Knopper gall
Encyclopedia
Andricus quercuscalicis is a gall wasp species inducing Knopper galls.
Knopper galls develop as a chemically induced distortion of growing acorns on Pedunculate Oak
(Quercus robur L.) trees, caused by gall wasp
s, which lay eggs in buds with their ovipositor
. The gall
thus produced can greatly reduce the fecundity
of the oak host, making this gall potentially more of a threat to the reproductive ability of the tree than those that develop on leaves, buds, stems, etc. The Turkey Oak
(Quercus cerris L.), introduced into Britain in 1735, is required for the completion of the life cycle of the gall. The Knopper is a recent introduction to the British Isles, first arriving in the 1960s and now found throughout England, Wales and as far north as Scotland; first occurring for example in 2007 at Eglinton Country Park
in North Ayrshire
.
The large 2 cm gall growth appears as a mass of green to yellowish-green, ridged, and at first sticky plant tissue on the bud of the oak, that breaks out as the gall between the cup and the acorn. If only a few grubs are developing within, then it may appear only as a group of bland folds. Where several grubs are competing for space the shape may become much more contorted, with several tightly bunched galls.
The word knopper derives from the German word 'knoppe' meaning a kind of felt cap or helmet worn during the 17th-century; also a small rounded protuberance, often decorative, such as a stud, a tassel or a knob.
Although normally distinctive the knopper gall can, under some growth conditions, be mistaken for the acorn cup gall
, caused by the gall wasp Andricus grossulariae
.
s live harmlessly within the knopper gall and some of these, as well as A. quercuscalicis itself, are parasitised by insects referred to as parasitoids.
(Quercus cerris L.). Therefore, as with most oak gall wasps, this species has alternate sexual and parthenogenetic (all female) generations. The sexual generation develops in spring in small conical galls that form on the male catkins of the Turkey Oak.
Woodway House
gardens in Devon
have both the required host species and indeed Woodway House was one of the first places in Devon to record and send off for research purposes specimens of both life-cycle stages of this invasive species. Long known in western and northern Europe, having spread from southern and eastern Europe over the last 400 years; A. quercuscalicis came from the continent to Devon via the Channel Islands
, the first recorded sightings being in Devon
shire in the 1950s. A. quercuscalicis appears to have arrived naturally from the continent, probably crossing the English Channel on high altitude wind currents.
In 1979, A. quercuscalicis underwent a population explosion in England and for a time there was concern that it would seriously affect acorn fertility and thus the future of England's most iconic tree. This has not been the case, and control is regarded as unnecessary. Knopper galls were first noted at Canonbie
in southern Scotland in 1995 and their distribution is often restricted to old country and urban estates where the Turkey oak has been previously planted.
The abnormal acorns develops during summer and the acorn is either wholly or partially replaced by the gall growth. As previously stated, the knoppers become woody and brown in early autumn, after which they fall from the tree and the adult sexual female gall wasp emerges through a vent in the top of the gall in spring. The level of attack by the insect varies greatly from year to year.
Knopper galls develop as a chemically induced distortion of growing acorns on Pedunculate Oak
Pedunculate Oak
Quercus robur is commonly known as the Pedunculate Oak or English oak. It is native to most of Europe, and to Anatolia to the Caucasus, and also to parts of North Africa.-Taxonomy:Q...
(Quercus robur L.) trees, caused by 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...
s, which lay eggs in buds with their ovipositor
Ovipositor
The ovipositor is an organ used by some animals for oviposition, i.e., the laying of eggs. It consists of a maximum of three pairs of appendages formed to transmit the egg, to prepare a place for it, and to place it properly...
. The 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...
thus produced can greatly reduce the fecundity
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
of the oak host, making this gall potentially more of a threat to the reproductive ability of the tree than those that develop on leaves, buds, stems, etc. The Turkey Oak
Turkey Oak
Quercus cerris, the Turkey oak is an oak native to southern Europe and Asia Minor. It is the type species of Quercus sect. Cerris, a section of the genus characterised by shoot buds surrounded by soft bristles, bristle-tipped leaf lobes, and acorns that usually mature in 18...
(Quercus cerris L.), introduced into Britain in 1735, is required for the completion of the life cycle of the gall. The Knopper is a recent introduction to the British Isles, first arriving in the 1960s and now found throughout England, Wales and as far north as Scotland; first occurring for example in 2007 at Eglinton Country Park
Eglinton Country Park
Eglinton Country Park is located in the grounds of the old Eglinton Castle estate, Kilwinning, North Ayrshire, Scotland . Eglinton Park is situated in the parish of Kilwinning, part of the former district of Cunninghame, and covers an area of 400 hectares...
in North Ayrshire
North Ayrshire
North Ayrshire is one of 32 council areas in Scotland with a population of roughly 136,000 people. It is located in the south-west region of Scotland, and borders the areas of Inverclyde to the north, Renfrewshire to the north-east and East Ayrshire and South Ayrshire to the East and South...
.
The physical appearance of the gall
The word knopper derives from the German word 'knoppe' meaning a kind of felt cap or helmet worn during the 17th-century; also a small rounded protuberance, often decorative, such as a stud, a tassel or a knob.
Although normally distinctive the knopper gall can, under some growth conditions, be mistaken for the acorn cup gall
Andricus grossulariae
Andricus grossulariae is a gall wasp species inducing agamic acorn cup or gooseberry galls on oak tree acorn cups and sexual phase galls on catkins...
