Counts were made of the numbers of Oscinella adults caught in water traps in plots of grass and oats and in a suction trap in north-eastern England in 1969 and 1970. The numbers of eggs laid by O. frit (L.), O. vastator (Curt.), O. nitidissima (Mg.), O. hortensis Collin and O. maura (Fall.) on their respective host-plants were also counted. In both years, there were two generations of O. nitidissima and O. nigerrima (Macq.) and one of O. maura. In 1969, there were two generations of O. frit and one of O. hortensis and O. vastator. In 1970, there were partial second generations of O. hortensis and O. vastator and a partial third generation of O. frit. O. nigerrima was the first species to appear in the spring, followed by O. frit and O. nitidissima. O. hortensis, O. vastator and O. maura emerged later, and these species dominated the trap catches in July. The proportions of O. frit and O. nitidissima increased in August, and by late September these species again dominated the catch. The proportions of O. vastator and O. hortensis in the suction-trap catches were much lower than in the water-trap catches. Adults of all species were always found in the grassland water traps before they were found in the suction trap. The migratory requirements of other species in the genus, in particular O. maura and O. vastator, may be less than those of O. frit. The oviposition period on particular grass species was relatively long, and thus control of Oscinella spp. on grassland would be difficult.