it is not just the developer OR the Tester is responsible for integration testing, Both of them are equally responsible according to their responsibilities. The developer who writes the code is responsible for performing the integration of modules w.r.t. code ( should be understood as part White Box Testing ) Then after checking the modules for their integration it will be passed on to the Q.A. team, Here it will be the responsibility of the Q.A. team to check the integration b/w the modules according to the requirement specifications.
Don't worry about integration testing but u need to have idea about tht basically integration testing is done by white box test engg (developers )but as a black box test engg u need to have that idea .
Integration Tester(Integration QA Analyst) is responsible for the Integration. Its up to the role of the tester. But in our concern for Integration QA Analyst is the responsible person.