Asphondylia sarothamni is a midge that causes galls to form on Broom (Cytisus scoparius). It is an example of an 'Ambrosia gall', where a fungus is introduced into the host plant by the midge. The inside of the gall is lined with mycelium, which is the actual larval food. 

There are two generations per year, each galling the Broom in a different way.  Early in the year the 1st generation galls form on the developing lateral flower buds of Broom. The adult midges that emerge from these galls go on to produce pod galls (2nd generation galls) - these may be quite variable. The midges emerge from the pod galls in June or July and oviposit into rudimentary buds, thus starting the cycle again. The eggs remain dormant in the buds until the following February or March. 

The galls are seen more frequently than the midges.

Several species cause galls in the buds or pods of Broom.  

Gall Adult

Checking for the presence of fungal mycelium inside an opened gall indicates an Ambrosia gall. 

Photographs of gall in situ.  Recommend that the gall is opened as well, to check for fungal hyphae.  

Wherever Broom (Cytisus scoparius) is found.

Generation 1 (bud galls) - Spring

Generation 2 (pod galls) - Summer  (full-sized in June)

Widespread but not well recorded in Britain.

Uncommon or under recorded in Leicestershire and Rutland.