Pachypappa tremulae

Identification & Distribution:

In springtime Pachypappa tremulae fundatrices (not shown here) may be found on the twigs of aspen (Populus tremula). They are unusually large (body length 5.0-6.6 mm) and are almost globular. They are a dirty reddish or yellowish brown colour, but appear silvery as they are covered with long fine hairs. They have no siphuncular pores and do not secrete any wax. The offspring of the fundatrix move on to the new shoots and form a rosette like leaf nest (see first picture below) formed by bending of the leaf petioles and stunting of growth of the shoot.

Guest images copyright Volker Fäßler, all rights reserved

These offspring all develop to winged individuals (see second picture above) which are orange or reddish brown, covered in wax and with very small siphuncular pores. They migrate in June to form colonies on the roots of spruce (Picea abies). Pachypappa tremulae apterae on spruce are pale yellowish white with tufts of wax posteriorly. Sexual forms then return to aspen in autumn. Pachypappa tremulae is widely distributed in the northern palaearctic, east to China and Japan.

Biology & Ecology:

Baker (2012) found leaf-nests containing Pachypappa tremulae on most aspen trees in June 2012 at Dundreggan in Scotland. We're pleased to be able to show the photos of Alan Watson Featherstone (2012) of Pachypappa tremulae at Dundreggan.

Guest image copyright Alan Watson Featherstone all rights reserved.

The offspring of the fundatrix suck the sap from one side of the leaf petiole. This causes each infested leaf to droop downwards, so forming a tent-like structure known as a leaf nest.

Guest image copyright Alan Watson Featherstone all rights reserved.

The developing aphids are orange-brown in colour and they are covered in wax.

Guest image copyright Alan Watson Featherstone all rights reserved.

One function of the wax coating of these aphids is defense against potential predators. The other major function is to coat the honeydew droplets (see picture above) so that they do not foul the aphid colony.

Guest image copyright Alan Watson Featherstone all rights reserved.

All the aphids in the leaf nest develop to alatae (see picture above).

Guest image copyright Alan Watson Featherstone all rights reserved.

These alatae are so thickly covered in wax that their underlying red-brown colouration is obscured and they appear dark grey.

The alatae migrate in June to form colonies on the thin mycorrhizal root ends of spruce.

Other aphids on same host:

Primary host

Pachypappa tremulae has been recorded from 5 Populus species (Populus ×berolinensis, Populus canescens, Populus davidiana, Populus suaveolens, Populus tremula).

Blackman & Eastop list 17 species of aphid as feeding on European aspen (Populus tremula) worldwide, and provide formal identification keys (Show World list).

Of those aphid species, Baker (2015) lists 11 as occurring in Britain (Show British list).

Secondary hosts

Pachypappa tremulae has been recorded from 3 spruce species: Norwegian spruce (Picea abies = Picea excelsa), oriental spruce or Caucasian spruce (Picea orientalis) and Colorado spruce (Picea pungens).

• Of the 28 species of aphids they list as feeding on Norwegian spruce (Picea abies) worldwide (Show World list), Baker (2015) lists 16 as occurring in Britain (Show British list).

• Of the 14 aphid species Blackman & Eastop list as feeding on Caucasian spruce (Picea orientalis) worldwide (Show World list) Baker (2015) lists 12 as occurring in Britain (Show British list).

• Of the 25 aphid species Blackman & Eastop list as feeding on Colorado Spruce (Picea pungens) worldwide (Show World list) Baker (2015) lists 13 as occurring in Britain (Show British list).

Damage and control

Shrimpton (1985) reported the presences of Pachypappa tremulae as a conifer pest in several nurseries in British Columbia and Alberta. The aphid was usually found on container spruce and spruce potted for grafting with few records from bare root. The white waxy infestations were on the surface of the plug between the roots and the container wall, closer to the top of the plug than the bottom. However, most nurseries with infestations of this root aphid did not report any chlorotic or undersized individuals, and it was anticipated that damage would be minimal if nutrients and moisture were adequate.

Acknowledgements Our especial thanks to Volker Fäßler for his images from Germany, and to Alan Watson Featherstone for his images from Dundreggan, Scotland. 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 Baker, E. (2012). Aphids and their parasitoids at the Dundreggan estate. Report. Dransfield, R.D. & Brightwell, R. (2013). Aphids and their natural enemies and mutualists at Dundreggan, Scotland. Report, InfluentialPoints.com. Full text Shrimpton, G. (1985). Four insect pests of conifer nurseries in British Columbia. USDA For. Serv. Gen. Tech. Rep. INT-185 Full text