Abstract: The expression of the biotic potential of Ceratitis capitata is unquestionablyrelated on the one hand to the climatic variation and on the other hand with the quality of thelaying substrate. Moreover, its egg-laying strategy differs from a host plant to another,related to the phytochemical composition of the hosts and their period of availability. Theevaluation of these parameters based over the thermal summation “days-degree” and theperiods of egg-laying according to the phenologic stage of the plant constitute an estimatedtool of assistance in the decision making of the phytosanitary treatments. Thus, in a citrusorchard located in the Mitidja region, with 232.36°D from the first January of the study year,basing on 11.2°C temperature threshold of development, we obtained our first fly captures.Moreover, in spite of the Ceratitis capitata occurrence in the orchard, the laying begins onlystarting from certain primary metabolic host plant contents. The number of laying traces leftby the medfly in relation to the phenologic variation of some compounds on apricot fruitsindicates a positive and significant correlation between the sugar contents mean values andthe average traces of egg-laying of the species. Moreover, the number of larvae observed byfruit varieties: two varieties of peach and two varieties of fig including one early and thesecond late, showed significant differences.