The larva of Epinotia nisella is best known as a feeder in female catkins of Populus, primarily P. tremuloides Michx. in North America. In Minnesota, adults were reared from larvae boring in current-growth branchlets of P. balsamifera L., with no sign of like infestation in neighboring P. tremuloides, which has thinner branchlets. The behavioral variance is explained as plasticity in feeding biology, a characteristic of insects utilizing host reproductive structures whose abundance is periodic