In this study a record and an evaluation of the Spodoptera larvae complex (Lepidoptera: Noctuidae) of commercial transgenic cotton (Cry1Ac) planted in the central area of Tolima, Colombia were registered. During three plant developmental stages: vegetative, reproductive and maturity, 83 commercial plots with areas ranging from 1 to 10 hectares, were evaluated. Spodoptera complex (Spodoptera frugiperda, S. ornithogalli y S. sunia) activity was evaluated in 315 ha, sampling seven plants per hectare, including refuges (12,6 ha), taking into account three different larvae sizes, small &lt; 0.5 cm, medium &gt; 0.5 and &lt; 1.5 cm and large &gt; 1.5 cm, as well as their location in the plant (leaf, flower and structure). There were statistically significant relationships between the larvae incidence (percentage of cotton plants with Spodoptera larvae present) and the different cotton genetic materials, with a significant higher larvae incidence in the transgenic plants (11,98% SE 4,03) than in conventional plants (9,13% SE 3.08) (0,0021*). This tendency was also observed among Spodoptera complex species, both genetic materials and the three plant developmental stages. S. frugiperda prevailed in flowers and capsules, S. ornithogalli in leaves and flowers; and S. sunia in leaves. This pattern was observed in both genetic materials with statistical significance (0.0001*). Larvae of all sizes were recorded in plants of both genetic materials; although there was no statistically significative dependency. Finally, there were small, medium and large S. frugiperda larvae in flowers and capsules, structures where the Bt toxin expression is the lowest in the plant.