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Giant oak aphidIdentification & Distribution Biology & Ecology Other aphids on the same host Damage & Control
Identification & Distribution:Adult apterae of Stomaphis quercus are elongate oval shining dark brown. They have numerous densely placed, thin, erect hairs on the body, antennae and legs. The antennae are dark, about 0.4 times the length of the body, with antennal segment 3 paler than the others. The rostrum is exceptionally long, in the adult nearly twice as long as the body. It is proportionally even longer in immatures. There are dark spinal spots on abdominal tergites I-VI and cross bars interrupted in the middle on tergites VII and VIII. The body length of Stomaphis quercus apterae is 5.3-7.0 mm.
Image copyright Bernhard Seifert, all rights reserved.
Given its size, the alate has rather small wings. The wing veins have brown borders.
Stomaphis quercus is found on several species of oak (Quercus), and sometimes also on birch (Betula). It is always ant attended, normally by Lasius fuliginosus (see picture above), but sometimes by Lasius brunneus. Sexual forms occur in September-November. The species is rare in UK and may be locally extinct. Its stronghold was Breckland, East Anglia which is now largely under agriculture. Stomaphis quercus is found throughout Europe and in west Siberia.
Biology & Ecology:
Goidanich (1958) made a detailed study of the life cycle and attendance of Stomaphis quercus by Lasius fuliginosus on oak, and Lorenz & Scheurer (1998) looked at populations on birch. Until recently some authorities considered there to be two species of the genus Stomaphis, feeding on oak and birch respectively. Depa et al. (2012) used mitochondrial DNA to determine whether these two populations differ. They found no significant differences between birch-feeding and oak-feeding populations, and concluded they were the same species. However, they did find morphologically and ecologically distinct populations of Stomaphis feeding on oak. This led to the recognition of a new species, Stomaphis wojciechowskii, which in life differs from Stomaphis quercus in being pale in colour, slightly powdered in wax, and with an obvious row of darker spinal plates.
Loi et al. (2012) gave some fascinating details on the interactions between Lasius brunneus and Stomaphis quercus in Sardinia. They found Stomaphis quercus undergoes its cycle almost exclusively inside the nest of the tending ant. Most aphid feeding activity takes place inside chambers purposely excavated in the cork of the stem and main branches by the ant workers. Often these chambers contain groups of 8-12 aphids feeding next to each other. Only in the months of April and May did Loi et al. find individuals feeding in the crevices of the cork bark. When these aphids were disturbed, the attendant ant workers quickly pulled the aphids by their body cuticle so that they extracted their stylet from the plant tissues as rapidly as possible. Once the stylet was free, the ants urged the aphids to move away quickly, pulling them by the legs or, if young nymphs, the ants used their mandible to snatch the aphid's rostrum and haul them into shelter.
Only one winged viviparous female Stomaphis quercus was observed in each nest, suggesting to Loi et al. that the care given by the ants limits or sometimes inhibits the formation of alates. This may extend to the cutting off their wings, as is known to be practised by ants of the genus Lasius. Loi et al. suggest that the shortage of alates might explain the limited possibility of dispersion of this aphid, which thus remains within the territory of the ants. In a study on ants and habitat specificity, Hopkins & Thacker (1999) showed that Stomaphis quercus only occupied trees within 17 meters of a Lasius fuliginosus nest.
In much of Europe Stomaphis quercus is a prime candidate for conservation (see rare aphids and conservation ). This is partly because of its close association with ants, which are often keystone species in woodland. But also because it is undoubtedly rare in Britain - its former stronghold was in Breckland, now largely under agriculture.
Other aphids on same host:
Damage and control:
In southern Europe the ant Lasius brunneus are serious pests of cork oak (Quercus suber) (see http://www.creaf/uab.es/xeg/brunneus/english/pest.htm ) hence, since it is sometimes present in Lasius brunneus nests, Stomaphis quercus may also be seen as a pest. Damage results from the construction of nest galleries by the ants. These degrade the cork and make extraction of cork difficult because of insufficient detachment of the bark. In Spain laboratory control tests using baits (with borax or chlorpyrifos) were effective, but field tests were not successful (Espadaler, 2006) ). Loi et al. (2012) recommended integrated ant-control, combining bark removal with the use of insecticide baits, in areas where control was necessary.