{{Short description|Species of wasp}} {{Speciesbox | image = Andricus quercuscalicis Quercus robur 02.jpg | image_caption = Mature gall on oak | genus = Andricus | species = quercuscalicis | authority = (Burgsdorf, 1783) }}
'''''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 wasps, 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 physical appearance of the gall== [[Image:Gallwespe bedient sich Eichel2.jpg|thumb|left|150px|Galls ''(upper left and right)'' formed on acorns on the branch of a pedunculate (or English) oak tree by the parthenogenetic generation ''Andricus quercuscalicis''.]]
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.<ref name="]Growth">{{Cite web |url=http://www.bugsandweeds.co.uk/galls%20p1.html#OakKnopper |title=Growth details. |access-date=2007-11-16 |archive-date=2010-09-23 |archive-url=https://web.archive.org/web/20100923181701/http://bugsandweeds.co.uk/galls%20p1.html#OakKnopper |url-status=dead }}</ref>
The word knopper derives from the German word 'Knoppe', meaning a kind of felt cap or helmet worn during the 17th century;<ref name="Tait">Tait, Norman & Pearl. ''The Spread of Knopper Gall Wasps into the Clyde area''. Glasgow Naturalist 2004, Vol. 24, pp. 131–132.</ref> also a small rounded protuberance, often decorative, such as a stud, a tassel or a knob.<ref name="knoppers">[http://www.wildyorkshire.co.uk/naturediary/docs/2002/9/23.html The origin of the name.]</ref>
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''.<ref name="Acorn cup">{{Cite web |url=http://www.bugsandweeds.co.uk/galls%20p1.html#AcornCup |title=Acorn Cup gall. |access-date=2007-11-16 |archive-date=2010-09-23 |archive-url=https://web.archive.org/web/20100923181701/http://bugsandweeds.co.uk/galls%20p1.html#AcornCup |url-status=dead }}</ref>
== Inquilines and parasitoids == A number of insect inquilines live harmlessly within the knopper gall and some of these, as well as ''A. quercuscalicis'' itself, are parasitised by insects referred to as parasitoids.<ref name="Randolph">Randolph, S. Parasitism by ''Cecidostiba fungosa'' (Hymenoptera: Pteromalidae) on the inquiline ''Synergus gallaepomiformis'' and observations on other community members of the agamic (knopper) galls of ''Andricus quercuscalicis'' in the Bristol area. Cecidology, 2003 (Vol. 18) (No. 2) p.42–50.</ref>
== Life-cycle == alt=A woody, irregular mass of plant tissue, open in half. A single (half) chamber can be seen, with a white curled larvae within.|thumb|A larvae of ''Andricus quercuscalicis'' in a gall formed in ''Quercus robur'' ''Andricus quercuscalicis'' (Burgsdorf, 1783) (Hymenoptera: Cynipidae)<ref name="Burgsdorf">[http://www.bioimages.org.uk/HTML/P3/P39901.phpis the first identification of the species.]{{dead link|date=October 2016 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> 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.)<ref name="Tait"/> and Turkey oak (''Quercus cerris'' L.).{{Cn|date=October 2025}}
The first phase, occurs in spring in small conical galls that form on the male catkins of the Turkey oak.<ref name="RHS">[http://www.rhs.org.uk/advice/profiles1005/knoppergall.asp Royal Horticultural Society website.] {{webarchive|url=https://web.archive.org/web/20071116050729/http://www.rhs.org.uk/advice/profiles1005/knoppergall.asp|date=November 16, 2007}}</ref> During this phase, females lay eggs without mating, and those eggs will produce both male and female wasps (parthenogenesis).<ref>{{Cite web |title=Glossary |url=https://gallformers.org/glossary |access-date=2025-09-13 |website=gallformers.org}}</ref><ref name=":1">{{Citation |last=Hurley |first=Brett P. |title=Gall Formers |date=2023 |work=Forest Entomology and Pathology |pages=457–493 |url=https://doi.org/10.1007/978-3-031-11553-0_14 |access-date=2025-09-13 |place=Cham |publisher=Springer International Publishing |isbn=978-3-031-11552-3 |last2=Dittrich-Schröder |first2=Gudrun |last3=Gevers |first3=Caitlin R.