Chromolaena odorata (L.) King and Robinson is a native of the neotropical region and has become a serious invasive weed in the humid tropical Africa, Asia, and Micronesian Islands including Guam. A successful culture of the chromolaena stem galling fly, Cecidochares connexa Macquart (Diptera: Tephritidae) received from Colombia via Indonesia, was established and maintained at the University of Guam’s Western Pacific Biocontrol Quarantine Laboratory (WPBQL). After host specificity testing and confirming that it is specific to C. odorata, the fly was field released in 2003. Since its introduction in the field, C. connexa has spread extensively throughout the island. Initially, the spread of C. connexa was slow. It took one year before the fly had dispersed one kilometer downwind and half a kilometer upwind from the initial release point. Six months later, it had spread two kilometers downwind. In the second year, however, C. connexa was found to have spread over 10 kilometers downwind and two kilometers upwind from the release point. At present, the C. connexa galls have become evident on chromolaena throughout the island. The chromolaena gall fly is considered an effective biological control agent, because it induces galls both on the terminal and axillary vegetative meristems. The galls act as nutrient sinks contributing to reduced vegetative growth and the overall height of the plant. Galling also reduced number of flowers and seeds produced.