Pesticide applications have also created new pests. Many insects that have been naturally controlled by predators have been released from control when the predators are destroyed by pesticides. The immediate result is that further pesticide application becomes necessary. Repeated applications of pesticides cause evolution of insect resistance to the pesticide. In nature, the pressures of natural selection create a diverse array of species with abilities to cope with a variety of problems.
Pesticide application is another type of selective pressure.
New pesticides have to be created to circumvent the resistance evolved by pests. Since the novel detoxification pathways often have general effectiveness against a class of chemicals, new classes of pesticide may be needed. Over the past century, there has been a rapidly escalating arms race and an ever more dangerous war against crop-devouring pests. Ironically, it is the pests who are winning. Farmers are running faster than ever, but have lost ground.