CONTROL OF PESTS

New Zealand Herald, Volume LXXI, Issue 21845, 6 July 1934, Page 3

CONTROL OF PESTS

DAMAGE BY MEALY-BUGS SAP-SUCKING INSECTS LIFE-HISTORY OUTLINED No. I. The life-history and control of mealybugs are discussed by Mr. David Miller, assistant director and chief entomologist, in the latest bulletin from the Cawthron Institute. Native species of mealy-bugs, he says, aro of little economic importance, the introduced types being responsible for most of the serious infestations. Mealy-bugs belong to that vast assemblage of insects (including scale insects and plant lice or aphides) which have the mouth parts modified as delicate piercing stylets, by means of which plant tissues are punctured and the nutrient sap sucked up, Mr. Miller points out. Not only do mealy-bugs and their relatives weaken the infested plants by draining the sap, but they also cause destruction of chlorophyll, interfere with tho normal functioning of the stomata, and have a toxic influence upon the tissues; further, many serious plant diseases are carried and spread by these insects, while the feeding punctures may give access to the spores of disease. Indication of Presence The presence of sap-sucking insects is very often to be detected by tho stickiness and blackened appearance of the infested plants; this is due to the insects excreting a sweet, sticky substance known as "honey-dew," which collects on the foliage and branches, while upon it grows a black sooty mould. Mealy-bugs may bo readily recognised by the characteristic white mealy substance of a waxy nature that covers and protects the body, continues tho bulletin. Further, this powdery covering is developed as a fringe of leg-like processes at the sides, while those at the posterior end of the body may be prolonged as tail-like appendages of varying length in some species, or they may be no longer than tho marginal fringe in others. Mealy-bugs tend to congregate in colonies and are commonly found attacking apple, pear, citrus, grape and passion vines, as well as a number of ornamental trees and shrubs. Apart from weakening plants during severe infestations, the presence of even a few mealy-bugs on apples or pears, upon which they tend to settle in the calyx, results in the rejection of such fruit for export, with a consequent monetary loss to tho grower. In the case of citrus varieties, the feeding activities of the insects cause the fruit and leaves to drop prematurely. They blemish grapes and render them unfit for the marEet. Characteristics of Pest The insects commonly recognised as mealy-bugs are the females, which are wingless. In a colony of the insects will be found numerous small narrow cocoons, in each of which lies a developing male. The latter when mature differs markedly from the female. It is very minute, possesses a pair of wings and has no mouth parts. It is therefore readily overlooked. In most cases the young mealy-bugs hatch from eggs laid by the mature female, and the young insects differ but little from the parent except in size. At first, both sexes aro alike and it is not till, later on in their development that the males and females assume their characteristic differences. The life-histories of the several species present much in common. On deciduous trees the mealy-bugs pass the winter sheltering in crevices on the trunk or branches of the tree, while on evergreen trees they may remain on the foliage, particularly along the mid-ribs of the underside of the leaf during winter. These over-wintering insects may be already mature or they may be younger stages which will become mature when development commences in spring.

The mature female deposits her eggs in a loose cottony sac of waxy threads. The egg sacs are usually placed on the trunk or branches of the tree and in some sheltered location. As each female mealy-bug may deposit several hundred eggs, it is seen that tho numbers rff tho mealy-bug population are capable of rapid increase under favourable conditions of climate and freedom from natural enemies. Increase in Summer

The young mealy-bugs, on hatching from the eggs, make their way to the young shoots, the leaves, or the fruits where they settle clown and commence to-feed. The time required for the production of a generation from the time when the egg is laid until the mealybug becomes mature probably is about tAvo months during the summer. Thus, in addition to the generation which passes the winter on the tree, there are probably two or three generations during the summer. As the time required for development is shorter during the summer, the numbers of mealy-bugs increase rapidly and are ilnially most abundant in late summer and autumn. In New Zealand there are about a dozen native species of mealy-bugs, but in general these are of little economic importance, Mr. Miller remarks. It is the introduced species that are responsible for most of the serious infestations. The following species are of importance.

The Citrophilns mealy-bug is met with on grape vines and begonia in classLouses where it becomes epidemic if left uncontrolled; out of doors it infests apple and potato as well as ornamental plants. This species is characterised by the mealy covering beinji coarse aijd distributed unevenly, while the marginal fringe is short, its processes being comparatively stout, particularly the tail-ltke ones which are much shorter than the body. Egclaying occupies a period of about two weeks during which time from 894 to G79 egga are deposited by each female. Development to the adult is completed in about six weeks though this will vary with the climatic condition*. Jll California four generations have been noted during the year. Widely-distributed Species

The long-tailed mealy-bug is characterised by the long tail-like appendages of the female. It is a widely-dis-tributed species commonly met with under glass. In the warmer and moister parts of tho Dominion it occurs out of doors where its list of food plants is a lengthy one, including grape and passion vines, wistaria, fig, oleander, Pliormium, cineraria, begonia, apple, plum, palms, and ferns. Considerable injury may be caused by the insect when it occurs in dense masses 011 the underside of foliage, and upon young succulent growth. No eggs are produced by this Species. The young are born alive and their production lasts for a period of from two to three weeks at the rate of about 12 each day. The time taken to reach maturity varies according to climatic conditions, tho range being from one to three months. There are comparatively few generations a year out of doors, but there are several under glass.