THE TOLL OF INSECT PESTS.

Otago Witness, Issue 4039, 11 August 1931, Page 12

THE TOLL OF INSECT PESTS.

Scarcely any part of a plant is free from insect attack. The turnip fly pounces upon young cruciferous crops directly the young plants appear above ground. Leaves are specially susceptible • —sandfly larvae give leaves a scorched appearance, gall insects promote swelling, and the larvae of moths coil up leaves for their chrysalids, while caterpillars riddle leaves with holes. Blossoms are destroyed by beetles and aphides, while bark beetles and other borers take toll of stems and woody’ trunks. The wireworm is the chief enemy of the roots of crops, but it has many helpers. The loss sustained by’ farmers on account of insect pests must be very large. Accurate iigures upon the subject are, of course, impossible to obtain, but every authority is agreed that insects do take a tremendous toll upon crops of almost every kind, and also that a large amount of the damage caused by these pests is avoidable. With regard to the insects which prey upon our farm crops, we have to remember that modern methods of farming are largely to blame for the damage which they cause. When man turned his attention to agriculture, and began to grow crops close to one another, and to fertilise them, he upset the balance of Nature very considerably. If a cropped area were left to itself for

a number of years it would gradually develop a vegetation different from that which was arbitrarily placed upon it. It is only natural that an insect which feeds upon a particular plant is likely to flourish in and be attracted to a paddock carrying an abundance of its favourite food —such, for instance, as millions of wheat plants or of turnip plants—and be doubly pleased when it finds that the farmer has provided an excellent home for it during the winter in the shape of a hedgerow covered with rank grass and full of nice crevices and clods. When a farmer lays down a paddock to a long period of grass he is doing the best possible thing for the wireworm and leather jacket. The eggs of these pests are laid in rough grass land, and hatch out into grubs or larvae, and at once commence to feed on the grass roots. Their presence is not usually detected whilst the land is. under grass, because grass has such extraordinary powers of recuperation, due largely to its system of fibrous roots. When the land is ploughed and a crop of oats or potatoes is planted, these pests (wireworm and leatherjackets) seem to matrialise from nowhere, and play havoc in the crop in a very short time. Little is heard of the wireworm at present, because farmers are not breaking up grass land very freely, but are putting down arable land to pasture._ Careful management will go far to minimise harmful results. The depredations of the turnip flea beetle or “fly” are well known. This animal passes the winter sheltering in weeds and hedgerows, and begins to multiply in numbers only when a sufficiency of food becomes available—viz., when the turnips are just coming through the ground. The good farmer is likely to get off more lightly than tiie bad farmer. Why ? Because the most vulnerable period in the turnip’s existence is whilst the two seed leaves (smooth leaves) are the only ones showing. If the fly attacks these at all badly the plant succumbs, because it has no reserves to draw upon. When the rough leaves begin to appear the plant has a greater chance of living. The turnip seedling will grow most rapidly if the tilth is fine, and there is a generous fertilisation with a soluble manure, so that a well-prepared seed-bed is really one of the best insurances against fly. Then too, the “ fly ” is very intolerant of dust in any form, and on a dry day. if the surface of the soil be fine, a considerable dust can be created by twiggy branches attached to a cultivator, and this dust, settling on the plants, drives off the insects. This practice is, says a Home exchange, often more beneficial than dragging sacks soaked in paraffin oil over the plants. Be that as it may, good farming is in itself tlie best preventive of insect pests. Unfortunately, the property of a good farmer is always liable to suffer from the attentions of insect pests bred upon his neighbour’s farm.

Fortunately, .Nature is at hand to help the man who cultivates the soil. Some insects should be encouraged. Ladybirds devour all kinds of plant lice (aphides). Many insects lay their eggs in the larvae of Hessian flics and various other pests. Insectivorous birds must be looked upon as the farmer’s chief friends. Starlings and minahs, rooks and magpies destroy a vast number of grubs and other forms of insect life. Some do certainly take toll of fruit and seed, but they do more good than harm. Sparrows do an enormous amount of good even if hard on the farmer’s grain at harvest time. During the rest of the year they are eating waste food or weed seeds, and during the breeding season both parents are busy carrying insects to their voracious nestlings. As Dr Hilgendorf points out in his book on “ Farmers’ Foes in New Zealand,” pests of various sorts have a distinct tendency to be worse in new countries. Man comes and brings with him new plants, which provide new and unaccustomed food to native insects, which thus multiply far beyond their original proportions —for example, the brown beetle. Or, he introduces a new insect, which multiplies freely in the absence of the bird that kept it in check in its home country, or in the absence of its accustomed parasite—for example, the bluegum scale. Or, he introduces a new bird to keep down the insects, and the bird increases disproportionately, because the birds and beasts of prey that live cn it in its home have been left behind—for example, the sparrow, until the owl was introduced, was much commoner here than in England. Now the owl has become a problem. Thus man is con-

tinually upsetting the balance of Nature, and continually having to take steps to restore that balance.