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Identification & Distribution

Adult apterae of Phylloxera glabra (see picture below) are yellowish orange. The dorsal processes (=projections) are undeveloped, and the tergum (=thickened dorsal plate) is nearly smooth (cf. Pylloxera quercus sp. group, including Phylloxera coccinea, which have club-shaped dorsal processes on the thorax). The primary rhinarium on the third antennal segment is subapical (=below or near the apex) with the terminal process developed. Abdominal tergites 2-5 have spiracles.

First image above copyright Alan Outen, all rights reserved

The oak leaf phylloxera lives without host alternation on oak leaves (mainly Quercus robur). Female Phylloxera glabra tend to surround themselves in concentric circles of their eggs (see picture above). After hatching, their nymphs wander off leaving gaps in the circle. Or If disturbed, the adult female may leave.

Feeding causes necrotic spots on the leaves (see pictures above and below).

Severe infestations can lead to a general browning of the leaves and premature leaf fall, but growth will only be affected in young trees.

 

Biology & Ecology

Life cycle

The oak leaf phylloxera overwinters in the egg stage in crevices in the bark of oak trees. The eggs hatch in spring and the nymphs feed on the underside of leaves. Lubiarz (2001)  also found them overwintering as larvae in bark slits.

Once mature the adult apterae start to deposit eggs in a circle around them (see picture below). The first eggs are laid very close to the female.

Once that circle is complete, the aphid backs up on to a previously laid egg and starts depositing another circle of eggs around the first (see picture below).

Lubiarz (2001)  found the number of eggs per female Phylloxera (Phylloxera glabra and Phylloxera coccinea) varied from 2 to 121.

Natural enemies
Phylloxera glabra is regularly preyed upon by the larva of the neuropteran Conwentzia psociformis (Blackman & Eastop (1994) ). We found the neuropteran larva shown below feeding on Phylloxera glabra nymphs on an English oak leaf. It closely resembles other images of Conwentzia larvae.

We also found eggs that had been killed in situ (see picture below), although we cannot tell if these deaths resulted from predators or a fungal pathogen.

Steffan (1972) in Szentkiralyi (2001)  reported that Phylloxera glabra were predated by larvae of various lacewing species including Chrysotropia ciliata, Nineta flava, Dichochrysa prasina and Sympherobius pygmaeus.

 

Other aphids on same host:

Blackman & Eastop list about 225 species of aphids  as feeding on oaks worldwide, and provides formal identification keys for aphids on Quercus.

Of the 34 species on common or pedunculate oak (Quercus robur) Baker (2015)  lists 14 as occurring in Britain: Hoplocallis picta,  Lachnus longirostris,  Lachnus roboris,  Moritziella corticalis, Myzocallis boerneri,  Myzocallis castanicola,  Phylloxera glabra, Stomaphis quercus,  Thelaxes dryophila,  Thelaxes suberi,  Tuberculatus annulatus,  Tuberculatus borealis,  Tuberculatus neglectus  and Tuberculatus querceus.

Acknowledgements

Our thanks to Alan Outen of the Bedfordshire Invertebrate Group  for sending us photographs of Phylloxera glabra and samples thereof.

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

  •  Lubiarz, M. (2007). Life cycle and number dynamics of Phylloxera sp. on pedunculate oak (Quercus robur) in industrial and protected areas. Aphids and other Hemipterous Insects 13 , 137-144. Full text 

  •  Szentkiralyi, F. (2001). Lacewings in vegetables, forests, and other crops. In: McEwen, P.K. et al. (eds) Lacewings in the Crop Environment. Cambridge University Press.  Google Books