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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.
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