In India, the spread of Opuntia was controlled by

Options

(a) introducing insects
(b) spraying D.D.T.
(c) letting loose cattles
(d) growing trees

Correct Answer:

introducing insects

Explanation:

The control of pests by biological (rather than chemical) means is achieved by breeding disease-resistant crops or by introducing a natural enemy of the pest, such as a parasite or predator, e.g. control of the prickly pear cactus (Opuntia) was done by introducing the cactus moth (Cactoblastis, Cactorum) whose caterpillars feed on the growing shoots of the plants.