secondary rhinaria, the fourth has 2-3, the fifth has 0-3 and the sixth has 2-5.

Pemphigus gairi host alternates between poplar and fool's parsley (Aethusa cynapium). In summer they live above ground on the secondary host, often in the inflorescences (flower-heads). Pemphigus gairi has been found in England, Czech Republic and Ukraine, but it probably occurs widely in Europe.

Pemphigus phenax host alternates between poplar and the roots of wild and cultivated carrots (Daucus carota). Apterae on carrot roots are pale lemon-yellow to yellowish white with white wax. Colonies may also persist parthenogenetically on carrots that remain in the ground through the winter. Pemphigus phenax is found in northern Europe (England, Denmark, France, Germany, Netherlands, Sweden), and is also recorded from Turkey and west Siberia.

 

Other aphids on same host:

Blackman & Eastop list 40 species of aphid  as feeding on Black, or Lombardy poplar (Populus nigra) worldwide, and provide formal identification keys.

Of those aphid species, Baker (2015)  lists 17 as occurring in Britain: Aulacorthum solani,  Chaitophorus leucomelas,  Chaitophorus populeti,  Chaitophorus populialbae,  Pemphigus bursarius,  Pemphigus gairi, Pemphigus phenax, Pemphigus populi, Pemphigus populinigrae, Pemphigus protospirae,  Phloeomyzus passerinii, Pterocomma populeum,  Pterocomma tremulae,  Stomaphis longirostris, Thecabius affinis,  Thecabius lysimachiae, and Tuberolachnus salignus. 

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. et al. (in preparation). Aphids (Anoeciinae, Lachninae, Eriosomatinae, Phloeomyzinae, Thelaxinae, Hormaphidinae, Mindarinae). 2(8) Handbooks for the identification of British insects. Royal Entomological Society, London