Emigration behavior was measured in the flour beetlesTribolium castaneum andT. confusum. Analysis of genetic differences among populations derived from two highly inbred lines ofT. castaneum suggests differences in the genetic bases of two important aspects of the emigration rate response curve. Significant additive genetic variance in the behavior was found in outbred laboratory populations of both species that had been subjected to cyclical variation in population density for some 30 generations. In both species, emigration behavior was significantly correlated with fecundity measured in conditioned flour, low emigration rate phenotypes exhibiting a higher fecundity.