Sometimes we write a document in which we use a word in a way that differs from its more usual meaning. If you write that a location is filled with bugs, you need to put that word in quotation marks. Otherwise, people will be rushing to call an exterminator.
However, after the first use of bugs, omit the quotes for that word and for all other forms of it (bugged, bugging, etc.). You’ve already clued your readers in to the fact that you are referring to listening devices. No need to call an exterminator.