Sex Attractants

Hundreds of pheromones are known with which one sex (usually the female) of an insect species attracts its mates. Many of these sex attractants or their close chemical relatives are available commercially. They have proved useful weapons against insect pests in two ways:

• Male Confusion: Distributing a sex attractant throughout an area masks the insect's own attractant and thus may prevent the sexes getting together. This "communication disruption" has been used successfully against a wide variety of important pests. For example, the sex attractant of the cotton boll weevil has reduced the need for conventional chemical insecticides by more than half in some cotton-growing areas.
• Insect Monitoring: Insect sex attractants are also valuable in monitoring pest populations. By baiting traps with the appropriate pheromone, a build-up of the pest population can be spotted early. Even if a conventional insecticide is the weapon chosen, its early use reduces
  • the amount needed
  • damage to the crop
  • cost to the grower
  • possible damage to the environment.
  Early detection of pest build-up is a key ingredient in the system known as integrated pest management (IPM).

Figure 1.1 Gypsy moth

The photo (courtesy of USDA) shows the feathery antennae of a male gypsy moth. These detect the pheromone released by the females (who do not fly). In some insects, a single molecule of sex attractant is enough to elicit a response.

Sexual Deception

• By an animal: Many species of spiders prey exclusively on moths of certain species and only on the males. Studies of one species of spider, Mastophora cornigera, show that it releases a mixture of volatile compounds that mimic the sex pheromone of the moth species it preys upon. Male moths flying upwind in search of a female end up eaten instead!
• By a plant: A number of species of orchids - each pollinated by the males of a single species of insect (wasps or bees) — emit the same pheromone that is the sex attractant by which females of the insect species attract the males for mating.