An Account of the Insects Noxious to Agriculture and Plants in New Zealand / The Scale Insects (Coccididae)

AN ACCOUNT

OF THE

INSECTS NOXIOUS TO AGRICULTURE AND PLANTS

IN

NEW ZEALAND.

THE SCALE-INSECTS
(COCCIDIDÆ).

By W. M. MASKELL, F.R.M.S.,
REGISTRAR OF THE UNIVERSITY OF NEW ZEALAND.

WELLINGTON:
BY AUTHORITY: GEO. DIDSBURY, GOVERNMENT PRINTER.
1887.

Mr. Maskell's Account of the Scale-Insects occurring in New Zealand is published by the State Forests and Agricultural Department, under the instructions of the Hon. John Ballance, Commissioner of State Forests.

Wellington, 31st March, 1887.

CONTENTS.

[PREFACE.]

The number and variety of the insect pests which live on the plants of New Zealand, whether native or introduced, and the damage which they frequently do, form the excuse for the appearance of this work. The descriptions of these insects in the Transactions of the New Zealand Institute, or in works published in Europe and America, are not easily accessible to the general reader, and are also much scattered and fragmentary. It was thought therefore that the time had arrived when the information which might be useful to gardeners and tree-growers, as well as to students, might be summarized and brought together in a compendious form, and the present volume is an attempt towards this.

In order to render this work complete a second volume is necessary, which should include the large number of other destructive insects preying upon various plants. For example, the "pine-blight" (Kermaphis), the "American blight" (Eriosoma), the "black leech" (Tenthredo), the cabbage caterpillar, the turnip "fly," the various aphides on roses, geraniums, &c., the grass-grub (Odontria), the codlin-moth, the borers, weevils, wireworms, and a number of others are in different places damaging trees and plants, and it would be useful to collect in one volume information regarding them. The author has had in contemplation the preparation of such a volume, and it is hoped that it may be at some future time published.

Meanwhile the present is offered as, at least as far as it goes, a full description of one of the most general as well as the most noxious families of plant-parasites. The plates have been especially prepared with a double object: first, that gardeners and tree-growers might be able easily to recognize the kind of insect which might happen to be damaging their plants; and, secondly, that the student who should desire to know more of this curious family might have enough details indicated to guide him in his investigation. For the first purpose the figures have been coloured as near to nature as possible; for the second a few anatomical details have been introduced. The printing of these plates has been executed by Mr. Potts, lithographer to Mr. A. Willis, of Wanganui, and it is hoped that the reader may be well satisfied with the care and trouble which have been bestowed upon them.

The author is sensible that this volume may contain numerous imperfections; but these will not, he trusts, be attributed to culpable ignorance or carelessness.

[EXPLANATION OF TERMS USED IN THE FOLLOWING PAGES.]

Abdomen. The posterior half of the body of male or female, whether joined to the anterior half or slightly separated, segmented or not.

Abdominal cleft. A narrow slit in the extremity of the abdomen of Lecanidinæ and the full-grown Hemicoccidinæ only. ([Plate IX.], Fig. 1, b, c.) On the upper side of the body are seen the

Abdominal lobes, two minute, divergent, triangular or conical, excrescences, one on each side of the cleft, in Lecanidinæ, usually bearing one or more hairs. ([Plate XI.], Fig. 3, b, c.)

Abdominal spike. A more or less long, tubular or semi-tubular, pointed process terminating the abdomen of the male in all species, and serving as a sheath for the penis, which is a long, white, soft tube with recurved hairs. ([Plate II.], Fig. 3; [XXI], Fig. 1, k.)

Anal ring, anogenital ring. An orifice situated near the abdominal extremity of the female, either simple or compound, hairless or bearing several hairs. ([Plate II.], Fig. 1.)

Anal tubercles. Exhibited only by the Coccidinæ and by the larvæ of Hemicoccidinæ: two more or less conspicuous projecting processes at the abdominal extremity of the female, without any cleft, and in most instances projecting beyond the edge; usually bearing setæ. ([Plate II.], Fig. 2, c, d.)

Antennæ. Two jointed organs ("feelers") projecting from the anterior portion of the body, of variable length. ([Plate I.], Figs. 9, 10, 11, types.)

Apodous. Without feet.

Apterous. Without wings.

Bucca, buccal. The mouth; belonging to the mouth.

Carina, carinated. A keel or raised-ridge; keeled.

Cephalic region. That part of the insect, male or female, which bears the eyes, antennæ, and mouth, but not including the first pair of feet.

Clavate. Club-shaped; somewhat knobbed.

Claw. The hooked terminating joint of the foot. ([Plate I.], Fig. 6, cl., type.)

