''Chirosia betuleti'' is a species of fly, which causes knotting gall in ferns. The

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. Plant galls are abnormal outgrowths of plant tissues, similar to benign tumors or war ...

develops in the terminal shoots of ferns, such as broad buckler fern ('' Dryopteris dilatata''), male fern ('' Dryopteris filix-mas''), lady fern ('' Athyrium filix-femina''), and ostrich fern ('' Matteuccia struthiopteris)''.Stubbs, F. B. Edit. (1986) ''Provisional Keys to British Plant Galls''. Pub. Brit Plant Gall Soc. ., p. 80Redfern, Margaret & Shirley, Peter (2002). ''British Plant Galls. Identification of galls on plants & fungi.'' AIDGAP. Shrewsbury : Field Studies Council. , p. 288BioStor
Retrieved: 2011-07-28

The physical appearance of the galls

The fly larva mines the leaves and stems of the fern's frond at the apex. The tip of the frond rolls upwards into a loose, obvious knot or mop-head structure involving many pinnae; inside, a white larva mines along the rachis, eating the

trichomes Trichomes (; ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plant ...

, causing it to coil. Usually, only one larva is present in the leaf tip, sometimes two. An elongated white egg shell is visible at the centre of the mass.Leaf and Stem Mines
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Lifecycle

Eggs are laid in the unfurling fronds and the hatched larvae feed on the trichomes in the groove of the rachis, causing the frond to curl inwards. The pupae drop from the gall and remain from autumn and winter to emerge in the spring. Galling rates up to nine fronds in 13 on a single plant have been noted.

Distribution

The knotting gall is found in Cornwall, Wiltshire, Worcester, Hants, Norfolk, Warwickshire, Berkshire, Cardiganshire, Cheshire, Denbighshire, East Norfolk, Suffolk, Easterness, Elgin, Flintshire, North Ayrshire, Herefordshire, Merionethshire, Perth, Yorkshire, Montgomeryshire, Lincolnshire, Somerset, Oxfordshire, Shropshire, Devon, Hampshire, Yorkshire, Stafford, Surrey, Gloucestershire, Kent, Suffolk, and Worcestershire. As shown, the knotting gall has been recorded throughout the United Kingdom, in the Netherlands, the Czech Republic, Denmark, Finland, France, Germany, Italy, Norway, Poland, Russia – north and north-west, Slovakia, Spain, and Sweden.

Parasitoids

Braconid wasps of the genus ''Aphaereta'' and eulophid wasps of the genera '' Dimmockia'' and '' Elachertus'' have been identified as

parasitoids In evolutionary ecology, a parasitoid is an organism that lives in close association with its host (biology), host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionarily stable str ...

of ''C. betuleti''.

The physical appearance of the galls

Lifecycle

Distribution

Parasitoids

References

Further reading