Not long ago I noticed, and unfortunately failed to capture, a reference to a study which discussed the responses of bees to fresh outflows of copal. Copal is a natural exudate resin from several species of tropical trees including those of the genus Copaifera. As I recall, bees become intensely hostile and aggressive, even to members of their own hive, when this resin resin is flowing. Can anyone lead me to studies which treat this relationship?