Andricus lignicola

Cola-nut galls[1] develop as a chemically induced distortion of leaf axillary or terminal buds on pedunculate oak (Quercus robur) or sessile oak (Quercus petraea) trees, caused by the agamic gall wasp Andricus lignicola (Hartig, 1840) which lays single eggs within leaf buds using their ovipositor. A previous name or synonym for the species A. lignicola is A. lignicolus and A. venheurni.

Cola-nut gall
Mature galls on pedunculate oak
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Cynipidae
Genus: Andricus
Species:
A. lignicola
Binomial name
Andricus lignicola
(Hartig, 1840)

The physical appearance of the galls
Cola-nut gall cut open to show the unilocular cavity
Oak marble galls showing two stunted and two normal-sized examples

The galls are found in small groups, which however do not coalesce, helping to prevent mis-identification with the oak marble gall (Andricus kollari), in addition the shape is ovoid rather than spherical and it is scaly rather than smooth. It grows up to about 10 x 8 mm and is at first green, rapidly changing to grey-brown, with light red patches where the original bud scales have separated. It is hard and firm, but does not always persist on the tree for very long.[2] Once the imago has emerged a small circular hole is apparent.[1]

Distribution
Cola-nut gall showing exit hole

It is well known in continental Europe, occurring from Great Britain to Asia Minor.

Life-cycle

The imago of the agamic phase emerges in early summer following the gall's inception. The bisexual generation gall is very similar to that of A. kollari, effecting the live bud of Quercus species[2] and has only been seen under culture conditions (1975).[3] Removing and destroying cola-nut galls before they dry and the wasps emerge may help to reduce an infestation. While fairly large, and sometimes present in quite large numbers on scrub specimens, they cause no measurable harm.

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See also

References
  1. Darlington, Arnold (1975) The Pocket Encyclopaedia of Plant Galls in Colour. Pub. Blandford Press. Poole. ISBN 0-7137-0748-8. P. 155.
  2. Stubbs, F. B. Edit. (1986) Provisional Keys to British Plant Galls. Pub. Brit Plant Gall Soc. ISBN 0-9511582-0-1. P. 52.
  3. Darlington, Arnold (1975) The Pocket Encyclopaedia of Plant Galls in Colour. Pub. Blandford Press. Poole. ISBN 0-7137-0748-8. p. 155.
  • "Gall". Infoplease encyclopedia. Retrieved 4 November 2008.
  • "Andricus lignicola". Hedgerows, Hedges and Verges of Britain and Ireland (Hedgerowmobile). Archived from the original on 17 February 2012. Retrieved 18 December 2011.


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