Pest population level at which management action should be taken -

Correct option is B

· Correct answer: (b) ETL
· ETL (Economic Threshold Level) is the pest population level at which management action should be taken to avoid economic loss.
Other options:
· (a) Insect equivalent: Not the correct term for the threshold in pest management.
· (c) EIL: EIL (Economic Injury Level) refers to the level at which damage becomes significant, but ETL is used for management action.
· (d) Gain threshold: Not used in pest management context.