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Pemphigus populi

Club-shaped poplar-gall aphid

On this page: Identification & Distribution Biology & Ecology Damage & Control Other aphids on the same host

Identification & Distribution:

In spring Pemphigus populi form green or greenish-yellow globular outgrowths of the mid-rib of the leaves of black poplar (Populus nigra) which are close to the base of the leaf (see first picture below) (cf. Pemphigus gairi & Pemphigus phenax which form yellowish or reddish elongate pouch-shaped galls which are more or less in the middle of a leaf). The outgrowths become club-shaped with the basal part narrower than the apex when mature.

Mature Pemphigus populi alatae (see first picture above) are greyish green with abundant wax. They have small but distinct marginal wax gland plates. The terminal process of the antenna (see second picture above) is 0.25-0.4 times as long as the basal part of the sixth antennal segment. They have 3-9 secondary rhinaria on the third antennal segment, 1-3 rhinaria on the fourth segment and 0-2 on the fifth segment. The sixth antennal segment is always without secondary rhinaria (cf. Pemphigus populinigrae, and Pemphigus gairi & Pemphigus phenax which all have some secondary rhinaria on the sixth antennal segment.) The apical segment of the rostrum is about 0.5-0.7 times as long as the second segment of the hind tarsus. Siphuncular pores are absent (cf. Pemphigus populinigrae, Pemphigus bursarius, Pemphigus gairi & Pemphigus phenax which all have siphuncular pores). The body is 1.5-2.4 mm long.

Pemphigus populi host alternates from various poplar species, mainly black poplar (Populus nigra) and lombardy poplar (Populus nigra 'italica'), to the roots of various species of Fabaceae, especially meadow vetchling (Lathyrus pratensis), black medic (Medicago lupulina) and tall melilot (Melilotus altissimus).

 

Biology & Ecology:

Life cycle

Pemphigus populi fundatrices hatch from fertilised overwintering eggs in late April, and induce development of the characteristic club-shaped gall (see pictures below of gall and developing fundatrix found in Britain).

Image copyright Dr László Érsek, all rights reserved.

The gall is induced by the feeding of the fundatrix inside the gall (see second picture above). The fundatrix has abdominal wax gland plates which secrete whitish wax over the body.

Second image copyright Dr László Érsek, all rights reserved.

Both images copyright Dr László Érsek, all rights reserved.

The fundatrix produces pale greenish yellow offspring (see picture above) which all develop to alatae within the gall.

The fundatrix produces large numbers of wax-covered greyish green alatae (see image below). Pemphigus aphids have developed an efficient way of handling their excreted honeydew. They use a very hydrophobic (=water-repellant) wax that coats every element inside the gall: the gall itself, the aphids and the liquid honeydew. The secreted powdery wax has three distinct roles: (i) it is hydrophobic; (ii) it creates a microscopically rough inner gall surface made of weakly compacted wax needles, making the gall ultra-hydrophobic; and (iii) it coats the honeydew droplets, converting them into liquid marbles (see picture below of two such 'marbles'), that can be rapidly and efficiently moved. This produces a virtually non-stick environment, which is of vital importance in this enclosed space (Pike, 2002).

Image copyright Dr László Érsek, all rights reserved.

Pike (2007) made a fascinating comparative study of the ecology of three gall-dwelling species: Pemphigus populi, Pemphigus spyrothecae, and Pemphigus bursarius. The three species have clear differences in their levels of social behaviour: Pemphigus populi is highly asocial. It has no soldiers, has the shortest galling phase, and exhibits synchronised development of a small number of individuals in a sparsely populated gall. Pemphigus spyrothecae on the other hand is a highly social species with aggressive morphologically-specialised soldiers, the longest galling phase, and unsynchronised development of a large number of individuals in a densely-populated gall. Pemphigus busarius is intermediate in these various characteristics and behaviours.

Pike (2007) noted that the opening of the galls of Pemphigus populi is highly unusual. Wide fissures open in the gall starting at its apex and often extend such that the gall's inner surface is turned entirely outward (see picture below).

Image copyright Dr László Érsek, all rights reserved.

The offspring of the fundatrix are almost entirely alate, and these all emerge immediately the galls open.

Immediately following emigration from the gall of the alatae, Pike found 42.0% of galls contained predators, 47.3% contained inquiline aphids, and 22.7% contained aphidopathogenic fungus. Hence 87.3% of the 150 monitored galls were affected by competitors and natural enemies that would have been fatal to these aphids, had they continued to inhabit their galls.

El-Akkad & Zalat (2000) described an infestation of Pemphigus populi on Lombardy poplar in Sinai, Egypt. Ecott (2003) found galls of Pemphigus populi not uncommonly on black poplar at Hainault Forest, Essex. Some of the galls were broken open, apparently by predators. Osiadacz & Halaj (2014) report Pemphigus populi for the first time from Poland. They concluded that this most likely reflects a rapid, almost invasive, increase in range of this species.

 

Other aphids on same host:

Primary hosts

Pemphigus populi has been recorded from at least 7 Populus species (Populus balsamifera, Populus ×canadensis, Populus gracilis, Populus nigra, Populus pilosa, Populus tajikistanica, Populus talassica).

Secondary hosts

Acknowledgements

We especially thank Dr László Érsek for some of the images shown above, and Plumpton College for their kind assistance, and permission to sample.

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).

Useful weblinks

References

  • Ecott, B.A. et al. (2003). Pemphigus populi (Hemiptera: Aphidiidae) in Hainault Forest, Essex. Cecidology 18(2): 56 Full text

  • El-Akkad, S. & Zalat, S. (2000). Populus galls induced by Pemphigus aphids in Sinai. Egyptian Journal of Biology 2, 15-19. Full text

  • Osiadacz, B. & Halaj, R. (2014). First records of gall-inducing aphid Pemphigus populi (Hemiptera: Aphidoidea, Eriosomatidae) in Poland with gall-based key to Central and North European species of the genus. Entomologica Fennica 25, 16-26. Full text

  • Pike, N. et al. (2002). How aphids loose their marbles. Proceedings of the Royal Society of London B 269(4), 1211-1215. Full text

  • Pike, N. et al. (2007). Ecological correlates of sociality in Pemphigus aphids, with a partial phylogeny of the genus. BMC Evolutionary Biology, 7: 185. Full text