Microplots (30x30x50 cm) were inoculated at Bari with 0, 0.125, 0.25, 0.5, 1,2,4,8, 16, 32 and 64 eggs of Hete rode ra avenae Woll.lg soil and sown with hard wheat in 1984 and again in 1985, to investigate the relationship between population density of the nematode and yield of wheat. Some of the microplots were used in 1985-1986 to investigate the decline of H. avenae populations and the hatching of the nematode throughout the year, under southern Italian climatic conditions. The nematode affected the yield in 1985 when a tolerance limit of wheat to the cereal cyst nematode of 1 egg/g soil and minimum relative yield of 0.60 and 0.65 for weight of grain and above ground parts of the plant were estimated. Apparently no damage was caused by the nematode in 1986. Maximum reproduction rates of H. avenae of 5.6 and 3.4 and equilibrium densities of 40 and 36 eggs/g soil were obtained in 1985 and 1986, respectively. In the absence of a host, populations did not decline during summer but then by about 40% between September and November and by about 90% between September and March. Almost no eggs hatched in late spring and in summer, but about 50% of the eggs hatched from the second half of October through to March.
