Due to the lack of centralized coordination and time-varying network topologies, designing an efficient query processing scheme is admittedly challenging in mobile ad hoc networks (MANETs). Each node often broadcasts a query, retrieves its queried data item, and periodically checks its freshness but a non-negligible communication overhead may incur. In tight of this, we propose a set of query processing strategies by deploying a validity region to efficiently minimis the query traffic and update the freshness of the queried data. We first investigate simple rectangle and convex hull based validity regions and their corresponding query processing schemes, and then extend them by adaptively combining both techniques and considering an opportunistic overhearing. We conduct extensive simulation experiments using the OMNYT++ simulation package for performance comparison and analysis, in which an infrastructure-based query processing approach is also adjusted to be implemented in MANETs. The simulation results indicate that our convex hull based adaptive query processing approaches can reduce the number of queries but it increases the time spent in the validity region.