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?