There are three primary methods of using biological control in the field: 1) conservation of existing natural enemies, 2) introducing new natural enemies and establishing a permanent population (called "classical biological control"), and 3) mass rearing and periodic release, either on a seasonal basis or inundatively. So, microbial agents are highly specific against target pests so they facilitate the survival of beneficial insects in treated crops. This may be the main reason that microbial insecticides are being developed as biological control agents during the last three decades.

Microorganism as bacterium, fungus, virus or protozoan as the active ingredient can control many different kinds of pests, although each separate active ingredient is relatively specific for its target pest and there are fungi that control certain weeds, and other fungi that kill specific insects. Some microorganisms contribute to insect nutrition, by providing nutrients or degrading plant material intractable to insect digestion. Resident microorganisms protect their insect hosts against natural enemies, including viruses, bacteria, and parasitoids, by synthesizing toxins or modulating the insect immune system. The bio-agents such as Bacteria- (Bacillus thuringiensis), Fungi (Beauveria, Metarhizium, Verticillium, Nevorium), Virus (NPV), etc are widely used for control of various pests in agriculture. These bioagents will produce non-toxic biological material (protein) which is harmful to pests. There are three primary methods of using biological control in the field: 1) conservation of existing natural enemies, 2) introducing new natural enemies and establishing a permanent population, and 3) mass rearing and periodic release, either on a seasonal basis or inundatively. Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also involves an active human management role. Biological control is a method of plant disease management by inhibiting plant pathogens, improving plant immunity, and/or modifying the environment through the effects of beneficial microorganisms, compounds, or healthy cropping systems. Biological control, the use of living organisms to control pests. A natural enemy such as a parasite, predator, or disease organism is introduced into the environment of a pest or, if already present, is encouraged to multiply and become more effective in reducing the number of pest organisms.