This is false.
The elegy, the dialogue, and the monologue are not three forms of the pastoral. Pastoral poems deal with an ideal society, usually in the countryside, where everything is beautiful and almost utopian. Dialogues and monologues are just ways of speaking (dialogue is between two or more people, monologue is when one person speaks), and elegies are sad poems, usually about somebody's death.
I'm not sure different forms of pastoral poems even exist because they all take the same form. :)
