Semiochemicals

What are Semiochemicals?
Semiochemicals are message carrying chemicals that are used in nature for communicating between living organisms. Pheromones are the best known group of semiochemicals.

What are Pheromones?
Pheromones are highly specific chemicals produced by many organisms including insects which elicit a response from other individuals of the same species. There are many types of pheromones but only two main types are used for monitoring and pest control.

a) Sex pheromones - these are usually produced by the female of a species in order to attract males of the same species for reproduction. This is the most common type of pheromone and is especially important for moths. Examples include Helicoverpa armigera and Plutella xylostella.

b) Aggregation pheromones - these attract both male and female insects of a species and can be produced by one or both sexes. This type of pheromone tends to be more common amongst beetles but is also important for cockroaches for example.
Other attractants are often used for monitoring. These are used either where the specific pheromone is unknown, or difficult to make, or when the alternative attractant gives superior results. These can be food based or from unrelated sources. In general these attractants are composed of foodstuffs or constituents of food which have been found to be particularly attractive to the target pest(s). Traps may also be baited with a compound or compounds which are not normally produced by an insect, nor found as a component of its food but which never the less attract the insect. Examples of this include Trimedlure used for attracting the Mediterranean Fruit Fly and Methyl Eugenol for Oriental Fruit Fly and other related species.

Pheromone Formulation
Pheromones by their very nature are very volatile and extremely unstable. To use them effectively these chemicals must be formulated so that their release into the air is controlled and so they can be protected from degradation by UV light and oxygen. A wide range of formulations have been developed with varying degrees of sophistication.
For a pheromone system to work effectively it is important to ensure that the lures are made with quality components and that the formulation has been developed to protect the pheromone from degradation and to release it at the required rate for optimal activity. It is very difficult without complex chemical analysis to determine whether any product being offered commercially is effective for the purpose. It is therefore vitally important that users obtain their pheromones from reputable sources.

Trap Designs
The lures themselves are of no use if there is not also some method of trapping the insects. Many factors influence trap design. These include the insect itself, what it does and where it occurs, the expected number of insects to be caught, the general environment of the trap, and the customer's expectation about price and longevity of the product.

Pressure Sensitive Adhesives
Pressure Sensitive Adhesives, or simply Glues, have been used for catching insects for many years. Indeed, in nature there are examples of insects being caught in natural sticky substances, such as “amber” and other plant resins millions of years ago, which are available for scientific examination to this day.
We can easily define the properties of glue that we need in order to make it an effective insect catching substance. These characteristics are its “stickiness” or “aggression”, longevity, i.e. resistance to deterioration from exposure to light, air (oxygen) dust etc, ease of application on plastic and card, health and safety properties and last but not least, economics. Combining

Mating Disruption
Many pests are the most damaging when in their juvenile stages. Most of our pest management practices, including the use of insecticides, target the damaging stages. Mating disruption, instead, targets the adults by interrupting the reproductive cycle so that no eggs or young are produced. The key to mating disruption is to use the insect’s own pheromone against it. The pheromone is formulated into high dose controlled release devices. By artificially increasing the amount of pheromone in the field much higher than what females produce, males can not find the females. Mating does not take place; eggs are not laid and the pest larvae are not produced.

Attract & Kill
Attract & Kill (or Lure and Kill) is based on the combination of a pheromone (or other attractant) and an insecticide to kill the target pest. The insects responding to the attractant contact the pheromone source and are killed or incapacitated. Since most (though not all) of the attractants available are only effective on the males, the system works by removing as large a percentage of the male population as possible thus leaving very few to mate with the females.
Often the action of the pheromone is supplemented by the addition of other attractants such as food volatiles which also attract the female. This leads to reduced egg lay and consequently fewer crop damaging larvae. This technique has been successfully applied to the control of insects such as the Olive fly, Mediterranean fruit fly, Codling moth and many other insects.