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"A Nature Observer′s Scrapbook"

Galls Page 2
- galls found on herbaceous, soft stemmed plants.




Ground Ivy 
'Lighthouse' galls

So what is a gall? A general definition states that :- "A gall is an abnormal growth produced by a plant or other host under the influence of another parasitic organism. It involves enlargement and/or proliferation of the host cells and provides both shelter and food or nutrients for the invading organism. The association between the causal agent and the host is usually quite specific."

....... which means that specific causers are very selective about the plant species they associate with.

The scientific name given to a gall very often reflects the name of the causer - whether that be bacteria, fungus, nematode, insect or mite.

Galls forming on plant stems tend to take on a hard woody form, while those on leaves can be softer and take after the surface characteristics of the leaf - smooth/hairy, dull/shiny.




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Urophora cardui Urophora cardui Grubs inside the gall chamber

Creeping thistle gall

Urophora cardui


Since the northern limit of this particular causal fly (Diptera: Tephritidae: Urophora cardui) is thought to be the English Midlands, it was perhaps a very fortunate find to come across this well established colony.


But, in September 2003, in a large patch of Creeping thistle (Cirsium arvense) about one in every twenty plants seemed to be affected. It was obviously a well established infestation since there were galls in all stages of development, from the fresh green stage (upper right) through to the old and woody stages (middle right).


One month later, I found great difficulty in cutting through a gall which had become very hard and woody compared to the soft stem tissue of normal wilting plants in the close vicinity.


A gall found on dry withered stems in March was so hard that it could not be cut through 'in the hand'. It was eventually split against a post and revealed three larvae in separate chambers (lower image). It is quite possible that more slices would have revealed more chambers.


Since gall grubs are subject to parasite attacks from other insects, it could be that the rapid hardening of the gall chamber is some measure of defence against such attacks.



DateSighting
27.09.2003Benniworth Springs, conservation area, large colony.
11.09.2004Benniworth Springs conservation area, only a very few this year.
20.03.2005Benniworth Springs conservation area, several galls still in evidence on last year's dead growth.
28.08.2005 A few new galls at the Benniworth site, none seen anywhere else.
03.09.2006 More galls at the Benniworth site than last year.


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Ground Ivy gall

Ground Ivy (Glechoma hederacea) gall

Liposthenes glechomae

These galls can range from 5 to 20mm in diameter

If hidden from light by surrounding vegetation the gall will remain green but, when exposed to sunlight will take on a russet colour. The gall is covered with short bristles.

The causer is a gall wasp from the Cynipidae family and there will usually be one larva per gall.

The plant is described under Ground Ivy on the Plants page.


DateSighting
19.08.2004 Found by narrow gate to Hay Meadow.


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Ground Ivy 
'Lighthouse' gall Ground Ivy 'Lighthouse' gall
- and then they were gone

Ground Ivy 'Lighthouse' gall

Rondaniola busaria

These galls may be found singly or several on one leaf. I found one leaf with 17 galls on it and it was so crowded and distorted as to make the leaf unrecognisable.

The bristly little individual galls - only about 4mm in height but easy to see why they are described as 'lighthouse' galls, each contain one white larva of the parasitic fly, Diptera: Cecidomyiidae: Rondaniola bursaria.

Since the leaves of Ground Ivy are not shed as those of trees are, as the grubs reach maturity individual galls detach from the leaf and fall to the ground to allow the larvae to pupate through the winter in the safety of the ground litter. The fallen galls leave behind very clean neat holes in the leaf which are much more conspicuous than were the galls themselves. It was the damaged leaves that attracted my attention.

The galls are to be found from August to early October.



DateSighting
04.10.2005 Found in a well established clump of Ground Ivy at the base of a hawthorn hedge.
24.09.2006 Found again, only 20m from last years site.


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Germander Speedwell

Germander Speedwell

Jaapiella veronicae

When I first noticed this in June 2006, it was so common that I initially assumed that it was common natural growth.

However, the tiny orange bodied, long legged gall midge, Jaapiella veronicae, is responsible for laying it's eggs in the terminal buds of Speedwell plants, most commonly the Germander speedwell, Veronica chamaedrys. This causes the young leaves to become thickened and deformed allowing a pouch to develop and accomodate one or two orange-red larvae.



DateSighting
25.06.2006 Locally very common


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Sweet Violet
leaf gall

Sweet Violet leaf gall

Dasineura odoratae ?

Some confusion currently exists over definitive identification of gall causers within the Viola family of plants but the scientific name reflects that this is one of the Dasineura group of gall flies which infects the Viola odorata plant in the manner shown.

The small gall fly larva causes the leaf edge to curl upwards and roll over to thicken and form a protective shelter. The underside of the leaf which is normally only slightly pubescent at best, becomes very 'furry' and, considering the normal delicate leaf structure, presents a surprisingly firm refuge for the developing larva.

The image shows a leaf with two outer leaf margins 'galled' alongside a normal, unaffected leaf. Seasonal winter die-back in plant cover at the base of a hawthorn hedge revealed quite a cluster of affected leaves within this long established Viola odorata plant colony.

This gall is considered to be relatively common in Southern England and East Anglia.



