Degree of resistance

• Resistance can be measured in terms of plant infestation level, damage inflicted, 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 type of host behaves like non-host in which insect pest do not show up at all. The losses are about zero.

ii. Highly resistant: Varieties which suffer little damage by a specific insect species under a given set of condition. Usually, wild plant genotypes possess 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 land races have some level of resistance to insect. The losses are about 20-40%.

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

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