I need to send email from template to task creator when project task reach particular stage?  how do I do that?

in "project.task.type" model i created field 

creator_mail_template_id = fields.Many2one(    
    'mail.template', 
    string='Task Creator Email Template',
    domain=lambda self: self._get_mail_template_id_domain(),
    help="If set an email will be sent to the task creator when the task or issue reaches this step.")

thanks