This is an even greater cause for alarm, however, since resistance to more than one compound usually means that the pest is harder to control. Resistance is probably the major contemporary problem in control of vectorborne diseases, particularly malaria, in most countries. When pest organisms are resistant to one class of pesticide compounds, they may evolve resistance more rapidly to new groups of chemicals having either similar modes of action or similar metabolic pathways for detoxication. There is particular concern that the pyrethroids may have a short useful life against many pest species because of a gene identified as kdr. This gene played a key role in the genetic evolution of DDT resistance and appears to provide certain insects with protection against pyrethroids.
Pesticides remain effective in many areas where selection has been less severe.
On the Atlantic coast of Central America, Anopheles albimanus can still be effectively controlled by organophosphates and carbamates. In the Midwest these compounds also control the Colorado potato beetle, which is resistant to every insecticide applied to control it on Long Island. Resistance to insecticides has not yet been detected in the European corn borer, but this is an exceptional case. Nevertheless, agricultural production and public health programs can no longer rely on a steady stream of new chemicals to control resistant pest species. New compounds that are superior or have different modes of action are difficult to discover and are increasingly expensive to develop.