DateSighting
02.03.2006 Quite a colony of affected leaves found on a roadside verge
22.01.2008 A few affected leaves found at same location as in 2006.


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Tetramesa hyalipennis Tetramesa hyalipennis Tetramesa hyalipennis larva

Couch grass gall, 1

Tetramesa hyalipennis


Identification of this gall caused me a few problems because the growth of the gall tends to inhibit the formation of the inflorescence and seed head and that made identification of the grass - well, for me, more difficult.


The gall proved to be locally prevalent in the Couch grass, Elymus (Elytrigia) repens, growing in sheltered hedgerows. I have yet to see it on open verges - but, these are subject to mid summer management cutting and mowing which could mean that the couch grass is not mature enough when the causer is egg laying.


The causer is a tiny wasp, Hymenoptera: Eurytomidae: Tetramesa hyalipennis.


The 5mm larva was found in mid October, in a single chamber within the base of a swollen gall surrounded by white 'frass' (digested plant residue!).



DateSighting
12.10.2003Hay Meadow, western hedge.
21.08.2004Hay Meadow, 2 specimens NW corner, 1 in NE corner.
13.09.2004Hay Meadow, 15 specimens in N and E hedgerows.
19.08.2006Hay Meadow, several specimens in NW corner.
19.10.2008Hay Meadow, 54 specimens in 100m NW western hedge.


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Chlorops pumilionis

Couch grass gall, 2

Chlorops pumilionis

Initially one solitary plant in a hawthorn hedgerow was found to be affected, with two closely coupled leaf joints showing the same signs of attack.

The leaf joints appear swollen, produce a small cluster of stunted, distorted leaves and small club, root-like growths protrude from the swellings.

Each swelling houses a chamber containing one pale larva of the fly, Diptera: Chloropidae, Chlorops pumilionis - which can be seen on this link to the Flies Page 2..

Couch is not the only member of the grass family to be affected. It can be a serious pest in Barley crops.


DateSighting
26.09.2004Found in NW corner of Hay Meadow hedgerow, TF 3045 6611.
20.10.2004Three more occurences in NW corner of North Paddock fence line, TF 3043 6622.


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Cleavers gall

Cleavers (Galium aparine) gall

Dasineura aparines
previously thought to be Aculus anthobius

This gall was previously thought to be caused by the mite 'Aculus anthobius' but it is now considered more likely to be caused by the gall fly Dasineura aparines. Positive identification must await expert examination.

The effect on the plant is to stunt stem growth near the growing tip without affecting the leaves, flowers and fruit which appear to develop normally. The plant eventually recovers and sends out a new stem from below the infestation.


DateSighting
16.07.2004Several examples found on the Galium aparine in the NW corner of Hay Meadow hedge.
26.07.2005Unlike other galls which seem to be scarce this year, this one appears to be widespread.


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Nettle Leaf gall grub of the gall causer predatory gall grub

Nettle Leaf gall

Dasineura urticae

The common stinging nettle, Urtica dioica and the less common annual stinging nettle, Urtica urens, can both be galled by the small Cecid fly, Dasineura urtica. It lays its eggs in the base of the nettle leaf or in the main leaf veins. The larvae then cause a 'pouch' to form in the leaf structure and from the 'supposed' safety of this enclosed retreat, they consume the inner tissues of the leaf.

But, in the diverse world of nature, rarely is anything safe. Other predatory Cecid flies will often lay their eggs in these leaf pouches and on hatching these larvae predate on the original gall causer grubs.

So, if you care to brave the nettles stinging hairs and investigate the inner contents of the pouch you may find one or more tiny white maggot like grubs (these will be the original gall causing grubs), and, perhaps, also pink, orange or red predatory 'inquiline' grubs.

Mature flies will eventually escape through tiny slits in the upper surface of the gall.

The middle image is of an almost mature 2.5mm grub of the gall causer. 'Almost mature' because it rather looks from its partly transparent body as though the red predatory grub found with it has been feeding from it.

The lower image is of a 2.5mm predatory grub which, as one might expect, was much more active than its host.



DateSighting
30.09.2006 More common on hedgerow nettles than on isolated nettles.


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Nettle Rust Nettle Rust

Nettle Rust

Puccinia urticata

When I took the upper image I thought it was a caterpillar. It was only when I enlarged the image that I realised how wrong I was and went back to take a closer look.

This orange or reddish nettle rust gall can cause swelling, distortion and discoloration of stems or leaves on either Stinging Nettle (Urtica dioica) or Small Nettle (U. urens).

It is caused by the fungus Puccinia urticata. It is not uncommon for rust fungus to develop on two different host plant species. In this case, the early stages of development takes place on nettles. After the fugus spores are released their further development takes place on Carex sedges.

It is curious that the stem and leaf images seen here - the only instances that I have ever seen of this gall - were taken four years apart and yet within some 100m of each other.



DateSighting
03.06.2004NW end of hay meadow hedge. One occurence of the stem fungus found.
08.05.2008NW end of hay meadow hedge. Only the one occurence of the leaf fungus was found.
20.05.2009At NW corner post of hay meadow hedge, stem and leaf galls found.



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