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Plutela Cruciferarum

A small moth, known also as the Diamond-back or Turnip-moth, belonging to the group of Tineina. It is excessively common throughout Great Britain; and, despite its small size, the ravages committed by the larvae in some years are sufficient to force it on the notice of every observant farmer and gardener. The wings are about 5/8in. across. They are narrow, with long fringes, and are of a greyish-brown colour, with darker spots, the inner margin bearing a long, pale ochreous streak, with three prolongations into the dark part. While at rest, the moths sit in a very characteristic attitude, with the antennae held straight forward, and nearly touching their support, and the wings folded over the body, like the sloping sides of a roof. The pale edges are thus in contact, and resemble a row of three diamond-shaped spots. The legs are nearly hidden by the wings in the sitting insect. The larvae are pale green in colour, with a darker head, several black dots on the next segment, and two yellowish spots on each of the next two segments. They have a few bristly hairs on the body, which tapers a little towards each end. They feed on the lower surface of the leaves of Turnip, Cabbage, and other Cruciferae, eating away the substance of the leaf between the veins. Frequently, a dozen or more may be found on a leaf, and, when very numerous, or while the plants are small, the crop is apt to suffer severely. When full-fed, the larvae spin slight cocoons in the hollows between the leaf-veins on the lower surface, or on the soil, among rubbish, and change into pale brown pupae, marked with black lines on the back and wing-cases. The moths emerge in from two to three weeks. There are two chief broods in the year, the moths appearing in May and August, and the larvae about a month or six weeks later.

Remedies. These are very difficult of application, since the larvae live protected by the leaves from the direct application of insecticides, while their numbers and small size render hand-picking slow, and unlikely to be successful, except on a small scale. The removal and destruction of leaves, with numerous larvae and pupae on them, and also of surface rubbish in autumn, lessens the risk to future crops. Brushing below the plants with branches of Firs, or of other twiggy shrubs or trees, has been recommended as likely to remove a number of the larvae. Whatever favours rapid growth in the plants, e.g., manures and watering the plants in dry weather, will be of service; and gas lime and soot, thrown below the plants, might assist in keeping away the moths during the time of egg-laying, and in reducing the injury to the leaves.