Another major cause for large scale destruction of crop plant and crop produce is insect and pest infestation. Insect resistance in host crop plants may be due to morphological, biochemical or physiological characteristics.
Hairy leaves in several plants are associated with resistance to insect pests, e.g, resistance to jassids in cotton and cereal leaf beetle in wheat. In wheat, solid stems lead to non-preference by the stem sawfly and smooth leaved and nectar-less cotton varieties do not attract bollworms.
High aspartic acid, low nitrogen and sugar content in maize leads to resistance to maize stem borers. Breeding methods for insect pest resistance involve the same steps as those for any other agronomic trait such as yield or quality and are as discussed above.
Sources of resistance genes may be cultivated varieties, germplasm collections of the crop or wild relatives. Some released crop varieties bred by hybridisation and selection.