Biological management methods reduce insect pest abundance and damage by use of natural enemies. Natural enemies include predators, parasites, and pathogens that kill insect pests. Natural enemies can be used in three ways: classical or importation is control of insect pests using introduced natural enemies, augmentation is mass culturing and periodic release of a natural enemy, and conservation or preservation is enhancement of numbers of already existing natural enemies. Conservation currently is the most applicable biological management method to suppress abundance of sorghum insect pests.
Conservation of natural enemies
Conservation of natural enemies involves protecting existing natural enemies so they are abundant enough to suppress the insect pests they attack. Sorghum hosts an abundance of natural enemies, primarily because of aphids that infest the crop. The corn leaf aphid, usually noninjurious to sorghum, often becomes very abundant. Corn leaf aphids attract many natural enemies that attack and reduce the abundance of aphid and caterpillar pests. However, most insecticides used in sorghum are broad spectrum and kill natural enemies as well as pest insects. The negative effect of insecticides on natural enemies is a primary reason for making certain insecticides are needed before they are applied. When natural enemies are destroyed, there is no natural protection against insect pests. This results in resurgence of the treated pest or allows a secondary pest such as corn earworm or Banks grass mite to increase in abundance.
Sorghum insect pests most affected by natural enemies are greenbug, yellow sugarcane aphid, corn earworm, fall armyworm, sorghum webworm, and Banks grass mite. Predators affect the abundance and rate of increase of greenbug, especially during early season, and often prevent economic damage. This is true particularly when greenbug-resistant hybrids are used. Parasites often terminate greenbug infestations late in the season. Predators suppress the abundance of corn earworm and fall armyworm that infest sorghum panicles. The sorghum midge is attacked by several parasites, but their effect is minimal. Several pathogens, mostly fungi, infect insect pests. Chinch bug, corn earworm, and fall armyworm are insect pests most affected by naturally occurring pathogens.