The demand for new insecticides is increasing due to the appearance of insect populations that are resistant to currently used products. New insecticides should be efficient in controlling pests and present low toxicity to non-target organisms. Ascia monuste (Lepidoptera: Pieridae) is a destructive pest of cole vegetables, and the fire ant Solenopsis saevissima (Hymenoptera: Formicidae) is an important predator of these caterpillars in brassica crops. Tetragonisca angustula (Hymenoptera: Apidae) is very important in pollinating many plants and providing honey. Therefore, this study evaluated the toxicity of synthetic amides to A. monuste and its selectivity in favor of S. saevissima and T. angustula. The amides (2E,4E)-N-propylhexa-2,4-dienamide (3) and (2E, 4E)-N-butylhexa-2,4-dienamide (4) caused high (96 and 93%, respectively) and fast (48 h) mortality of A. monuste. The amides 3 and 4 were not harmful to the predator (mortality of 5.7% for amide 3 and 7.14% for amide 4) and were slightly harmful to the pollinator (mortality of 38.57% for amide 3 and 28.12% for amide 4). The amides 3 and 4 are promising, as insecticides, due to the high and rapid mortality of A. monuste with low and moderate toxicity to S. saevissima and T. angustula, respectively.