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Pheromone traps of different firms for control of harmful insects |
Odorant substances secreted by animals that serve for chemical effect on other animals of their species are termed pheromones. The study of pheromone communication in animals is a part of science of their behavior. Pheromone communication is a relatively broad notion. Including also a more widely used, but narrower term chemorecepy. Pheromone communication is at the same time an object of (at least) two areas of study, i.e etology and chemical ecology. Communication by means of pheromones is usually regarded as a complex system including mechanisms of pheromone biosynthesis, pheromone release into the environment, dispersal in the environment, perception by other individuals and analysis of signals obtained. The study of pheromone communication of beetles is of particular importance for the development of ecologically clean ways of control noxious species. A practical result of study on pheromones of beetles is the creation of efficient traps for a number of pests (primarily for click beetles, bark beetles and dermestids (bakon beetles)).
Pheromones are used by beetles and other insects for most different purposes. In the manual "Pheromones" (Skirkyavichyus, 1988) 30 types of pheromones have been specified, each having a particular purpose. The most important for beetles and particularly well studied ones are sex pheromones (or sex attractants) that serve to facilitate meeting of males and females. The manual mentioned contains information on pheromones of 172 species of beetles. In 144 cases theses are sex pheromones. Normally sex attractant is released by females, but in beetles cases when they were released by individuals of both sexes are known. Efficiency of this type of pheromones is sometimes very high and the amount of substance released by one female is sufficient for attracting thousands of males. Accordingly the distance at which this substance acts may under favorable conditions attain several kilometers. Therefore man tries to use sex attractants primarily for disorientation of males of noxious beetles in nature and for catching them in pheromome traps. In both cases percentage of fertilized females delines and as a result abundance of pest decreases. The most promising results were obtained in control of click beetles, bark beetles, dermestids (bakon beetles) chafers and true weevils. Sex pheromones are used also for revealing pests at their low abundance and for the assessment of the level abundance when it becomes high.
The second widely spread and studied are aggregation pheromones of beetles (52 species according to the data of the above manual), which help individuals of the same species to form aggregations necessary for successful feeding and wintering. In some cases this type of pheromones may substitute for the sex pheromone, because in aggregations of beetles encounter of sexes for coupling is facilitated. Aggregation pheromones are of particular importance for bark beetles when they attack a healthy or insufficiently weakened coniferous tree. Single attempts to penetrate into such a trunk terminated with death of female in the releasing tar and do not cause any harm to the tree. Only massed attack of one tree has biological sense for bark beetles: a part of females dies, but the tree is quickly weakened and penetration of other participants of attack beneath the bark is successful. Aggregation pheromones are also used in traps and help reduce abundance of noxious species.
Of other known types of pheromones in beetles most completely studied are marker pheromones (for 5 species in the manual by A. Skirkyavichyus) which serve to mark presence in an area of food substratum and therefore prevent laying of eggs by different individuals, and therefore possible overpopulation of substratum by larvae in the future. Probably beetles have trace pheromones, which are used most frequently in search for nes or burrow. These substances remain on the surface in the form of marks or air is saturated by them.
There are interesting methods for providing species specificity of pheromones. Pheromone always comprises several chemical substances. These are normally organic compounds with low molecular weight, i.e. from 100 to 300. Species differences of their mixtures are attained by one of three methods: 1) similar set of substances with their different ratio in each species; 2) one or serveral common substances, but different additional substances in each species; 3) totally different substances in each species.
The knowledge and practical importance of pheromones in different families of beetles is convincingly shown by results of calculation of the number of species for each family in the manual "Pheromones" (Skirkyavichyus, 1988), including data for 172 species (families for which several species have been listed are only mentioned).
Using of synthetic pheromones is one of the most ecologially safe methods of control of noxious beetles. Chemical substances that form a part of them are not poisonous and are used in minor quantities that cannot affect humans and the enivironment. The most important thing is that pheromones are species specific and affect only the needed species having no effect on other animals.
A.L. Lobanov, November 2001
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