Degree of resistance

• Resistance can be measured in terms of plant infestation level, damage inflicted, and crop loss. Painter (1951) classified the degree of resistance and degree of damage in the following manner.

i. Immunity: A variety that cannot be infested or injured at all by a specific insect species under any unknown condition. Such a type of host behaves like a non-host in which insect pests do not show up at all. The losses are about zero.

ii. Highly resistant: Varieties that suffer little damage by a specific insect species under a given set of conditions Usually, wild plant genotypes possess a high level of resistance to insect pests. The losses are about 10-20%.

iii. Low level of resistance: Some cultivars of some species are damaged less by a pest than the average (cultivated varieties) damage for the crops. Usually, many of the landraces have some level of insect resistance. The losses are about 20-40%.

iv. Susceptible: Varieties that show average or more than average damage by an insect e.g. Reverse of resistance the cross-breed or hybrid crop cultivars are generally susceptible to insect pests. The losses are about 40-60%.

v. Highly susceptible: Varieties that are readily infested with insect pests and suffer considerably more damage than average. Come crop varieties suffer heavily from pest attacks. Such varieties are used as susceptible checks. The losses are more than 60%.