Gall midges
 
Plant galls are abnormal growths produced by a plant in response to the presence of a gall-forming organism.  Many insects and mites, as well as some fungi and bacteria, are capable of causing galls.  We have a special page introducing plant galls on this website here.  Most of the fly-induced galls seen in a garden will have been caused by tiny flies, known as gall midges, in the Cecidomyiidae family. Flies in this family have hairy wings and long antennae. Globally, this is a very large family, and a recent study by Hebert et. al. (2014)1 used DNA barcoding techniques to estimate that there are over 16,000 species in Canada alone. Generally, Canada is home to about 1% of species across the world's fauna, which implies that the Cecidomyiidae could contain 1.8 million species worldwide, making it the most diverse Family in the animal kingdom.
 
Species in Britain and Ireland
 
There are about 650 species of gall midge in Britain and Ireland.  Most develop in plant galls but some feed as larvae on fungi or are predators of other insects. Some species cause galls on garden plants, such as pear fruitlet gall midge, Contarinia pyrivora; pear leaf gall midge, Dasineura pyri on pear leaves; blackcurrant gall midge, Dasineura tetensi, on blackcurrant leaves; violet gall midge, Dasineura affinis, on violet leaves; gleditsia gall midge, Dasineura gleditchiae, on Gleditsia triacanthos leaves; false acacia gall midge, Obolodiplosis robiniae, on Robinia pseudoacacia leaves; yew gall midge, Taxomyia taxi, on yew shoot tips; daylily gall midge, Contarinia quinquenotata, on Hemerocallis flower buds.
 
 
Two unidentified gall midge adults.  There are many more photos of galls and larvae than of the tiny adult midges!
 
Biology
Gall midge larvae cause galls on various parts of a plant, such as the leaves, shoot tips, flowers and developing fruits. The larvae secrete chemicals that prevent the normal development of the host plant’s tissues.  Instead, the plant produces gall tissues that enclose the gall midge larvae and provide the larvae with a concealed place in which they feed.
 
The galls can take the form of folded or rolled leaf margins, sometimes abnormally swollen, as with the pear leaf, violet, gleditsia and false acacia gall midges.  Daylily gall midge causes abnormally swollen flower buds that fail to open. Pear fruitlet gall midge causes abnormal growth of the newly set fruitlets, causing them to blacken and drop off in early summer.  Yew gall midge stunts the growth of shoot tips, with the larva developing within a rosette of leaves.  Adult gall midges are short-lived and do not feed.
 
 
Galls formed by gall midges Left: Hemerocallis gall midge Contarinia quinquenotata Centre: Pear fruitlet gall midge Contarinia pyrivora  Right: Yew gall midge Taxomyia taxi gall
 
 
Life cycle
Adult gall midges emerge and lay eggs on the appropriate part of their host plants at a time of year when the plants’ growth is at a suitable stage for the galls to develop.  The larvae feed inside the galls that they have helped to create.  When fully fed, the larvae either pupate within the galls, or in some species they will go into the soil to pupate.  Most species have a single generation a year but some, such as the violet and blackcurrant gall midges, will have two or three generations during the summer.  Gall midges mostly overwinter as pupae.
 
Role of gall-forming flies in gardens
Some species of gall midges are damaging pests of garden plants but most are associated with wild flowers and forest trees where they cause no significant damage.  One species of ‘gall’ midge, Aphidoletes aphidimyza, has larvae that prey on aphids and is commercially available as a biological control for use in glasshouses.
 
 
Predatory gall midge Aphidoletes aphidimyza  Left: adult fly (probable identification) Right: larva eating aphids.
 
Reference:
1.  Hebert PDN, Ratnasingham, S, Zakharov EV, Telfer AC, Levesque-Beaudin V, Milton MA, Pedersen S, Jannetta P, deWaard JR.  (2016)   Counting animal species with DNA barcodes: Canadian insects. Phil. Trans. R. Soc. B 371: 20150333.   Viewable here 
 
Other sources of information
Website
Web site of the British Gall Society
RHS information on pear midge
CABI information on pear leaf midge
RHS information on blackcurrant gall midge
RHS information on daylily gall midge
 
 
Books
Chinery, M. (2011) Britain’s Plant Galls – a photographic guide. WildGuides Ltd
Redfern, M. Shirley, P. Bloxham M. (2023) British Plant Galls. Third Edition, A Field Studies Council AIDGAP key
 
 
Page drafted by Andrew Salisbury, reviewed by Andrew Salisbury, edited by Steve Head
 
 
Gall midges
 
Plant galls are abnormal growths produced by a plant in response to the presence of a gall-forming organism.  Many insects and mites, as well as some fungi and bacteria, are capable of causing galls.  We have a special page introducing plant galls on this website here.  Most of the fly-induced galls seen in a garden will have been caused by tiny flies, known as gall midges, in the Cecidomyiidae family. Flies in this family have hairy wings and long antennae. Globally,this is a very large family, and a recent study by Hebert et. al. (2014)1 used DNA barcoding techniques to estimate that there are over 16,000 species in Canada alone. Generally, Canada is home to about 1% of species across the world's fauna, which implies that the Cecidomyiidae could contain 1.8 million species worldwide, making it the most diverse Family in the animal kingdom.
 