}}</ref> This bisexual generation mates, and the females lay their eggs in autumn. This second phase, called agamic generation, occurs in autumn.<ref name=":1" /> This phase occurs on pedunculate oaks. The galls created during this phase are commonly known as knopper galls.<ref name=":0">{{Cite journal |last=Schönrogge |first=Karsten |last2=Stone |first2=Graham N. |last3=Crawley |first3=Michael J. |last4=Schonrogge |first4=Karsten |date=February 1995 |title=Spatial and Temporal Variation in Guild Structure: Parasitoids and Inquilines of Andricus quercuscalicis (Hymenoptera: Cynipidae) in Its Native and Alien Ranges |url=https://doi.org/10.2307/3546037 |journal=Oikos |volume=72 |issue=1 |pages=51 |doi=10.2307/3546037 |issn=0030-1299|url-access=subscription }}</ref>
== Expansion outside of its native range == Since ''A''. ''quercuscalicis'' depends on Turkey oaks for its reproduction, the wasps were restricted to the range of Turkey oaks (south Eastern Europe). However, since the 17th century, Turkey oak has been planted throughout Europe, allowing for the wasp's range expansion.<ref name=":0" />
The records of the expansion of ''A''. ''quercuscalicis'' date as far as 1631, when it was recorded in eastern Germany. Great Britain and Ireland are the most recent territory gains of the species.<ref name=":0" />
=== Britain === 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,<ref name="Tait"/> ''A. quercuscalicis'' came from the continent to Devon via the Channel Islands, the first recorded sightings being in Devon in the 1950s. ''A. quercuscalicis'' appears to have arrived naturally from the continent, probably crossing the English Channel on high altitude wind currents.<ref name="Tait"/>
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.<ref name="Arival">[http://www.uknature.co.uk/KnopperGall-info.html Details of its spread to the UK.] {{webarchive |url=https://web.archive.org/web/20070809000059/http://www.uknature.co.uk/KnopperGall-info.html |date=August 9, 2007 }}</ref> Knopper galls were first noted at Canonbie in southern Scotland in 1995{{clarification needed|reason=a previous statement here gives the first appearance in Scotland as 2007 in North Lanarkshire - which is correct?|date=October 2021}} and their distribution is often restricted to old country and urban estates where the Turkey oak has been previously planted.<ref name="Tait"/>
The abnormal acorns develop during summer and the acorn is either wholly or partially replaced by the gall growth. 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.<ref name="Tait"/> The level of attack by the insect varies greatly from year to year.<ref name="RHS"/>
== See also == {{div col|colwidth=15em}} * Cola-nut gall * Gall * Oak apple * Oak marble gall * Oak artichoke gall * Red-pea gall{{div col end}}
== References == {{Reflist}} *
== External links == {{Commonscat}} * [https://web.archive.org/web/20130523125445/http://british-galls.org.uk/ British Plant Gall Society] * {{cite encyclopedia | title=Gall | encyclopedia=Infoplease Encyclopedia | url=http://www.infoplease.com/ce6/sci/A0820047.html | accessdate = 10 November 2007}} * {{cite web | title=Common oak gall | publisher=University of Kentucky Department of Entomology | url=http://www.uky.edu/Ag/Entomology/entfacts/trees/ef408.htm | accessdate = September 11, 2006| archiveurl= https://web.archive.org/web/20060913044856/http://www.uky.edu/Ag/Entomology/entfacts/trees/ef408.htm |archive-date=13 September 2006 |url-status= live}} *[http://www.uksafari.com/galls4.htm The UK Safari site on Knopper galls.] * [https://web.archive.org/web/20120728181320/http://www.bioimages.org.uk/html/p3/p39901.php A photograph of a longitudinal section of the gall.] * [https://www.youtube.com/watch?v=hcrbRnUKg80&t=7s Video footage of Scottish Galls]
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Category:Cynipidae Category:Gall-inducing insects Category:Hymenoptera of Europe Category:Insects described in 1783 Category:Oak galls Category:Acorns