We owe this word to Sir Harold Nicolson, who introduced it to the world in the Spectator magazine in August 1952. In an issue of the same magazine later the same year, he described a doryphore as a “questing prig, who derives intense satisfaction from pointing out the errors of others.”
A writer in the New Yorker in 1989 described being taken out to lunch one day by the magazine’s editors: “They were rigidly abstemious, lest they fuddle their minds and give hostages to subsequent doryphores on returning to work.” (This writer follows a similar regime, with less success.) In 1996, Herb Caen commented in the San Francisco Chronicle: “For a doryphore, what is more delightful than a mistake in a correction?”
Sir Harold took it from French, in which it’s the usual name for the Colorado beetle, hence a pest. Doryphora was at one time the genus of the potato beetle, though its formal name today is Leptinotarsa decimlineata (decimlineata, ten-lined, in reference to its striped back). The old genus name was taken from Greek doruphoros, a spear-carrier, which echoes a one-time folk name for the insect in the US, the ten-striped spearman. The French presumably acquired their term for it from its old genus name.
As an aside, doryphore was French slang for the occupying German soldiers in World War Two. I’m told that the following passage is in Upton Sinclair’s Presidential Mission of 1947:
“What I wish,” declared Denis fervently, “is to drive the Nazi doryphores out of France, and indeed off the earth.”
“Très bien!” agreed the American. “But tell me, what is a doryphore?”
“Oh, you haven’t heard that? A doryphore is a potato bug, and we apply it to the Germans because they demand and get nearly all of the French potato crop. In our food-saving campaigns we send the school-children out to pick the bugs off the plants, and they have had the bright idea of carrying signs reading ‘Mort aux doryphores!’ The Germans can do nothing about that, so it gives delight to our people, who have not yet been entirely deprived of their sense of mischief.”
Later it became a derogatory term for tourists, much as the locals in Cornwall call them emmets (ants).