Wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) stems in the Negev Desert of southern Israel are subject to mass infestations by stem sawflies larvae, primarily Trachelus tabidus F. (Cephidae, Hymenoptera). Infestations up to 55% and 50% in wheat and barley, respectively, were found in 1982/83. In addition, up to 8.6% of wild oat (Avena sp.) stems were cut by sawfly larvae in June 1983. The phenology of the insects was studied in 1981 to 1983 using yellow watertraps to catch adults and by dissecting infested stems to establish the pre-imaginal stages. Adults emerged at the end of February at Magen and at the beginning of March at Gilat. Eggs and newly emerged larvae appeared in April. Larvae in diapause were found in cut stubs at the end of April and beginning of May. Pupae were found at the end of January and February. Of the sawfly specimens trapped in 1982 and 1983, the great majority was identified as T. tabidus and less than 5% as Cephus pygmaeus (Cephidae, Hymenoptera). The males of the sawflies appeared 4-6 days before the females, and were less numerous than them. About 12% of the larvae were parasitised by Tetrastichus sp. (Chalcidoidea, Eulophidae) in wheat, barley and wild oat, and about 4% by Collyria sp. (Ichneumoidea, Ichneumonidae) in wheat and barley stubs.