When expression is driven by Scer\GAL4^btl.PS, ectopic fusions occur between adjacent dorsal branches and terminal branching is repressed. The cells involved in the ectopic fusions become tightly attached by an intercellular junction. Terminal branches arising from the dorsal branches are stunted and those arising from primary branches are fewer than wild type and stunted. Sporadically (and more often when expression is driven by Scer\GAL4^tracheal), dorsal branches and ganglionic branches extend ectopic terminal branches. The number of tracheal cells is not affected nor is primary branching. Cell markers indicate a transformation of presumptive terminal or antifusion cells into fusion cells.