MEALY-BUGS

Wanganui Chronicle, Volume 77, Issue 154, 2 July 1934, Page 3

MEALY-BUGS

CAWTHRON INSTITUTE WORK THEIR LIFE HISTORY AND CONTROL (By David Miller, I’h.D., M.Sc., F.8.5.N.Z., F.R.E.S., Assistant Director and Chief Entomologist, Cawthiou Institute). Mealy-bugs belong- to that vast assemblage ol 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; we find much the same method of leading adopted by blood-sucking insects such as the mosquito. Not only do meary-bugs and their relatives weaken the infested plants by draining the sap t but they also cause destruction of chlorophyll, interfere with the normal functioning of the stomata, and have a toxic influence upon the tissues; further, many serious plant diseases arc carried and spread by these sap-sucking meets, whilst the feeding punctures may give access to the spores of disease. The presence of sap-sucking insects is very often to be detected by the stickiness and blackened appealance of the infested planto; this is due to the insects excreting a sweet sticky substance

known as “honey-dew” which co J ’ lects on the foliage and branches whilst upon it grows a black sooty mould. This mould, apart from spoiling the appearance of plants and fruit, probably restricts respiration and pre

vents the leaves from fulfilling their function of building up food supplies for the plants. Mealy-bug Characters Alealy-bugs may be readily recognised by the characteristic white mealy substance of a waxy nature that covers and protects the oody; further, this powdery covering is developed as & fringe of leg-Hke processes at the sides, while those at the posterior end. of the body may be prolonged as tail like appendages of varying length m some species, or they may ne no longer than the marginal fringe in others. Meal-bugs tend to congregate m colonies and are commonly found attacking apple, near,.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 c-r 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 the giowciq m the case of citrus the feeding activities of the insects cause the fruit and leaves to drop prematurely; while ttiey blemish grapes and render the latter unlit for the market. The insects commonly recognised as mealy-bugs are the females, wnich 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 wnen mature

differs markedly from the female; H is very minute, possesses a pair of wings and has no mouth parts; it is therefore readily overlooked. On removing the white protecting covering from a female the body is found to be pinkish in colour, oval in outline, and varying in length, from one-eighth to one-quarter of an inch according tu- the species, while on the underside arc three pairs of minute legs. Life-History In most cases the young mealy-bugs hatch from eggs laid by the mature 'lemale, and the young insects differ but little from the parent except in size. At first, bulb sexes are 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 tiee, white on evergreen trees they may remain on the foliage, particularly affing the midribs of the underside of the leaf during winter. These overwintering insects may be already mature or they may be younger stages which will become mature when development commenccs 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 'mealybug may deposit several hundred eggs it°is seen that the numbers of the mealy-bug population are capable of rapid increase under favcuratiio conditions of climate and treeaoni from natural enemies. The young mealy bugs, on hatching from the eggs, make their way to the young snoots, the leaves, or the fruits, where they settle down and commence to feed. The time required for the production of a veneration from the time when t e egg is laid until the mealy-bug becomes mature probably taxes about two months during the suiur- r. thus, ni addition to the generation which passes the winter on the tree, there are probably two or three generations during the summer. As >e time required for development is porter auring the summer, the numbers of mealybugs increase rapidly and are usually most abundant in late summer and autumn. New Zealand Species In New Zealand we have about a dozen native species of mealy-bugs, but in general these are of little economic importance. It is the introduced species that are responsible I'or most cf the serious infestations. The following species are of importance. The Citrophilus mealy-bug is met with on grape vines and ocgonia m glass-houses, 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 meary covering being coarse and distributed unevenly, while the marginal fringe is snort its processes being comparatively stout, particularly the tail-Uke ones which are much shorter than the body. Ugglaying occupies a period of about two weeks, during which time from <»9l to 679 eggs are deposited by each female. Development to the adult is completed in about six weeks, though this will vary with the climatic conditions In California four generations have been noted during the year. The long-tailed mealy-bug is characterised by the long tail-like appendages of the female. It is a widely distributed species commonly met with under glass, where it infests almost any plant. In the warmer and moister parts of the Dominion it occurs out of doors, where its list of food plants is a lengthy one. including grape and passion vines, wistaria, fig. oleander. Phormium, cineraria, begonia, apple, plum, palms and fems. Considerable

