ON THE POPULATION-DYNAMICS OF HYALOPTERUS -PRUNI GEOFF (HOM, APHIDIDAE) IN TUNIS

In the Tunis area, the assessment of infestation levels by Hyalopterus pruni Geoffroy on almond trees was established by considering only th e proportions of colonies with more than 100 individuals per leaf. Hig h, medium and low infestation levels were recorded during three years, 1992, 1993 and 1994, respectively. However, host infestation often st arted in mid-February, reached a peak at the beginning of April and th en declined and disappeared by the end of May. The responsible factors of this decline related to: 1) the gradual decreasing fecundity of ap terae; and 2) alatae migration. On the other hand, the fundatrix larva e survival and reproductive potential expression of apterae were mainl y influenced by the phenology and vigour of host plant. On peach tree, infestation was later (beginning of May) but could continue to the en d of summer. The decline of population could be associated with premat ure leaf fall. Except for this, the combined effect of migration and n atural enemies were allowed to maintain aphid population at acceptable level. Among abiotic factors very high summer temperatures (>43 degre es C) led to total aphid mortality. The regulatory action of these fac tors has been analysed and discussed.