The efficient control of insects has long presented man with a vexatious problem, particularly with respect to insects which compete with man for food supplies and other vegetable material or contribute to the spread of disease. The twin concerns of world wide hunger and recent awareness of environmental and health effects from the use of chemical insecticides has further compounded this ancient problem.
With the realization that many of the chemicals which have been used to control insects are toxic not only to the insects themselves but to man as well, attention has been focused on other means of effecting control of insects which do not possess environmentally objectionable characterics.
One area of recent interest has been the isolation, extraction or synthesis of substances which are secreted by insects of one sex to attract the insect of the opposite sex. Combined with suitable means for either traping and destroying the insects or interfering with their reproductive cycle, these substances offer a future hope of controlling insect populations in an environmentally acceptable manner.
Unfortunately, although the substances secreted as sex pheromones by various insects can be identified, obtaining them is useful quantities has proven difficult. The amount of attractant actually secreted by the insect is extremely small--in the order of nanograms--thereby effectively precluding the insects themselves as a natural sources for the material. In addition, synthetic means for isolating insect sex pheromones have proven to be difficult and expensive.
Naturally occuring insect sex pheromones are known to possess generally a common molecular structure of a linear chain of carbon atoms with one or more double bonds and a remote functional group such as an acetate ester or aldehyde. These compounds can take several isomeric forms and it is recognized that the relative proportions of the respective geometric isomers are critical to their function as insect sex pheromones.
Unfortunately the preparation of the individual isomers chemically or their separation from a mixture has heretofore been both difficult and expensive, thereby effectively precluding production of these pheromones synthetically at attractive cost and in suitable quantities for commercial use.
While the prior art has suggested the formation of inclusion complexes as a means for carrying out some chemical separations of organic compounds, it has not previously been recognized or suggested that synthetic insect sex pheromones could effectively be isolated in this manner. More specifically and with particular regard to compounds having the structural characteristics of insect sex pheromones there has not been a recognition of a structural relationship between the dimensions of the inclusion complex and the size and position of functional groups which relationship would permit separation of the geometric isomers.
Examples of prior work in this area generally are as follows: