All insects generally have one pair of antenna on its head and working as sensory organ. With the help of antennae, they can detect the odour, humidity, temperature, sound, way and food; find an opposite sex individual, communication to each other etc. You must have seen that when ants passed in rows, they can touch their head one to another and exchange the messages. Our pheromone technology may not be work, if antennae are absent on insects.