Pest control pheromones

In an article dealing with applications of olefin CM to a series of commercial products [138], solvent-free CM between ( )-3-hexene (produced by homocoupling of 1-butene) and 11-eicosenyl acetate 303 (produced from jojoba oil) was used to produce acetate 304 (Scheme 59), which is - as a natural 82 18 (EIZ) mixture - the pheromone of omnivorous leafroller, and serves as an environment-friendly pest controlling agent. The CM reaction was performed without solvent at 5 °C with a 4 1 mixture of ( )-3-hexene and 303, in the presence of only 0.2 mol% catalyst C, and furnished after 20 h coupling product 304 ( Z=83 17) in 50% yield. 

Behavioral and Hormonal Chemicals. Sex pheromones, which attract pests to traps, are used effectively to control some insect pests, like the grape berry moth (46) and cabbage looper. With other Insect pests, sex pheromones have been effectively used to monitor the size of pest insect populations to determine when pesticide treatments should be made. 

The purpose of synthesis in pheromone science is (1) to establish the proposed structure including absolute configuration and (2) to provide samples in amounts sufficient for biological studies and practical pest control. 

The synthesis of pheromones remains an important cornerstone of pheromone research and development. The initial synthesis of an insect pheromone serves not only to confirm the structural identification, but also provides authentic material for either laboratory or field bioassay. Oftentimes, larger quantities of the pheromones are desired for the development of monitoring and pest control methods. The scale up of the synthesis of complex pheromone compounds is often a major bottleneck in the practical application of pheromones. Also, the unusual structure of some pheromone compounds beckons synthetic chemists to apply new methodology in order to show off their methods. 

Rice, E. L. "Pest Control with Nature s Chemicals Allelochemicals and Pheromones in Gardening and Agriculture" University of Oklahoma Press Norman, 1983. 

Pheromones are classified in at least ten different categories. The most conq)lex category involves enantiomers at a specific composition (Mori 2000), implying multiple receptors. Other complex networks of biological events involve terpenoids released by plants in response to grazing by herbivores. These metabolites can be used to attract parasitic wasps for pest control (Tumlinson 1993), or, like the strigolactones (Table 12.1), as useful germination stimulants of root parasites of plants in the families Scrophulariaceae and Orobanchaceae (Welzel 1999 Ryan 2001). 

There is hope that insect sex lures can be used to disrupt the mating pattern of insects and thereby control insect population. This approach to pest control has important advantages over conventional insecticides in that the chemical lures are specific for a particular species also they are effective in remarkably low concentrations and are relatively nontoxic. There are problems, however, not the least of which is the isolation and identification of the sex attractant that is produced by the insects only in minute quantities. Also, synergistic effects are known to operate in several insect species such that not one but several pheromones act in concert to attract the opposite sex. Two notable pests, the European corn borer and the red-banded leaf roller, both use cis-11-tetradecenyl ethanoate, 32, as the primary sex attractant, but the pure cis isomer is ineffective unless a small amount of trans isomer also is present. The optimum amount appears to be between 4% and 7% of the trans isomer. 

Sex pheromones, chemicals that attract one sex of an insect to the other, also have uses in pest control. They are often utilized with traps to monitor the number of pest insects in an area, and when applied in the field at higher levels, they can disrupt reproduction or egg laying. 

Pheromones as Pest Control Agents A Brave New World... 

As indicated earlier H. subflexa has recently become the subject of numerous pest control studies due to the potential for population control of H. virescens by a sterile hybrid release program. However, these two species maintain reproductive isolation despite broadly overlapping ranges and intersecting reproductive periods. Hence, barriers to interspecific gene flow are most likely due to differences in their respective sex pheromone communication systems and, as indicated earlier, there are considerable differences in the pheromone gland contents of each. 

Considerable progress has been made over the past decade in the application of insect sex pheromones to pest control programs. As the commercial applications of pheromones have expanded, the demand for larger quantities of certain of these compounds has increased, but many of the published syntheses cannot readily be carried out on a kilogram scale. 

Persoons, C.J. "Structure elucidation of some insect pheromones a contribution to the development of selective pest control agents" Thesis, Wageningen, 1977. 

The potential rewards of this approach have, in the past several years, prompted a number of companies to undertake the development of a commercial technology for applying the pheromone disruptant, thereby hastening the day when this important technique can be fully exploited as a safer and more efficient means of pest control. 

Those who have followed the pheromone field know that there have been great strides forward in virtually every aspect of pheromone technology, especially in the past decade. Aside from the biological aspects of the problem, which are not directly addressed here, substantial progress has been made in isolation, identification, analysis and synthesis of pheromones, and—most important and recently—in actual applications of insect pheromones to solve difficult pest-control problems. 

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