Approaches and Objectives

Many of the problems involved in understanding the underlying processes and mechanisms of cultural control are fundamental to the ecology of insect/host interactions and thus are of immense interest to some ecologists: for instance, the role of insect dispersal in the colonization and exploitation of crop plants. It is this interest in ecological principles that has pro duced some of the more illuminating work on the processes involved in cultural control. Knowledge and understanding of these processes will enable entomologists to predict more accurately the potential value of similar control techniques in other unstudied systems. For the large part, however, research into cultural control revolves around the evaluation of various combinations of practices and techniques for specific crop systems. These studies make little or no attempt to identify the processes that account for the differences between treatments. While there is a need for both approaches, it would be difficult, and often impossible, to predict the wider value of new techniques and practices using the latter approach. There has been a tendency for a greater emphasis to be placed on limited evaluations of treatments rather than on experiments to evaluate processes and as a result, cultural control is often considered to include a mismatch of techniques that can have no cohesive relations. However, over recent years more has been done to develop an integrated philosophy based on a greater knowledge of the host, crop/pest biology and their underlying ecological principles, providing a framework for a more integrated approach in the future.

The approaches that are currently influencing the development of semiochemical use are referred to as 'push-pull' or 'stimulo-deterrent diversionary' strategies (SDDS) (Smart et al., 1997; Miller and Cowles, 1990). These are perhaps best explained through example. Semiochemicals can be used in a variety of different ways to control pests: the harvestable crop can be protected by means of repellents, antifeedants or egg-laying deterrents ('push'), and parasitoids and predators are attracted in to mop up pests undeterred by the protectants ('pull'). At the same time, aggregative semiochemi-cals, including host plant attractants and pheromones, stimulate pests to enter traps or to colonize a trap crop ('pull') where selective chemicals or biopesticides are applied (Smart et al., 1997). Such strategies provide a framework for a systems approach to semiochemical R&D that promises much more than that based on an isolated independent development of semi-ochemical products. The opposite is almost true for the sterile insect technique SIT, however, where having identified an approach (chemo-autosterilization) that has general applicability, target/sterilization systems need to be developed on a case by case basis.

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