Species in Britain and Ireland
 
There are about 650 species of gall midge in Britain and Ireland.  Most develop in plant galls but some feed as larvae on fungi or are predators of other insects. Some species cause galls on garden plants, such as pear fruitlet gall midge, Contarinia pyrivora; pear leaf gall midge, Dasineura pyri on pear leaves; blackcurrant gall midge, Dasineura tetensi, on blackcurrant leaves; violet gall midge, Dasineura affinis, on violet leaves; gleditsia gall midge, Dasineura gleditchiae, on Gleditsia triacanthos leaves; false acacia gall midge, Obolodiplosis robiniae, on Robinia pseudoacacia leaves; yew gall midge, Taxomyia taxi, on yew shoot tips; daylily gall midge, Contarinia quinquenotata, on Hemerocallis flower buds.
 
 
Gall midges
 
Plant galls are abnormal growths produced by a plant in response to the presence of a gall-forming organism.  Many insects and mites, as well as some fungi and bacteria, are capable of causing galls.  We have a special page introducing plant galls on this website here.  Most of the fly-induced galls seen in a garden will have been caused by tiny flies, known as gall midges, in the Cecidomyiidae family. Flies in this family have hairy wings and long antennae. Globally, this is a very large family, and a recent study by Hebert et. al. (2014)1 used DNA barcoding techniques to estimate that there are over 16,000 species in Canada alone. Generally, Canada is home to about 1% of species across the world's fauna, which implies that the Cecidomyiidae could contain 1.8 million species worldwide, making it the most diverse Family in the animal kingdom.
 
Species in Britain and Ireland
 
There are about 650 species of gall midge in Britain and Ireland.  Most develop in plant galls but some feed as larvae on fungi or are predators of other insects. Some species cause galls on garden plants, such as pear fruitlet gall midge, Contarinia pyrivora; pear leaf gall midge, Dasineura pyri on pear leaves; blackcurrant gall midge, Dasineura tetensi, on blackcurrant leaves; violet gall midge, Dasineura affinis, on violet leaves; gleditsia gall midge, Dasineura gleditchiae, on Gleditsia triacanthos leaves; false acacia gall midge, Obolodiplosis robiniae, on Robinia pseudoacacia leaves; yew gall midge, Taxomyia taxi, on yew shoot tips; daylily gall midge, Contarinia quinquenotata, on Hemerocallis flower buds.
 
 
Two unidentified gall midge adults.  There are many more photos of galls and larvae than of the tiny adult midges!
 
Biology
Gall midge larvae cause galls on various parts of a plant, such as the leaves, shoot tips, flowers and developing fruits. The larvae secrete chemicals that prevent the normal development of the host plant’s tissues.  Instead, the plant produces gall tissues that enclose the gall midge larvae and provide the larvae with a concealed place in which they feed.
 
The galls can take the form of folded or rolled leaf margins, sometimes abnormally swollen, as with the pear leaf, violet, gleditsia and false acacia gall midges.  Daylily gall midge causes abnormally swollen flower buds that fail to open. Pear fruitlet gall midge causes abnormal growth of the newly set fruitlets, causing them to blacken and drop off in early summer.  Yew gall midge stunts the growth of shoot tips, with the larva developing within a rosette of leaves.  Adult gall midges are short-lived and do not feed.
 
 
Life cycle
Adult gall midges emerge and lay eggs on the appropriate part of their host plants at a time of year when the plants’ growth is at a suitable stage for the galls to develop.  The larvae feed inside the galls that they have helped to create.  When fully fed, the larvae either pupate within the galls, or in some species they will go into the soil to pupate.  Most species have a single generation a year but some, such as the violet and blackcurrant gall midges, will have two or three generations during the summer.  Gall midges mostly overwinter as pupae.
 
Role of gall-forming flies in gardens
Some species of gall midges are damaging pests of garden plants but most are associated with wild flowers and forest trees where they cause no significant damage.  One species of ‘gall’ midge, Aphidoletes aphidimyza, has larvae that prey on aphids and is commercially available as a biological control for use in glasshouses.
 
 
Galls formed by gall midges Above left: hemerocallis gall midge Contarinia quinquenotata Above right: Pear fruitlet gall midge Contarinia pyrivora  Left: Yew gall midge Taxomyia taxi 
Predatory gall midge Aphidoletes aphidimyza  Left: adult fly (probable identification) Right: larva eating aphids.
 
Reference:
1.  Hebert PDN, Ratnasingham, S, Zakharov EV, Telfer AC, Levesque-Beaudin V, Milton MA, Pedersen S, Jannetta P, deWaard JR.  (2016)   Counting animal species with DNA barcodes: Canadian insects. Phil. Trans. R. Soc. B 371: 20150333.   Viewable here 
 
Other sources of information
Website
Web site of the British Gall Society
RHS information on pear midge
CABI information on pear leaf midge
RHS information on blackcurrant gall midge
RHS information on daylily gall midge
 
 
Books
Chinery, M. (2011) Britain’s Plant Galls – a photographic guide. WildGuides Ltd
Redfern, M. Shirley, P. Bloxham M. (2023) British Plant Galls. Third Edition, A Field Studies Council AIDGAP key
 
 
Page drafted by Andrew Salisbury, reviewed by Andrew Salisbury, edited by Steve Head
 
 
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