Andricus foecundatrix (formerly ''Andricus fecundator'') is a parthenogenetic gall wasp which lays a single egg within a leaf bud, using its

ovipositor The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...

, to produce a

gall Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...

known as an oak artichoke gall, oak hop gall, larch-cone gall or hop strobileA Nature Observer's Scrapbook
/ref> The gall develops as a chemically induced distortion of leaf axillary or terminal buds on pedunculate oak (''Quercus robur'') or sessile oak (''Quercus petraea'') trees. The larva lives inside a smaller hard casing inside the artichoke and this is released in autumn. The asexual wasp emerges in spring and lays her eggs in the oak catkins. These develop into small oval galls which produce the sexual generation of wasps.Galls on UK Safari
/ref>The Virtual Filed Guide UK
A yew artichoke gall caused by the fly '' Taxomyia taxi'' also exists, but is unrelated to the oak-borne species. Previous names or synonyms for the species ''A. fecundator'' are ''A. fecundatrix'', ''A. pilosus'', ''A. foecundatrix'' (see below), ''A. gemmarum'', ''A. gemmae'', ''A. gemmaequercus'', ''A. gemmaecinaraeformis'' and ''A. quercusgemmae''. The scientific name is now once again ''Andricus foecundatrix''.

Galls

Young galls exhibit a tuft of long hairs protruding from the centre of the 'artichoke', the remainder being overlapping scales. The hairs are attached to the more solid gall which is released and drops to the ground from August onwards. After August the 'gall' is still visible, but it is really just the distorted leaf bud after the gall has fallen. A well grown specimen can be 2.0 cm long, dark green or russet, generally developing in June and reaching its full size before autumn. The hairy catkin galls are oval, pointed, unilocular and unilarval structures, 0.3 cm long, changing colour from pale green to brown. The hairs are whitish in appearance. The wasps of the sexual generation are sometimes known by the synonym ''Andricus fecundator'' forma ''pilosus'' (DvL 1982).Gall wasps
The gall wasp which emerges from the gall chamber in spring will always be an asexual female. But she will proceed to lay eggs on oak catkins, with a preference for ''Q. robur'' over ''Q. petraea'', which develop into 'hairy catkin galls'.Stubbs, F. B. Edit. (1986) ''Provisional Keys to British Plant Galls''. Pub. British Plant Gall Society. . P. 46. The oak artichoke gall is more common on bush or scrub than tree oaks.

Life cycle

The wasps emerging from the oak artichoke galls will be female; and these females will go on to lay a solitary egg in the male flowers of the oaks, which will cause the formation of the 'hairy catkin galls.' The flies that arise form these galls are of both sexes and the cycle then starts again after they have mated and eggs are laid in the oak buds. Once the oak artichoke gall has fallen to the ground the imago may leave the gall in the following spring, or may delay the emergence for 2–3 years. Galls may persist and exhibit opened scales curving outwards.

Gall-forming insects

Some herbivorous insects therefore create their own micro-habitats by forming usually highly distinctive plant structures called

s, made of plant tissue but controlled by the insect. Galls act as both the habitat, and food sources for the progeny of the gall wasp. The artichoke gall is formed entirely from the bud and is composed of nutritious starch and other tissues. Some galls act as "physiologic sinks", concentrating resources in the gall from the surrounding plant parts. Galls may also provide the insect with physical protection from predators.

Predators, inquilines and parasitoids

Mature galls are sometimes broken open by vertebrate predators to recover the larva or pupa. A number of insect inquilines live harmlessly within the oak artichoke gall and some of these, as well as ''Andricus '' itself, are

parasitised Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

by insects referred to as parasitoids. Some fungi may infect and kill the ''A. fecundator'' larvae. ''Andricus curvator'', the causative agent of the 'collared-bud gall' shows a marked preference for depositing its eggs on buds already colonised by ''A. fecundator''. This may represent an early phase in the development of the inquiline mode of life.

Infestations

Removing and destroying oak artichoke galls before they dry and the wasps emerge may help to reduce the infestation. While fairly large, and sometimes present in quite large numbers on scrub specimens, they cause no measurable harm.

References

External links

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A photograph of a section through an artichoke gall

{{Taxonbar, from=Q2135564 Cynipidae Gall-inducing insects Hymenoptera of Europe Insects described in 1840 Oak galls Taxa named by Theodor Hartig