(Pieris rapae).

This conspicuous and easily recognised butterfly was accidently introduced into New Zealand in 1930. It first established itself in Hawke's Bay. Within six years it had spread over New Zealand and was soon regarded as the major insect pest of brassica crops. Since its entry into this country the butterfly has been the object of much research. Successful control measures have been developed using chemical insecticides and many investigations have been made into the possibility of controlling the butterfly by means of parasites, predators, and diseases. Introductions of parasites from overseas have been made into New Zealand and today biological control of the white butterfly is so efficient that no insecticide or other control measure is required in agricultural brassica crops. Biological control is being obtained by a small wasp which parasitises the caterpillar, by another small wasp which attacks the pupa, and by a naturally occurring virus disease which attacks the caterpillar.

by Roy Alexander Harrison, D.SC., Senior Lecturer in Agricultural Zoology, Lincoln Agricultural College.