Semiochemicals approach

Because the chemical signals (semiochemicals) are normally produced in minute amounts and diluted in the environment with a complex mixture of chemical compounds derived from a myriad of sources, the olfactory system in insects evolved as a remarkably selective and sensitive system, which approaches the theoretical limit for a detector. For example, it has been estimated that the male silkworm moth is able to distinguish within 1 s 170 nerve impulses generated by the female silkworm moth s sex pheromone from 1700 spontaneous nervous impulses [ 1 ], thus, operating on a remarkably low S/N ratio ... 

Techniques in isolation and structure elucidation of (volatile) semiochemicals from beetles are the same as in other insects. Problems are mainly due to the often very small amounts of target compounds, embedded in large amounts of non-active substances which form a kind of cosmetic formulation for the biologically active principle. Comprehensive reviews of analytical approaches have been published [18-20]. 

On a more positive note, the concerted attempts of scientists over the past few decades to unravel the semiochemical communication of mice and especially the work on the MUPs of these animals, could well serve as an excellent example of how this type of research should be approached and of the benefits that can be reaped from interdisciplinary collaboration. 

The use of single semiochemicals in the field is not usually sufficient for pest control, but by combining semi-ocheinicals, substantial protection can be achieved using an integrated approach called the push-pull system. The push is located in the crop and may comprise antifeedants, nonhost semiochemicals, attraction of predators or parasitoids, oviposition deterrents, or epideictic pheromones. The pull component comprises lures or trap areas away from the crop containing the sex pheromone, host odors, oviposition... 

While many molecular genetic approaches to studying COBP proteins were reported, little has been achieved by chemistry-based studies. Current theories propose that these proteins bind either a wide range of semiochemicals... 

Winston, M. L., 1992, Semiochemicals and insect sociality, in Insect Chemical Ecology. An Evolutionary Approach, B. D. Roilberg,ed., Chapman and Hall, New York, pp. 315-333. 

A valuable approach is to use the instantaneous physiological response of a mammal to individual components separated from a semiochemical substrate to indicate which may be worthy of detailed behavioural study. Instantaneous heart rate changes have been monitored telemetric-ally in rabbits constrained to monitor continuously the effluent from a gas chromatographic column on which rabbit scent components are being separated (Goodrich et al., 1981). It is quite possible, however, that components which do not elicit such a response could have an important semiochemical role. 

A complementary approach to such response-guided strategies is to examine as far as possible the entire "chemical image" which one mammal presents to another, paying particular attention to those features which vary with important biological parameters, for these contain information which the species could exploit semiochemically. An emphasis on the patterns of occurrence of compounds associated with a semiochemical substrate would also accord with the view of Beauchamp et al. (1976), that mammalian chemical signals are more likely to be encoded in the patterns of occurrence of compounds rather than in individual biologically active substances. 

A further problem with most test regimes is the limited number of behavioural responses which can normally be measured and compared with the wide behavioural repertoire exhibited in the natural environment. In our present work at Bristol we are making a detailed inventory of the behaviour patterns exhibited by a small herd of cattle at pasture to determine in detail the change in behaviour pattern which accompanies the approach of estrus. This information can then be used to assess the semiochemical significance of various biological materials. 

While behavioural and chemical programs are in progress, a further complementary approach to the study of any semiochemical system involves an examination of the semiochemical source and of factors which modulate that source s activity in ways which could be semiochemically significant (Adams, 1980). 

In the use of both wind tunnels and olfactometers, a comparative approach is used. In the two-arm olfactometer, for example, the simplest analysis would be to compare the number of times that the arm with the semiochemical is chosen relative to the control arm and test these numbers statistically with a chi-square or G-test (Sokal Rohlf 1995) against the null hypothesis that the two arms will be chosen equally. In wind tunnels, an equally simple analysis would be to test for more or faster movement in the upwind direction when the test chemical is released into the airstream than when it is not. In both cases, however, care must be taken in the design and operation of the apparatus to avoid biases in the data, as follows. 

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