Extensive evidence suggests that Dpp signaling controls patterning and growth in wing imaginal discs. Patches of cells undergoing excessive Dpp signaling trigger overgrowth while at the same time inducing JNK dependent apoptosis at their boundary. To investigate this process, we have developed several reporters of JNK signaling and pro-apoptotic gene expression. Using these tools, which we hope will be widely useful, we confirmed that JNK signaling is activated on both sides of the boundary. We also found that this leads to transcriptional activation of reaper, but not hid. Suppression of JNK signaling prevented reaper expression and led to a reduction in the number of apoptotic cells. Moreover, in the absence of reaper, apoptosis was no longer detected at the boundary of clones undergoing excess Dpp signaling. We conclude that morphogenetic apoptosis is mediated by JNK dependent activation of reaper transcription.