Pheromones
by Rudy Scheibner
(from: University of Kentucky YouthFacts. Youthfacts are designed for teachers, 4-H'ers, and anyone else who wants to pursue an interest in Entomology. Several articles give resources and basic information about insects and their relatives, while others outline activities with different insect themes. Feel free to copy and distribute the Youthfacts, but please give credit to the authors and the University of Kentucky Entomology Department.)
Although many kinds of insects can communicate with each other with sound signals (For example, cricket chirps), or with visual signals (For example, bee dances); perhaps the most common means of insect communication is with pheromones. A pheromone is a chemical produced by an insect to send signals or messages to other insects of the same species. Many of the insect pheromones are volatile chemicals, that is, evaporate easily and fill the air where they can be de- tected by smell by other insects quite far away. Other pheromones may not be so volatile and are detected by tasting. One of the most common pheromone messages is the odor sent by a female to let males know where she is and that she is ready to be mated. Pheromones used to attract mates are called sex phero mones.
Chemists have been able to make the sex pheromones of many kinds of pest insects; and entomologists have been experimenting with ways to use these sex pheromones to control the pests.
One way of using sex pheromones for insect control is by mass trapping. A lot of traps are set out to catch most of the males before they can fertilize the females. Unfertilized females will only lay sterile eggs that won't hatch. Another method is the confusion technique. A general area is sprayed with the pheromone to confuse the males that are trying to find a mate. Both these methods are expensive and therefore not usually practical. However, just a few traps are enough to tell when the mating season of the insect occurs. With that information insecticide sprays can be timed for maximum effectiveness.
Entomologists at the University of Kentucky are now experimenting with a control technique of attracting tobacco budworm moths to a trap that doesn't hold them. (Sounds pointless. Doesn't it?) The trap looks like an upside down ice cream cone with the tip cut off. Male moths are attracted by a sex pheromone to the bottom of the trap, and when they leave they tend to move upward in the cone to escape through the hole in the top. The path to their escape is dusted with a virus powder that gets on the moths' bodies. When the dusted males mate, some of the dust gets on the females. When the females lay their eggs, some of the dust gets on the plant around the eggs. When the caterpillars emerge and begin to eat the leaf, they also swallow some of the virus laden dust. The virus causes a disease that kills the budworm caterpillar. The virus does not harm the plant or insects that may be beneficial predators or parasites of budworms. The advantages of this technique are that is takes very little of the killing agent, it is placed exactly where the pest is trying to do its damage, and the killing agent is harmless to beneficial insects that may come in contact with it. The pest is also less apt to develop resistance to the virus, like so often happens with manufactured insecticides.