Pheromones are chemicals used for communication between individuals of a given species.
Female insects often release a very specific odor (pheromone), which will be detected by males at often long distances. In this way the males will be able to locate the female by flying upwind while following the odor plume.
For some insect species, these very specific pheromones have been identified and can now be synthesized. These synthetic pheromones can then be used as a tool in pest management.
One way to use pheromones is to use them as bait in traps. Unfortunately, it is usually not possible to control a pest population with these traps as they only catch the male insects. But pheromone traps can be useful to monitor the pest population. High catches of males will tell the farmer that the population in his field is increasing and that female moths are ready to lay eggs.
Another possible way to use pheromones is for mating disruption. By releasing a lot of pheromone in the field, the whole air will be saturated with these odors. Consequently, the male insects will not be able to locate the female insects and mating will be disrupted. However, this technique is still being developed and at this moment very expensive.