Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a serious pest species that recently became a major threat to tomato production in the Mediterranean Basin. In Algeria, it was observed for the first time in 2008. The present study followed some biological aspects of this devastating agent in tomato greenhouses installed in the experimental station of the University of Mascara. Our results showed that sex pheromone traps were effective as T. absoluta males were trapped and their number increased during the season (from December, 2013 to July, 2014). Furthermore, dynamics of the populations seem to be closely linked to weather conditions. Captures are maximal when the temperatures vary from 20 to 25 °C and when the hygrometry is situated between 50 and 70 %. On the other hand, we demonstrated that attacks on the first floor are significantly higher than those of the intermediate and superior floors.