Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Oak leaf phylloxeraOn this page: Identification & Distribution Biology & Ecology Life cycle Natural enemies Other aphids on the same host
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
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 enemiesPhylloxera 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 15 as occurring in Britain: Hoplocallis picta, Lachnus longirostris, Lachnus roboris, Moritziella corticalis, Myzocallis boerneri, Myzocallis castanicola, Phylloxera glabra, Stomaphis quercus, Stomaphis wojciechowskii, Thelaxes dryophila, Thelaxes suberi, Tuberculatus annulatus, Tuberculatus borealis, Tuberculatus neglectus and Tuberculatus querceus.