Diastrophus rubi is a gall wasp which affects Bramble (Rubus fruticosus agg.).  The galls is an elongated swelling, usually causing the stem to bend, with a bumpy surface, each bump containing a separate gall chamber.  Often the old, vacated galls are found with multiple exit holes; these can persist for many years. 

It is a bisexual species; after mating, fertilised eggs develop into females and unfertilised eggs into males.  Males are rare in some populations, and the species may be moving towards a parthenogenetic life-cycle where males are absent 

Lasioptera rubi is a gall-midge that causes similar swellings on bramble stems, 

Gall Adult

state the host, and provide photos