Three weekly applications of 5.0 kg of rubidium chloride (RbCl)/ha to corn plants beginning when the plants were at 1st tassel were superior to a single application of 10 kg/ha made when silks began to dry for labeling the corn earworm,Heliothis zea(Boddie), with Rb. The Rb contents of larvae and moths from the former treatment did not overlap with those of insects from untreated plots. Fall armyworms,Spodoptera frugiperda(J. E. Smith), on corn were also labeled using the RbCl sprays.In a study on dispersal of corn earworm moths from a corn field labeled with Rb, male moths were collected in traps baited with virgin females in 4 cotton fields 0.5–2.8 km from the treated corn.