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Two Algerian populations of Heterodera avenae originating from Cued Smar in a sub-humid coastal plain and from Tiaret in an inland semi-arid plain were subjected to different temperature treatments and juvenile emergence evaluated. These populations were compared with two populations, Fr1 and Fr4 from southern and northen France, respectively, which represent two ecotypes with respect to hatching cycles in response to temperature. The two Algerian populations hatched over a wide range of constant temperatures (3 to 25 degreesC) but differed in the times at which juveniles emerged from the cysts. Simulation of seasonal temperature variations (from summer to autumn or winter and, conversely, from winter to spring or summer) demonstrated diapause in these two populations, induced by higher temperature (20 and 25 degreesC) treatments and broken subsequently by lower temperatures (3 and 7 degreesC). Both Algerian populations of H. avenae represent the Mediterranean ecotype, with biological variations that may represent regional adaptations to more or less severe climatic conditions.