From http://news.launchpad.net/cool-new-stuff/announcing-the-launchpad-plugin-api-spec

"A while ago we announced the beta versions of the Launchpad plugins for Trac and Bugzilla. These allow Launchpad to sync not just bug statuses but also comments and, eventually, whole bug reports with the remote bug trackers that have them installed, bi-directionally. The practical upshot of this is that upstream projects that don’t use Launchpad for bug tracking can install one of these plugins and never again have to worry about not seeing bugs that people file using Launchpad but don’t forward upstream.

"We in the Launchpad team realise, of course, that Bugzilla and Trac aren’t the only two bug trackers in the world. A project that uses Mantis, for example, may want its bug tracker to interact with Launchpad in the same way that Bugzilla and Trac now can. Unfortunately we can’t develop a plugin for every bug tracker out there as we don’t have the resources or the in-depth knowledge of those trackers’ internals necessary to be able to do so.

"To make it possible for anyone to develop a plugin for any bug tracker, we’ve now opened up our Plugin API spec. The spec details all the APIs that need to be implemented for Launchpad to be able to sync bi-directionally with a remote bug tracker. It’s pretty detailed, and we’ve rolled into it our experiences in developing the Bugzilla and Trac plugins so as to make sure that new plugins don’t repeat the issues that we came across when we started interacting with the first bug trackers to install those plugins."

https://help.launchpad.net/Bugs/RemoteTrackerCoverage