Observations were made to determine the seasonal occurrence of Diaphania nitidalis (Stoll), Prodiplosis longifila (Gagne), Liriomyza huidobrensis (Blanchard), Bemisia tabaci (Gennadius), Aphis gossypii (Glover), Agrotis ipsilon (Hufn.) Spodoptera ochrea (Hampson) and their natural enemies in watermelon’s crop. located in the Agrarian University of La Molina were made the land called Field Free I of 1 ha. It was divided into five sectors in which were taken randomly 5 plants per sector, there were evaluated 25 plants in total. On each plant four outbreaks were recorded, 4 sheets randomly, as the foliage of the plant, 4 flowers and 4 fruits distributed throughout the plant, the neck of the plant and 2 meters of furrow by sector. The earth worm Agrotys ipsilon (Lepidoptera: Noctuidae) did not cause major damage. As for Diaphania nitidalis (Stoll) (Lepidoptera: Crambidae) infestation was l...