The pest management should be done at

Answer: Option B

Pest management should be done at the Economic threshold level.
An economic threshold is the insect's population level or extent of crop damage at which the value of the crop destroyed exceeds the cost of controlling the pest.
The pest density at which management action should be taken to prevent an increasing pest population from reaching the economic injury level. EILs are usually expressed as a pest density and are developed from yield-loss relationships.