Active migration occurs through repellents and attractants. Terpenoids may act as both attractants and repellants for various insects. Glands on the labellum emit pheromones which are sexual attractants for male thynnid wasps. MCPs respond to extracellular attractants and repellents in bacteria like "E. coli" in chemotaxis regulation. Chemical attractants or pheromones may attract only a specific sex. Boric acid roach baits consist of a proprietary blend of attractants. This can include semiochemical lures such as pheromones, food attractants, host mimics, or color attractants. Proteinaceous liquid attractants in insecticide sprays is an effective method of controlling melon fly populations. These pheromones are long-range attractants and are used as male advertisements. KNF insect attractants are non-toxic methods of pest control. Cat attractants are odorants that have an effect on cat behavior. Synthetic attractants like methyl eugenol are very effective with tephritid flies. For large trapping efforts, additional traps are generally cheaper than expensive artificial attractants. Parrot cichlids fed with natural colorants and attractants naturally develop a red color. Signalling odours in reproduction are called attractants; their function is to bring about successful mating.