The shoot apex in plants contains stem cells that give rise to the aerial parts of the plant such as leaves, shoots, and flowers. When larvae of the specialist insect, Gypsonoma haimbachiana (Kearfott), feed on elongating cottonwood (Populus deltoides Bartr.) shoots beneath the shoot apex, the fate of buds above the feeding site is changed from leaf/shoot to floral. A signal either produced by the larva, or by the plant in response to larval feeding, might be altering the genetic program(s) in the shoot apex. This interaction between Gypsonoma and cottonwood may provide insights that could help us understand flower bud initiation in woody perennials at the molecular and chemical levels. Understanding how Gypsonoma larvae stimulate more floral bud formation in place of leaf/shoot buds can potentially be used to manipulate seed/fruit production and delay or hasten the onset of flowering.