**2.2 Types of insect resistance**

Insect resistance on the other hand is typically governed by three main mechanisms.

#### *2.2.1 Single or oligogenic resistance*

Single or oligogenic resistance has been observed against some insects such as Hessian fly in wheat. Such resistance is governed by a single or few major genes. This type of resistance has also been reported against Russian wheat aphid and green bug.

#### *2.2.2 Polygenic resistance*

Several genes with small additive effects govern the resistant response against some insects. The resistance observed against cereal leaf beetle in wheat is of this type.

#### *2.2.3 Cytoplasmic resistance*

Cytoplasmic resistance against insects has not been reported in case of wheat. However, in maize resistance against European corn borer is governed by cytoplasmic genes. Another case of cytoplasmic resistance is observed in lettuce against root aphid.
