The resistance problem is the greatest single challenge facing applied entomologists today, because of the widening circle of cross and multiple resistance among insect pests, the diminishing number of effective commercial insecticides and the exponentially – increasing costs of development of new insecticides. In 1938, there were already 7 species that were resistance to insecticides. In 1988 there were closed to 500 resistant species. More significantly, insects with multiple resistance are becoming increasingly common. This often occurs when different groups of insecticides interfere with a common target that has changed.