Mobile agents (MAs) have been initially developed to replace the client/server model which shows many disadvantages in WSN environments (e.g. very high bandwidth and energy utilization). Herein, we present CBID (Clone-Based Itinerary Design), a novel algorithm that calculates near-optimal routes for MAs that incrementally fuse the data as they visit the nodes while enabling a fast update of designed itineraries which is especially important for highly dynamic topologies. The order of visited nodes highly affects the quality and the overall cost of data fusion. The key MAs characteristic exploited by CBID to reduce energy consumption and response time is their cloning capability. Parallel dispatched MAs sequentially visit sensor nodes arranged in tree structures and upon visiting a node with two or more child nodes, the MAs (master MAs) clone of themselves with each clone (slave MA) visiting a tree branch. When all slave MAs return to that node, report their data to the master MA and are self-destroyed. This results in highly reduced energy consumption and response time since many MAs work in parallel. Simulation results prove the high effectiveness of CBID in data fusion tasks compared to other alternative algorithms.