INSECT PESTS

Taranaki Daily News, 23 December 1931, Page 16

INSECT PESTS

GRUBS AND BEETLES SOME SUMMER PLAGUES. HUGE ECONOMIC LOSS. The Dominion, fortunately, has no insect plagues comparable to the plagues of locusts which sweep over some countries, with disastrous results to everything green. But it docs have some rclatively e ’minor insect plagues, which collectively result in great economic loss to the country. One of these figured in the news recently, when a message from Te ' Aroha stated that “although the plague of grass grub beetles is showing signs of abating, the ravages of these pests have extended to practically every farm in the neighbourhood. The presence of such enormous swarms indicates an even greater danger from both the grub and the beetle next year, when the eggs deposited in the soil have hatched. However, one need not go as far afield as Te Aroha to hear about grass grubs; many an owner of a lawn in this district can, and does, speak feelingly on the subject. What are commonly known as grass grubs, larvae which do such immense damage to pastures by eating the roots of the grass, are the forerunners of a beetle belonging to the cockchafer family. The immense insect family boasts of the name of Melolonthina. There are a. thousand species of the family in Australia; New Zealand is more than content with a mere 60 or eo. That the cockchafer is a lainellieorn coleopterous insect interests few besides entomologists, but anyone concerned with pastures is compelled to take an interest in its life history. As a winged insect, the cockchafer’s life is short; but during that brief span, especially when swarming in countless thousands, it can manage to do a, great deal of damage to succulent foliage. DOING HAVOC AMONG THE ROOTS. But it is in the larvae stage that cockchafers do most damage, and this stage in some cases lasts several years. In New Zealand the common grass grubs’ are larvae of the genus known as Odontria, the commonest species being O. zealandica. There is also O. striata, which produces eventually a somewhat larger and darker brown beetle. The larvae live and feed among the roots of the grasses, doing immense havoc. They have no natural enemies apparently, except birds. Starlings are excellent searchers for and finders of grass grubs, and literally go over every inch of the lawn in their °search for them. “The plague of beetles” referred to above is the result of the metamorphosis of the grass grub larvae. In due course of time, the beetle, having eaten its fill of dainty green will deposit its eggs in the ground and the cycle and the trouble starts all over again. 1 . A . But there is an even worse pest than the grass grub and its subsequent cockchafer, and that is the bronze beetle, an insignificant little chap (about the size of this letter O) considering the damage that it can do. Although its larvae live on grass roots, like those of the cockchafer, they do not appear to do any appreciable damage. In this case it is the adult insects which cause the havoc. When, in 1769, Captain Cook visited these shores, he had with him Sir Joseph Banks, the famous naturalist. Banks was much more interested in plants than in beetles, but during his six months’ sojourn here the bronze beetles, by sheer force of numbers, thrust themselves upon his notice, and he felt constrained to record their presence. At that time the bronze beetles chewed the leaves of native shrubs and trees, for the simple reason that it was a choice between them and starvation. INSECT CHANGES ITS DIET. But with the advent of the white man and his imported plants, th® bronze beetle changed its diet, and now, whenever and wherever he gets the chance, it does incalculable damage to apple and pear crops and to small fruits. Other trees, too, it will strip bare of foliage, with the result that it is one minion. It has been estimated that a of the major insect pests of the Doserious infestation of an orchard may result in the destruction of 40 per cent, of the annual crop. The worst damage that the bronze beetle does is to the fruit of apples. These are attacked at a very early stage; the beetles nibble them, and large scabs form. This causes abnormal growth in the fruit, which is rendered unfit for export. Short-stemmed varieties of apples, which provide shelter for the beetle, are most readily attacked. Thus Cox’s are an especial favourite, while the long-stemmed Delicious apples are scarcely damaged. Small fruits are damaged in various ways; the stems of the clusters of currants are so much eaten that the half-ripe fruit withers and falls; o-ooseberries are eaten through to the pulp; the leaves and fruit of cherries are attacked; with raspberries the half-formed fruit is eaten, but the most serious damage is that of defoliation, which may completely ruin the late crops. When it turns its unwelcome attentions to foliage, the bronze beetle first attacks the under surface, gradually eating through to the upper side and riddling the leaf with small holes. Plum trees and other trees are sometimes completely defoliated. 1 QUESTION OF CONTROL. After a short life and a gay one, having done damage out of all proportion to its size, the lady bronze beetle deposits her eggs in little earthen capsules in the ground. Uncultivated soil is much preferred as an incubator and nursery, hence one of the most important factors in control is the cultivation of the soil. In fact, this at present seems about the only method of control. The adult insects are on the wing from November to January, and have a wide distribution over the Dominion. They are more abundant in some localities than others, and are to be found, from sea-level up to an altitude of 2000 to 3000 feet. How far they fly is not known, but probably the prevailing westerly winds are a factor in their establishment in the important orchard areas on the East Coast. They certainly appear to migrate down the prevailing wind from an infected and carelessly kept orchard to clean areas. The bronze beetle (Eucolaspis Brunnea) is also known as the “flea-beetle,” its enlarged hind legs enabling it to jump. It is of a shiny brown colour, and is unfortunately far too well known to the orchardist. The layman, however, sometimes confuses it with other and larger destructive beetles, such as those emanating from the grass grub as mentioned at the beginning of this article.