Put simply, pheromones are chemical messages between individuals of a species. They developed early in the history of life and are used by all sorts of animals, but they are particularly important to insects. With a few exceptions, pheromones are all made from the same simple chemicals with finely tuned differences in the mix creating different messages. Using this system, insects can convey all sorts of messages. The main types of pheromones used by insects are:
Sex Pheromones – Used to attract a mate
Alarm Pheromones—Used to warn of danger
Aggregation Pheromones—Used to attract other members of the species
Marking Pheromones—Marking the spot were eggs were laid
Trail Pheromones—Making a trail for others to follow
What are Pheromones Made Of?
Insects create pheromones from substances readily available in their environment. One fascinating example is found in a tropical bee that must collect pheromone material from certain species of flowers. Without the flower, there can be no sex. Since this flower is an important source of pollen, it doesn’t make sense to mate when the flower isn’t available, so the plan usually works out for the best.
Some of the alarm pheromones in bees and ants are derived from chemicals used in defense. These insects are used to having defense chemicals in the air when they are under attack, so it’s easy to see how they developed the use of the same chemicals to signal alarm.
The North American tiger caterpillar uses defensive poisons it gets from its host plant, the milkweed, and males store part of this poison to use as a pheromone. Females choose the male with the strongest pheromone, knowing that he will pass his poison to her when they mate. This makes her better able to defend her eggs.
Sending, Receiving, and Responding to Pheromone Messages
Insects receive pheromone messages with their antennae. These antennae have tiny sensory hairs on them which can receive messages at amazing distances. When a message is received, the recipient responds immediately.
When a male moth, for instance, picks up a sex message from a female, he will immediately fly straight toward the source of the pheromone. He may lose the message from time to time in his flight, and when he does he will fly in a zigzag pattern until he picks it up again.
Social insects such as bees and ants that organize themselves into colonies use another type of pheromone to keep the colony in order. An insect passes on this type of pheromone by tapping the recipient with his antennae where the pheromone is stored.
Pheromones control a vast array of activities and individual recognition in social insects. They can help the insect determine age, sex and social status of the insects he meets, and they also control complex activities such as foraging and nest building.
Using an Insect’s Pheromones Against Him
There are all sorts of deceptions in the insect world. Predators and parasites have learned to detect messages that were intended for other antennae, and use them to locate prey. They can also make counterfeit messages to attract their prey.
Flowers get into the act, too. Some orchids need certain types of bees or wasps for pollination. These orchids have evolved to resemble the insect in appearance and smell, and produce a pheromone chemically identical to that of the insect they are trying to attract. Bees that are fooled into trying to mate with the flower pick up pollen that is passed on to the next impostor.
Humans also use pheromone trickery to control insects. We use pheromone bated traps to control pest insects without harming the environment or other insects. This method has been used successfully against a number of destructive agricultural pests.
References:
“Firefly Encyclopedia of Insects and Spiders”; Christopher O’Toole; 2002
“Encyclopedia of Insects”; Vincent H. Resh et al.; 2009
“Smithsonian Handbooks: Insects”; George C. McGavin; 2002
