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Since the 1950s, growing cotton in Israel, has been associated with many pesticide applications, mainly against the whitefly, Bemisia tabaci (Gennadius), the Egyptian cotton leafworm, Spodoptera littoralis (Boisduval), the pink bollworm, Pectinophora gossypiella (Saunders) and the spiny bollworm, Earias insulana Boisduval. In the mid-1980s, the efficacy of insecticides for controlling B. tabaci and S. littoralis declined gradually, resulting in increasing numbers of applications and a risk to the economic viability of the crop. As a consequence, in 1987, an insecticide resistance management (IRM) strategy was established in cotton. The main purpose of the strategy has been to combat resistance to currently available and efficient insecticides (e.g. endosulfan and pyrethroids), to prolong the life span of new insecticides by optimizing their use and to preserve natural enemies during the peak of their activity. Based on the Australian experience, the growing season was divided into four periods with each of the available insecticide groups allocated to them. An alternation programme was applied with insecticides of different modes of action, rotated on a per generation basis (approximately one month) of the relevant pests. Insecticides with novel modes of action such as buprofezin, pyriproxyfen and diafenthiuron for controlling the whitefly B. tabaci, and benzoylphenyl ureas against lepidopteran pests, were introduced into Israeli cotton in the 1990s. The introduction of these insecticides was accompanied by an extensive resistance monitoring programme for major cotton pests conducted during the summer. The rational use of insecticides since the introduction of the strategy has resulted in maintaining the susceptibility of the cotton pests to the various groups of insecticides along with a substantial reduction of insecticide applications in the cotton fields.
The Israeli IRM strategy incorporates the following objectives: (1) rational use of the existing insecticides; (2) development and optimal use of new products; and (3) reducing reliance on pesticides through alternative control means such as biological and cultural methods (Denholm and Rowland, 1992). This strategy aims to cope with resistance problems in a pest complex, since each chemical application can affect outbreaks of secondary pests and potentially harm beneficials. One of the achievements of this strategy is the reduction in control expenses and in insecticide use (from an average of 16 to 5 applications) against the entire range of cotton pests (Fig. 4) (Forer, 1990; Horowitz et al., 1994). Reduction in chemical treatments will inevitably reduce the risk of resistance development. Acceptance of a rational pest-control management programme by the cotton growers, improvements in scouting for pests and the increasing knowledge about natural enemies are important factors for a successful IPM-IRM strategy. In addition, the introduction of novel efficient and selective insecticides, which do not harm parasitoids and predators, was essential in achieving the reduction in the number of treatments.
One of the handicaps faced by the Israeli cotton strategy is that growers of other field crops have not yet adopted a similar strategy. Hence, insecticide applications to other crops may affect the entire resistance level and impair the sincere efforts of cotton growers in implementing the strategy. However, cotton is one of the major crops in Israel and has its own impact. We have begun implementing similar strategies for other field crops.
Another problem of this strategy arises from the obligatory use of non-selective insecticides for controlling the PBW and spiny bollworm in midsummer. These insecticides interfere with the ecological balance, they are harmful to beneficials and they may cause a build up of earlier attacks by other pests (such as B. tabaci). The attempt to control bollworms with IGRs had only moderate success under field conditions (Horowitz et al., 1992b; A.R.H., unpublished data).
Transgenic cotton plants which express the toxin of Bacillus thuringiensis may successfully affect bollworms such as PBW and E. insulana (R.T. Roush, pers. comm.) without harming natural enemies. Hence, such a technology could be beneficial to the Israeli IPM-IRM strategy.
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