ABSTRACT
Predatory insects are responsible for severe losses in agricultural production of crop plants destined for consumption by both humans and animals, whether they attack the plants themselves or their harvested products, e.g. seeds. For many years, the indiscriminate use of chemical pesticides on cultivated lands was the only way to reduce the destruction caused by these insects. As a result, many insect species have developed resistance to various pesticides and, because these chemicals are also harmful for humans, their extensive use is now considered a serious health hazard. In addition, the protective effect of pesticides on some plants cultivated on large-scale (e.g. rice) has now become questionable (Hadfield, 1993). More recently, as an alternative to the chemical control of insects, the attention has turned to the exploration of the use of more consumer-and environmentally friendly biological methods for plant protection. Thus, the introduction and subsequent expression of genes in sensitive plants, coding for molecules that are toxic for insects, is now considered to be one of the best methods to protect cultivated plants against these predators. There are several reasons for this: the introduction of a single foreign gene in a transgenic plant may not require considerable genetic changes in comparison with other genetic manipulations such as crossbreeding; the introduced gene can provide continuous protection for the plants; and this protection is independent of the weather; plants which would be difficult to spray with insecticides can be readily protected by this method. Conversely, the protective molecule must fulfil certain conditions, first of all that it must be totally innocuous for higher animals and man. Moreover, the protective molecule must be active at a concentration far below that tolerated by the transgenic plant, in order to be expressed without any deleterious effect on the host plant.
