In which book of Orson Scott Card's Ender series does the term "Formic" first appear?

I'm trying to find the first use of the term "Formic" in the Ender series. I don't believe it occurs in Ender's Game. The formics are always called the buggers. In Speaker for the Dead, they acknowledge that piggies is a derogatory term for the pequeninos, but that doesn't come up in Ender's Game. I'd really appreciate the help.