• Pheromones
• Chemical Communication
• Allelochemicals
• Allelopathy

Pheromones

Pheromones are behavior or development mediating semiochemicals which organisms use to transmit information between individuals of the same species. They include sex attractants, aggregation and alarm signals, trail or territory markers, oviposition deterrents or compounds which induce gamete release or control more complex social behavior, and govern many other activities. Most of these species-specific messages are coded in complex multicomponent mixtures released in extremely small amounts.

Chemical Communication

Chemical communication among insects is often elaborate and multifaced. Knowledge of the function of these systems and of the molecular structures of the chemicals involved provides the basis of highly selective techniques of pest control. Modern methods in integrated plant protection and forest pest management employ synthetic insect semiochemicals in various ways.

Monitoring

Traps baited with synthetic pheromones are used to monitor the build-up of infestations, to optimize the timing of other operations in pest control, and to check the efficiency of these control methods.

Mass trapping

Population densities may be kept below the economic damage threshold by mass trapping with attractive baits.

Disruption

Mate-finding may be disrupted by deploying overdoses of female sex pheromones to cause disorientation of the males.

Repulsion

Deterrents which signal "keep away" may be used to repel insect pests.

Allelochemicals

Allelochemicals play important roles in interspecific communication. They constitute signals in predator-prey relations, host-parasite and herbivore-plant interactions, and may be responsible for attraction as well as chemical defense. Recognition, location, and selection of prey. hosts, or habitats as well as pollination behavior are strongly influenced by both volatile and nonvolatile compounds.

Herbivores may derive benefits not only from the energy content of their food but also by exploitation of secondary metabolites which the plant contains. Direct responses of plants to attack by herbivores or to infection by microorganisms include biochemical reactions, such as the production of defensive "phytoalexins", and changes in the production of other secondary plant constituents. Under insect attack, plants may produce signals which attract insect predators providing a mutual benefit at two different levels. Volatile compounds have been identified which are released by damaged plants and which induce defense mechanisms in other nearby individuals.

Allelopathy

Allelopathy involves chemical interactions at all levels of complexity, from microorganisms to higher plants, and is inextricably interwoven into ecological phenomena. In this context, competition for food and living space is often carried out chemically: all sorts of antibiotics; toxins; germination- and growth-inhibitors or stimulants may be released for these purposes. Adsorbed by the surrounding soil or upon direct action through the air, allelochemicals are used by plants and microorganisms to manipulate partners, competitors, and ecosystems. Knowledge of the chemistry and biology of allelochemicals provides many opportunities for practical application in biological control methods.

Chemical communication for the peaceable exchange of information as well as for chemical aggression and defense is by no means restricted to the terrestrial world: pheromones and allelochemicals are well known from fish, marine invertebrates, and algae. The co-existence of immobile organisms such as corals or sponges in complex communities is to a large extent chemically mediated, their defense systems being made up of highly active allelochemicals. Some of these compounds exhibit exciting physiological properties which are of high medical and agrichemical interest. Mechanisms of adaptation, including tolerance and symbiosis, feeding preferences, and chemical mimicry are all among the basic aspects of coevolution which are currently subjects of detailed study.