Neuroterus numismalis is a gall wasp

Gall wasp

Gall wasps , also called Gallflies, are a family of the order Hymenoptera and are classified with the Apocrita suborder of wasps in the superfamily Cynipoidea...

 that forms chemically induced leaf gall

Gall

Galls or cecidia are outgrowths on the surface of lifeforms caused by invasion by other lifeforms, such as parasites or bacterial infection. Plant galls are abnormal outgrowths of plant tissues and can be caused by various parasites, from fungi and bacteria, to insects and mites...

s on oak trees. It has both bisexual and agamic (parthenogenetic) generations and forms two distinct galls on oak leaves, the Silk button gall and Blister gall. The galls can be very numerous with more than a thousand per leaf..

Synonyms

Neuroterus reaumuri, N. vesicator, Spathegaster vesicatrix, Cynips numismalis, and C. quercus-tiarae are previous binomials found in the literature.

Galls

This Silk button spangle gall has a cover of golden hairs that give the impression of silk thread. The 0.3 cm button-shaped galls have a pronounced concavity and sit tightly against the leaf lamina.
Blister galls are about 0.3 cm in diameter and green or greyish in colour; well camouflaged with the leaf lamina. The gall has narrow ridges running downwards on all sides from a central papilla on the upper surface and sometimes on the lower surface as well. Both galls are both unilocular and unilarval.

Gall wasp

The female wasp of the bisexual generation is about 1.8–2.4 mm in length; largely brown in colour with clear wings and hairy legs. The male is also winged and slightly shorter than the female.

The agamic generation consists of only female wasps which measure approximately 2.5 mm in length. The pointed head is black, with pale brown eyes and long clear wings are present with dark brown veins and hairs.

Agamic generation

In late summer the agamic generation develops in the circular, golden brown, raised, and disc-shaped structure, known as a 'Silk button spangle gall'. The gall increase in size even after they fall to the ground in autumn, this being achieved by cell enlargement rather than though further cell division. The gall wasp that causes the agamic generation was previously named as N. vesicator until the two generational status of the species was understood.

Bisexual generation

After having overwintered on the ground the females emerge from the Silk button gall in early spring and the lay their parthenogenetic (unfertilised) eggs in expanding oak leaf buds, forming the so called 'Blister Gall.' This second N. numismalis gall is located on the leaf blade as a structure which forms a convexity protruding from both the upper and lower lamina

The Blister galls produce the males and females of the bisexual generation in mid-summer and the fertilised eggs result in the Silk button gall generation.

Inquilines and parasites

The spangle gall generation in particular is effected by inquiline

Inquiline

In zoology, an inquiline is an animal that lives commensally in the nest, burrow, or dwelling place of an animal of another species. For example, some organisms such as insects may live in the homes of gophers and feed on debris, fungi, roots, etc...

s and parasites. Synergus albipes is an inquiline on the blister gall, whilst common hyperparasite

Hyperparasite

A hyperparasite is a parasite whose host is a parasite. This form of parasitism is especially common among entomophagous parasites....

s include Aulogymnus arsames, Aprostocetus aethiops, Eurytoma brunniventris, Mesopolobus fasciiventris, M. fuscipes, M. sericeus, M. tibialis and Torymus flavipes.

Silk button galls also have Synergus albipes as an inquiline and examples of hyperparasites include; Aulogymnus gallarum, Mesopolobus fasciventris, M. tibialis, Pediobius lysis and Torymus flavipes.

See also

• Knopper gall
  Knopper gall
  Andricus quercuscalicis is a gall wasp species inducing Knopper galls.Knopper galls develop as a chemically induced distortion of growing acorns on Pedunculate Oak trees, caused by gall wasps, which lay eggs in buds with their ovipositor...
  
  
• Oak marble gall
  Oak marble gall
  Oak marble galls develop as a chemically induced distortion of leaf buds on pedunculate oak , or sessile oak trees, caused by the parthenogenetic gall wasp which lays eggs within leaf buds using their ovipositor...
  
  
• Neuroterus quercusbaccarum
  Neuroterus quercusbaccarum
  The common spangle gall on the underside of leaves and the currant gall on the male catkins or occasionally the leaves, develop as chemically induced distortions on pedunculate oak , or sessile oak trees, caused by the cynipid wasp Neuroterus quercusbaccarum which has both agamic and bisexual...
  
  
• Neuroterus albipes
  Neuroterus albipes
  Neuroterus albipes is a gall wasp that forms chemically induced leaf galls on oak trees which has both bisexual and agamic generations and therefore forms two distinct galls, the smooth spangle gall and Schenck's gall...
  
  
• Neuroterus anthracinus
  Neuroterus anthracinus
  Neuroterus anthracinus is a widely distributed gall wasp that forms chemically induced leaf galls on oak trees. N. anthracinus has both bisexual and agamic generations and in consequence forms two distinct galls, the oyster gall and April-bud gall. -Synonyms:Ameristus Förster 1869, Diplobius Kinsey...
  
  

External links

• Silk Button Spangle gall

Sources

• Darlington, Arnold (1975) The Pocket Encyclopaedia of Plant Galls in Colour. Pub. Blandford Press. Poole. ISBN 0-7137-0748-8.
• Stubbs, F. B. Edit. (1986) Provisional Keys to British Plant Galls. Pub. Brit Plant Gall Soc. ISBN 0-9511582-0-1.