**2. History of resistance to insecticides**

Resistance to insecticides by insect pests has been documented for over 75 years, but its greatest impact has occurred during the last 30 years following the discovery and extensive use of synthetic organic insecticides [7]. Insect resistance was first observed in 1908, reported by Melander [8] in the San Jose scale insects *Aspidiotus perniciosus*, found to have become insen‐ sitive to lime-sulphur. Thirty years later, there were further reports of insect resistance towards numerous other pesticides.

When dichlorodiphenyl-trichloro-ethane (DDT) was introduced in 1946, insect resistance to the compound appeared quickly and worldwide. The first sign of resistance towards DDT was shown in the housefly *Musca domestica* [9]. Thereafter, cases from different locations were reported: *Aedes sollicitans* in Florida, *Culex pipiens* in Italy, and *Cimex lectularius* in Hawaii [1]. New insecticides that were later introduced did not last long with regard to their usage as the number of species showing resistance to one or more toxicants doubled every six years between 1948 and 1983 [10].

A number of resistant species are also reported in other agriculturally important orders such as Lepidoptera (67 species, representing 15%), Coleoptera (66 species, representing 15%), Acarina (58 species representing 13%), Homoptera (46 species, representing 4%), and Heter‐ optera (20 species, representing 4%) [11]. However, studies have shown that resistance develops faster in insects with many generations per year rather than only one, at higher selection pressures than at lower ones. Sawicki [12] noted that resistance is regarded as a problem only when the cost of control becomes unjustified or when excessive use of the control agent presents health and environmental hazards.
