The rhododendron leafhopper (Graphocehala fenndui) is described in my text book as having been introduced to Britain in the early 1900's from the United States. It does not expand on this statement so it is unclear whether it was an intentional or accidental introduction. One source on the internet says the first record was from Chobham in Surrey in 1934 so it appears that the bug found its own way here on imported rhododendrons for garden planting.
It is a large species for a leafhopper but still a pretty small insect being less than half an inch in length. It is primarily green with red streaks and in the United States it is known as the scarlet and green leafhopper; it is pretty much unmistakable. It lives exclusively on rhododendron from which it sucks sap from the plant. Often, several will be found together on one leaf.
Although an alien species it is not considered invasive despite having done well here. As swathes of rhododendron are cleared from our countryside so the numbers of this little creature will decline too. It is thought to carry a fungus from one plant to another but between them, the insect and the fungus, they seem to have little impact on controlling rhododendron organically.