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Résumé :
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In 1995, two experiments were performed to examine the relationship between different infestation trends of Sitobion avenae and yield loss in winter wheat grown under optimal conditions in climate chambers without nitrogen or water deprivation to obtain high yield levels (experiment I: 1.9 g per ear, experiment II: 2.5 g per ear). Each trial included a comparison of the following three treatments: A) early aphid infestation under the influence of coccinellids and C) untreated control. In experiment I, the early aphid population (A) caused the same yield loss as the later undisturbed aphid population (B), while the aphid indices differed (A: 1055, B: 2307 aphid-days per tiller). The yield loss per aphid-day and tiller in treatment A (0.52 mg) was significantly higher than that in treatment B (0.30 mg). In experiment II, no significant yield loss (A: 0.01 mg B: 0.1 mg per aphid-days per tiller) could be determined despite the high cumulative aphid indices (A: 708, B: 2511 aphid-days per tiller). This phenomenon indicates enormous tolerance responses of wheat plants. The treated plants tolerated the low aphid density during the early milky ripe and the high density during the dough stage. Optimal growing conditions led to the extremely high attainable yield level, which seems to enhance the tolerance responses. The results of two experiments cannot be applied to field conditions. However, they show the enormous deviation in cereal aphid infestation - yield loss relationship. Moreover, they contribute to the understanding of physiological responses of the wheat plant to aphid infestation.
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