On rape they may also feed on the flowers and stems, and strip the outer layers from mature seed pods , resulting in poor seed development. The small, slender, gray-brown moth can be recognized by a pattern of cream colored, diamond shaped markings on its back when the wings are folded, and by the upward and outward flare of the wings at the tip. The hind wings have a fringe of long hairs. The diamondback moth does not overwinter in Canada, but is carried northward each year from the United States by southerly winds, usually in May and June. The eggs are laid singly or in small groups, generally on the upper leaf surfaces of host plants.
Older larvae feed mainly from the undersurfaces.
Their characteristic habit of actively wriggling backward and of dropping from the leaf on a silken thread when disturbed, distinguishes them from the larvae of other cabbage-infesting species. After feeding for about 2 weeks, the larvae spin delicate open lacework cocoons , which are attached to the leaves and stems of the food plant. The larvae and pupae are subject to attack by many parasites and predators, including other insects, mites, spiders, and birds, These and weather conditions regulate diamondback moth populations. If chemical control becomes necessary, this should be done in accordance with the recommendations of the provincial Department of Agriculture.