injury may be caused by tnc insect when it occurs in dense masses on the under side of foliage, and upon young succulent growth. No eggs arc produced. by this species. Trie young are bc-rn alive and their production lasts for a period of from two to three weeks «t the rale of anout twelve each day. The time taken to reach maturity varies according to climatic conditions, the range being from one to three months. There are comparatively few generations a year out c-1 doors, but there are several under glass. The apple mealy-bugs belong to at least two species, one originating in America and the other in Japan. Both attack apple, pear and potato in New Zealand. 'The injury by these mealybugs is not severe in itself, but the presence of the insects on the fruit of apple and pear is responsible f° r quantities being rejected. These two mealy-bugs are very similar in appearance. They are c-f the sliort taiied type but differ ifom the mealy-bug in having the mealy covering evenly distributed over the body, while the marginal iringc is delicate and thread-like. The eggs hatch in from two to three weeks and the young migrate freely, reaching maturity from one to two months i*ter. In the open the winter is passed in the egg stage, but under glass or in mild climates activity among the different stages occurs ihroughout the year. Apart from apple and pear, these mealy-bugs have been recorded from many plants. Control Alealy-bugs are noted for their resistance to sprays, the mealy covering of wax giving an efficient protection, borne insecticides, however, have given some degree of control; these are dormant sprays of miscible and soluble oils, and carbolic acid and distillate emulsions which dissolve the protective covering and penetrate to the body of the insects and to their eggs. A most eifective means of control is by fumigation, but this can be carried out only under cover. The best fumigant » calcium cyanide v> hich, when exposed to the atmosphere, generates hydrocyanic acid gas; this gas is extreme]) poisonous to humans and great care is necessary in its use. Parasites Owing to the difficulty c-f controlling mealy-bugs by sprays or fumigants, reliance has been placed chiefly j>n biological methods of control. The different species of mealy-nugs are attacked by a large number c-i parasites and predators. Of tnesc the most important has been the Australian ladybird beetle, Cryptolaemus. in California where mealy-bug wa.* a serious pest of citrus, this beetle was bred continuously in special inseetaries and liberated every year in the infested areas. This method proved to give more effective control at smaller cost than by the use of sprays. The ladybird beetle was introduced into New Zealand by the Department of Agriculture as early as 1887 and became established in the warmer parts of the North Islands. Since that time several attempts have been made by the Department of Agriculture and'the Cawthron Institute to establish the beetle throughout New Zealand. These were unsuccessful and it appears that climatic conditions over the greater part of New Zealand are not favourable to the existence of this beetle. A number of other parasites and predators have been introduced at various times, but none of these appears to have established itself in the field. In California it was found that one species of mealy-bug—the Citrophilus mealy-bug—was not satisfactorily controlled by Cryptolaemus, and in 1927 an expedition was sent to Australia to

discover if the mealy-bug existed there and if there were any promimjig parasites. The Citrophilus niealy-nug wai found in Australia and the expedition was successful in obtaining several paiasitcs ami predators which were shipped to California. These insects we<e bred and distributed In Jurge numbers and by 1932 the Citrophilus mealy-bug was under satisfactory control. This control was attributed to two of the introduced parasites of which the most important Is said to bo Coccophagus, an internal parasite of the mealy-bug. The Citrophdus mealy-bug wai known to be present in New Zealand ami there is some justification for considering that this species is responsible for most of the mealy-bug damage on deciduous fruits. In 1928 an unsuccessful attempt was made by the Cawthron Institute to establish several mealy-bug parasites in Now Zealand. Th c material was supplied through the courtesy of the University of California Agricultural Experiment Station. Early in 1933 a second consignment of parasites was received from California, and with the fev/ insects which emerged a thriving colony of Coccophagus was started at the Institute. The size of this colony had increased sufficiently to enable a number of liberations of Coccophagus to be made in different parts of New Zealand during the 1933-34 season. In addition the parasite has been liberated in Samoa and the Cook Islands, where mealy-bug »s a pest of coconuts.