Insects use many different semiochemicals, chemicals that convey messages between organisms. (The Greek word "semeio" means sign.) Although semiochemicals may seem analogous to tastes or smells perceived by humans, the use of such compounds by insects is characterized by a high degree of sensitivity and specificity. |
Receptor systems that ignore or screen out countless irrelevant chemical messages are nonetheless able to detect messenger compounds at extremely low concentrations. Detection of a chemical message triggers very specific unlearned behaviors or developmental processes.
Chemicals that act as attractants or carry other messages across distances are volatile (quick to evaporate) compounds. When released into the air, they can be detected by certain insects (those receptive to a specific compound) a few inches to hundreds of yards away. Chemicals that carry messages over considerable distances are most often used in pest management.
Many chemical and visual lures attract insects and can be used to monitor or directly reduce insect populations. Because these attractants are used in ways that do not injure other animals or humans or result in residues on foods or feeds, they can be used in an environmentally sound manner in pest management programs.
The effective use of attractants and traps requires knowledge of basic biological principles and the pest- or crop-specific details involved in individual applications. This publication presents background information and specific guidance on the use of attractants and traps for monitoring and directly controlling insect pests. Its purpose is to aid farmers, homeowners, and others in understanding and making appropriate use of available technology. It covers chemical attractants, visual lures (such as light), and attractant-baited and unbaited traps.
Allelochemicals are semiochemicals that affect one or more species other than the producer. Of known allelochemicals, volatile compounds similar to those given off by food sources (plants or animals) are important in pest managements. Feeding attractants are examples of kairomones, allelochemicals produced by one species but used to advantage by another species. For example, carbon dioxide given off by humans and other animals is used as a kairomone by female mosquitoes seeking a blood meal. In contrast, allomones are allelochemicals that favor the producer. For example, secretions that deter predators are allomones.
Although terms such as pheromone or kairomone help describe the functions of message-carrying chemicals, these words often oversimplify the complexity of chemical communication. A single chemical signal may act as both a pheromone and a kairomone; for example, the compounds emitted by a bark beetle colonizing a host tree attract other bark beetles (functioning as an aggregation pheromone), but the same compounds also attract certain predators and parasites that attack these bark beetles (functioning as a feeding attractant or kairomone).
Practical use of pheromones or feeding attractants for pest management usually requires that specific active chemicals be isolated, identified, and produced synthetically. The synthetic attractants--usually copies of sex or aggregation pheromones or feeding attractants--are used in one of four ways: (1) as a lure in traps used to monitor pest populations; (2) as a lure in traps designed to "trap out" a pest population; (3) as a broadcast signal intended to disrupt insect mating; or (4) as an attractant in a bait containing an insecticide.
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