Two successive trials were conducted in San Cristobal to estimate economic losses caused in maize by Spodoptera. The first trial was conducted in the Fall (September/ January) and the other in the Winter (January/May). The design used was that of paired randomized plots with two treatments and five replications. One of the treatments consisted in applying monocrotophos at 0.015 each week up to the fourth week and an application of granulated Carbofuran to the foliage on the fifth week. The other treatment was the control. Ten plants per plot were counted to determine: percentage of damage and number of larvae observed. The crop in each cycle was irrigated twice. In the Fall, economic loss was 1818 kg/ha as established between the yield of the control plot and that of the plot treated with monocrotophos + 3 Carbofuran; in the Winter it was 602 kg/ha. Thus, for the first cycle, the percentage of loss was in the range of 5.8 for the treatment with insecticides and 46.8 for the control. For the second cycle the percentage of loss for treatment with insecticidas was 6.6 while the control averaged 8.2. It was found that rainfall and relative humidity play an important role and explain the differences in the two cycles.