WAYS OF THE WILD.

Auckland Star, Volume LXIV, Issue 88, 15 April 1933, Page 1 (Supplement)

WAYS OF THE WILD.

JHE WHITE BUTTERFLY.

A SERIOUS PEST.

(By A. T. PYCROFT.)

Miss M. Constance McGregor las sent me a specimen of the white butter, fly, -which was caught by her father at Gisborne. Miss McGregor states that this butterfly has become a serious pest all over the Gisborne district, and on the day the specimen sent to me was captured they were so numerous as to resemble a snowstorm, and that it is now quite hopeless trying to grow cabbages there. The butterflies are seen hovering over the flower beds. Miss McGregor thinks that our mild climate may prove a suitable home for this pest. The cabbage butterfly, Pierisrapae, of Europe, and now of America, where it was first seen at Quebec in is in its larval or caterpillar stage the most destructive among the many insect and other enemies of cabbage and related crops. There is also a native American species, Pieris. oleracea, which is also injurious to members of the Brassica or cabbage family, from which the various species of cabbage, cauliflower, broccoli, etc., have been derived. In America the cabbage butterfly appears to favour no part of the country more than another, being as plentiful _ in Canada and New England as it is in the Gulf region. Description of Butterfly. The butterfly has a wing expanse of nearly two inches. It is white, marked with black near the tops of the_ forewings. The female has two conspicuous black spots on each fore-wing, whereas the male has only one. The under-side of the hind-wing is of a uniform strawyellow colour, of satiny appearance, and in both sexes there is usually an indistinct black spot near its top. The body of the female is whitish, that of the male is usually darker on the back. The male is usually smaller than the female. The eggs are spindle-shaped, of a pale yellowish colour, strongly ribbed and large enough to be seen Teadily with the unaided eye. They are laid, by the butterfly singly, on end, and usually on the under side of the outer leaves of cabbage and other food plants. The caterpillar is velvety green, or of about the same colour as the cabbage on which it feeds. There is a faint yellow stripe down the middle of the back, and a row of yellow spots along each side in line with the breathing pores. The surface of the viewed through a hand lens, is seen to be somewhat rough and finely dotted with small black spots. It measures, when full grown, about an inch and a quarter in length. When the caterpillar, or worm, becomes fully grown it attaches itself to a cabbage leaf or other nearby object by means of a thread-like girdle of silk, and is soon changed to a chrysalis—an inactive stage. The Chrysalis, The chrysalis is a little less than three-fourths of an inch long, varying in colour, through dirty grey to yellow, green and dark grey. The caterpillar, which hatches from the egg, eats greedily and grows rapidly, reaching maturity in from ten to fourteen days after hatching. It moults four times. Thereare, therefore, five distinct stages of growth, the first moult taking place in the warmest weather, in about two days froin the time of hatching; the second stage lasting from two to three days, the third and fourth from one to two days each, and the.fifth from four to five days. In the summer time the chrysalis period iasts from seven to twelve days. In the colder climates the insect passes the winter as a chrysalis, and the butterflies appear the following spring. I have no knowledge that this butterfly has spread to the South Island. It was first recorded at Napier quite recently. When it reaches the colder parts of New Zealand its chrysalis will no doubt remain dormant throughout the winter. The period of development, egg to butterfly, covers between 22 and 44 days. In cold climates this species is credited with producing three generations in a season, and five or six are reported in a sub-tropical climate. ' Food Habits and Nature of Injury. The caterpillar feeds on all forms of cruciferous plants, being particularly fond of cabbage and cauliflower, and less destructive to turnips, kale, collards, radish, mustard and horse radish. The butterflies sip the nectar of flowers of various kinds, and are commonly seen hovering over them. They are especially fond of the white blossoms of crucifers, and of white asters, lavender, heliotrope and thistle. Like other butterflies, this species is active by day, being on the wing from early morning until near dusk. It is a comparatively slow, but tireless, flyer, capable of journeying long distances. The caterpillar has been rightly termed the bane of the cabbage grower and the dread of the housewife. It begins work early in the season, damaging young plants. After riddling the outer leaves it attacks the tender inner leaves as they form, frequently feeding within the immature heads, and rendering the cabbage unfit for food because of the abundant dark green excrement which it deposits. Before cooking it is frequently necessary to tear the head apart to insure that no disgusting caterpillars are concealed within. In cool •weather the caterpillar often feeds fully exposed on the surface of the leaves in the sunshine. It frequently works into the centre of the cabbage, or other similar plant, attacking the undevelopedheart and rendering it worthless for market. Natural Enemies. Were it not for certain natural enemies, this insect would be a still greater pest in Europe and America. The * most important of its insect enemies are small wasplike parasites, or four-winged flies, the immature forms of which feed within the body of the caterpillar. One of the most efficient of these, the cabbage caterpillar ichneumon fly, was imported into America as long ago as 1883 from England, as a means of controlling the caterpillar. It has more than justified introduction. The cabbage caterpillar, chalcis fly, is also beneficial in controlling the pest. The eggs of this fly are deposited in the caterpillar, hatch into the larvae, and live within it. The adult parasites which develop from them come out from the chrysalis stage of Hie caterpillar. Numerous other insect enemies attack the caterpillar, and it is sometimes subject to a contagious bacterial disease. Birds which arc known to feed on the caterpillars and keep the pest under control arc thrushes, blackbirds and sparrows. It is certain, however, that other birds eat them. Spraying •with arsenical sprays is effective, and it is not difficult to control the pest if these remedies are promptly used.