Graphocephala fennahi, also known as the Rhododendron Leafhopper, is a species that belongs to the family Cicadellidae.
It is a small leafhopper (length 8-10 mm) and it is named as such because it feeds on the sap of rhododendrons.
It is native to the USA and was introduced to Great Britain in the 1930's and continental Europe in the 1970's.
Adults can be found from mid-summer until quite late in the autumn, laying eggs in the leaf buds which hatch the following spring.

In my yard, Hilversum, The Netherlands, 17 August 2013