, caused by the gall wasp Andricus grossulariae
Andricus grossulariae
Andricus grossulariae is a gall wasp species inducing agamic acorn cup or gooseberry galls on oak tree acorn cups and sexual phase galls on catkins...
.
Inquilines and parasitoids
A number insect inquilineInquiline
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 live harmlessly within the knopper gall and some of these, as well as A. quercuscalicis itself, are parasitised by insects referred to as parasitoids.
Life-cycle and arrival in Britain
Andricus quercuscalicis (Burgsdorf, 1783) (Hymenoptera: Cynipidae) is a small gall wasp with an obligate two-phase life-cycle that requires both Pedunculate Oak (Q. robur L.) (or occasionally Sessile oak Q.petraea L.) and Turkey OakTurkey Oak
Quercus cerris, the Turkey oak is an oak native to southern Europe and Asia Minor. It is the type species of Quercus sect. Cerris, a section of the genus characterised by shoot buds surrounded by soft bristles, bristle-tipped leaf lobes, and acorns that usually mature in 18...
(Quercus cerris L.). Therefore, as with most oak gall wasps, this species has alternate sexual and parthenogenetic (all female) generations. The sexual generation develops in spring in small conical galls that form on the male catkins of the Turkey Oak.
Woodway House
Woodway House
Woodway House is in Teignmouth, South Devon, England. It was at one time a farm on lands held by the Bishops of Exeter. In around 1815 a thatched 'cottage' in the 'cottage orne' style of Horace Walpole's Thames-side villa, Strawberry Hill, was built here by Captain James Spratt R.N.Walpole built...
gardens in Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
have both the required host species and indeed Woodway House was one of the first places in Devon to record and send off for research purposes specimens of both life-cycle stages of this invasive species. Long known in western and northern Europe, having spread from southern and eastern Europe over the last 400 years; A. quercuscalicis came from the continent to Devon via the Channel Islands
Channel Islands
The Channel Islands are an archipelago of British Crown Dependencies in the English Channel, off the French coast of Normandy. They include two separate bailiwicks: the Bailiwick of Guernsey and the Bailiwick of Jersey...
, the first recorded sightings being in Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
shire in the 1950s. A. quercuscalicis appears to have arrived naturally from the continent, probably crossing the English Channel on high altitude wind currents.
In 1979, A. quercuscalicis underwent a population explosion in England and for a time there was concern that it would seriously affect acorn fertility and thus the future of England's most iconic tree. This has not been the case, and control is regarded as unnecessary. Knopper galls were first noted at Canonbie
Canonbie
Canonbie is a small village in Dumfries and Galloway in south west Scotland, six miles south of Langholm and two miles north of the Anglo-Scottish border. It is on the A7 road from Carlisle to Edinburgh, and the River Esk flows through it...
in southern Scotland in 1995 and their distribution is often restricted to old country and urban estates where the Turkey oak has been previously planted.
The abnormal acorns develops during summer and the acorn is either wholly or partially replaced by the gall growth. As previously stated, the knoppers become woody and brown in early autumn, after which they fall from the tree and the adult sexual female gall wasp emerges through a vent in the top of the gall in spring. The level of attack by the insect varies greatly from year to year.
See also
- GallGallGalls 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...
- Oak appleOak appleOak apple is the common name for a large, round, vaguely apple-like gall commonly found on many species of oak. Oak apples range in size from 2-5cm. Oak apples are caused by chemicals injected by the larva of certain kinds of gall wasp in the family Cynipidae. The adult female wasp lays single...
- Oak marble gallOak marble gallOak 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...
- Oak artichoke gallOak artichoke gallOak artichoke galls, oak hop galls, larch-cone galls or hop strobiledevelop as a chemically induced distortion of leaf axillary or terminal buds on Pedunculate Oak or Sessile Oak trees, caused by the parthenogenetic gall wasp Andricus fecundator, which lays single eggs within leaf buds using...
- Pineapple gall
- Rose bedeguar gallRose bedeguar gallThe Rose bedeguar gall, Robin's pincushion gall, or Moss galldevelops as a chemically induced distortion of an unopened leaf axillary or terminal buds mostly on Field Rose or Dog rose shrubs, caused by the parthenogenetic hymenopteran gall wasp , previous synonyms are D...
- Cola-nut gallCola-nut gallCola-nut galls develop as a chemically induced distortion of leaf axillary or terminal buds on Pedunculate Oak or Sessile Oak trees, caused by the agamic gall wasp Andricus lignicola which lays single eggs within leaf buds using their ovipositor. A previous name or synonym for the species A....
- Red-pea gallRed-pea gallThe Red-pea gall or Red Currant gall develops as a chemically induced distortion arising from the underside of the mid-rib of a vein on Quercus species and it is attached by a short stalk or peduncle...
- Alder tongue gallAlder tongue gallTaphrina alni is a fungal plant pathogen that causes Alder tongue gall, a chemically induced distortion of female alder catkins ....
- Eriophyes tiliae
Sources
- Redfern, Margaret & Shirley, Peter (2002). British Plant Galls. Identification of galls on plants & fungi. AIDGAP. Shrewsbury : Field Studies Council. ISBN 1-85153-214-5.