(1) Cricket. (2) Grasshopper. (3) Caterpillar. (4) Diamond-backed Moth—a, adult moth; b, egg; c, larva; d, pupa. (5) Cut-worm lying by damaged plant. (6) Tomato-worm Caterpillar—a, adult; b, larva. (7) Cabbage White Butterfly—a, adult; b, egg; c, larva; d, pupa. (8) Larva case of Bag-moth.
Though cut-worms are active throughout the growing period of plants, most damage is done to young and tender plants at the time of establishment, and this is particularly noticeable in the spring. When plants are grown isolated in rows, and the area is not too large, complete protection from cut-worms can be secured by enclosing each plant in a tin collar pushed into the ground and projecting a few inches from the surface; these collars are removed when the plant is well established. In localities where cut-worms are very troublesome it is advisable to reduce their numbers by means of a poison bait made as follows:—50lb. of bran and 1lb. of Paris green are thoroughly mixed in a dry state; when this is done, and just before being used, the bran is moistened with water, sweetened with molasses, until the bait reaches a crumbly, but not saturated, condition. This bait may be broadcast over the infected area or laid around each plant as a barrier. This bait must be applied every few days until the plants have reached a stage when they are able to withstand cut-worm attack.
A great deal can be done to check cut-worms by removing dense growths of weeds and rough herbage growing in unused parts of the garden; in such places the insects breed, and are a source of infestation. Another point to consider is that thorough cultivation will destroy many pupæ that are lying underground, and which would otherwise give rise to another generation of moths.
“Army-worms.”—These caterpillars are similar in their appearance and general habits to the cut-worms, but differ in their method of attack. When present in numbers, they move through a crop—especially cereals—eating as they go, and leaving nothing but devastation in their wake, much as does an invading army on the march. They are not of so much interest to the horticulturist as to the farmer.
Tomato-worm (Heliothis armigera).—This caterpillar ([Fig. 10], 6) is one of the most conspicuous caterpillars met with in the garden. Its habit of boring into and eating the contents of tomatoes gives it the name of “tomato-worm.” It is a cosmopolitan insect, and is especially destructive to flower buds and fruit, a wide range of plants being attacked. The caterpillars vary in colour, some being greenish and others brownish, with reddish, yellowish or white markings. The moth, which belongs to the noctuid group, is on the wing both day and night, mostly during the earlier part of the year; it is a stoutly-built insect, measuring somewhat over half-an-inch long; its colour is a brownish-orange, with oblique darker bands on the wings. As the insect passes the winter and spring as a pupa in the ground, thorough cultivation will help to destroy a considerable number. The use of arsenate of lead sprays, however, is the most effective control for the caterpillars.
Hawk or Sphinx Moth (Sphinx convolvuli).—This conspicuous insect and its caterpillars are most abundant in the Auckland province, though found as far south as Christchurch. The caterpillars feed on convolvulus, but do considerable damage to the foliage of the kumara and sometimes tobacco. The caterpillar is the largest met with in the garden; it is stout in form, and measures up to 3 ½ inches when fully grown. It is to be recognised at once on account of the dark red, horn-like process arising from the end of the body. The caterpillar may be of two colours—the one green, with diagonal yellow bars on the sides; the other, brownish-yellow, with dark lines on the back and sides. From about February to November the insect lies in the ground as a pupa. The latter can be recognised by a curved process arising from the head and lying along the body. The moth flies rapidly during the last and earlier months of the year; it is a large, conspicuous insect, about 1 ½ inches long, with greyish-brown mottled wings, while the abdomen is conspicuously barred with white, red and brown. Arsenate of lead against the young caterpillars during November to February would act as an efficient control.
Cabbage White Butterfly (Pieris rapæ).—This butterfly ([Fig. 10], 7) is a recent importation, having been first noted at Napier in 1930. Since then it has spread with marvellous rapidity throughout the North Island, and has appeared in the South Island, in the vicinity of Timaru.
The caterpillars of this insect are particularly severe in their attacks upon the foliage of cabbages and cauliflowers, though they also feed upon many other related plants, such as lettuce and radish, besides cruciferous weeds. The caterpillars of the white butterfly are not to be confused with those of the diamond-backed moth, already described. The full-grown white butterfly caterpillar is a conspicuous insect, and measures up to an inch and a-quarter in length; it is easily distinguished by its leaf-green colour and velvet-like appearance, while down the centre of the back is a narrow orange stripe, and on each side a brownish line formed of little spots. The chrysalis measures about three-quarters of an inch long, having a pointed process from the head, and a keel-like ridge on its back, while the colour varies according to the surroundings with which the chrysalis blends; it is not protected by a cocoon of silk, and may be found upon the food plant or any other support near by.
The butterfly itself is a very conspicuous insect, measuring about two inches across the expanded wings. The female is of a yellowish-white colour, with darker to blackish markings at the fore-angles of the front wings, while there are two similar spots on the surface of the same wings, and one on the hind pair. The male is whitish, with a dull greyish-green or bluish hue, marked much as the female, except that there is only a single spot on the surface of each wing.