32P-tagged fifth-instar larvae of Spodoptera litura (Fab.) and fourth-instar larvae of Spodoptera mauritia (Boisd.) were released in experimental plots, 10 by 10 m, of clover and grass respectively and traced once a day and once a night for 2 weeks by means of a Geiger counter. The clover had a patchy distribution and was mixed with grass. The dispersal pattern was not random. In the plot with S. mauritia more radiation readings were obtained in the upwind sectors. In the plots withS. litura the majority of the contacts were made in the clover, few in the grass. The results indicate that in both species the direction of the wind may have had an influence on dispersal.