Book excerpt: Of the nearly one million known species of insects, about 15,000 species are considered pests and about 300 require some form of control. Fortunately, most insect pests have pathogenic microorganisms associated with them. There are two aspects of economic problems caused by insects.One concerns the loss of production that results from damage to crops and to the health of human and domestic animals, the other concerns the cost of attempt to prevent or control such production loses. At the same time with increasing agriculture, insects become more and more important competitors of human food damaging or even destroyingthe crops. Mosquitoes and black flies are a constant threat to health and comfort, yet the chemical pesticides used to control them have created serious ecological problems. Environmental and health concerns about the application of chemical insecticides to reduce large-scale insect pest infestations have led to renewed interest in the development of microbial agents for incorporation into integrated pest management strategies for the control of acridids.