Tritrophic associations (plant-aphid-natural enemy) were utilized as model examples or approaches to elucidate the occurrence and adaptations of invasive exotic species in native ecosystems (agro-ecosystems) (in the Czech Republic). Three groups of cases/models were distinguished: 1. Invasive exotic plant and adapted native phytophagous/ entomophagous insects, or simultaneous or subsequent infestation by exotic (invasive) species; both cases even often occurring together. Model: Impatiens parviflora, I. glandulifera vs. Aphis fabae Scop. (Native), Impatientinum asiaticum Nevsky (exotic), and native parasitoids, predators, and pollinators. 2. Invasive exotic species attacking native plants. Model: Macrosiphum albifrons Essig (North American) vs. Lupinus spp. Model: Aphis spiraephaga Müll. (Expansion from C.Asia) vs. Spiraea spp.ornamentals, and natural enemies. Model: Diuraphis noxia (Kurdj.), expansion from C. Asia over the Mediterranean to the south-eastern and central Europe, on cereals, and native and introduced natural enemies. 3. Biological control agents. Established exotic parasitoids spread from the original release sites and act as expansive species in the new environment.