Coxa. The first joint of the foot, springing directly from the under-side of the thoracic region. ([Plate I.], Figs. 6 c, 7 c.)

Digitules. Appendages observed on the feet, and often useful for distinguishing species. Usually there are two pairs. The "upper pair" spring from the upper side of the extremity of the tarsus, and are generally long, fine hairs, terminating in a knob. The "lower pair" spring from the base of the claw, and are usually broader and more trumpet-shaped than the upper ones. ([Plate I.], Fig. 8, type.) Sometimes either pair, or both, may be absent. In Cœlostoma wairoense there are no "upper" digitules, and 24 "lower" ones on the foot of the male. ([Plate XXI])

Dimerous. Two-jointed.

Dorsum. The upper side of the body when the insect is in its natural position.

Dorsal. On the upper side or dorsum.

Eyes. Two coloured, granular or simple, round organs on the cephalic region of the female, near the base of the antennæ ([Plate XIV], Fig. 2, k.; Plate xx., b); two, or four, coloured, granular, simple or facetted, on the head of the male ([Plate I], Figs. 14, 15; [Plate XXI], Fig. 2, b).

Femur. The second joint of the feet, next the coxa, joined to it by the false joint "trochanter." ([Plate I], Figs. 6 f, 7 f.)

Fringe. A portion of the excreted substance, cotton or wax, produced by the spinnerets on the edge of the body in certain Lecanidinæ and Hemicoccidinæ. It may be in the form of long glassy threads (Planchonia) or of more or less broad flat plates (Ctenochiton). ([Plate VII], Figs. 2 d, 3 a; [Plate XII], Fig. 2, a, b, c.)

Haltere. A minute organ, situated just behind the wings of the males, and of which the use, either in this family or in the Diptera, has not been satisfactorily ascertained. It is often termed the "balancer." In the house-fly it has been thought to represent an organ of hearing. In Coccids it is furnished with one or more hooked bristles, and Mr. Comstock affirms that these are, probably for some purposes of flight, hooked into the posterior edges of the wings.[A] ([Plate I], Fig. 17; [Plate XXI], Fig. 1, m.)

[A] Report of the Entomologist, U.S. Dep. of Agric. 1880, p. 277, note.

Honeydew. A substance of a glutinous character produced by many species, and falling in spray from them on the leaves. (See Chap. III.)

Larva. The first stage in the insect's life after emerging from the egg.

Lobes, in the Diaspidinæ, are minute, flat, more or less rounded projections, two or more, seen on the edge of the abdominal extremity, usually interspersed with spines and hairs ([Plate III], Figs. 1, 3, 4, 5, l); in the Lecanidinæ, are two triangular or conical projections, usually bearing hairs, on the dorsal side of the body, one on each side of the abdominal cleft ([Plate XI], Fig. 3, b, c).

Mentum. A kind of secondary rostrum, or "under-lip," not altogether tubular, but rather a deepish trough, through which the rostral setæ pass after leaving the rostrum. It may have one, two, or three joints. It is not noticeable in the Diaspidinæ. ([Plate I], Fig. 5, b.)

Metamorphosis. A change of form. For the number and characters of these see Chap. II.

Moniliform. Like a string of beads.

Monomerous. With a single joint.

Multilocular. With several divisions: a term applied to the spinneret orifices of some insects, distinguishing them from "simple" orifices, which show only a single tube. Multilocular orifices exhibit a bundle of tubes enclosed together. ([Plate I], Fig. 4, c, d, p; [Plate XVIII], Fig. 2, e.)

Nervure. A strong vein which, starting from the attachment of the wing of the male, runs along the anterior edge of the wing, a little within it: at about half its length a branch runs obliquely towards the posterior edge. ([Plate I], 16; [Plate XIX], f; [Plate XXI])

Normal. According to rule—not exceptional.

Ocelli. Two, four, or six minute circular simple organs, on the head of the male: probably organs of vision. In the Monophlebidæ they would seem to be replaced by a smooth rounded protuberance behind the eye. (Plate i., Fig. 14, oc.; [Plate VIII], Fig. 2, k, m; [Plate XXI], Fig. 2, b.)

Ovisac. The cottony bag or nest formed by certain species of Lecanidinæ and Coccidinæ for the reception of their eggs. ([Plate XII], Fig. 1, a, b, c; [Plate XIX], a, b, c.)

Peduncle, pedunculated. A stalk; stalked.

Pellicle. The skin of an earlier stage, cast off at each metamorphosis; used by the Diaspidinæ and by one genus of Lecanidinæ in the formation of the puparium or test. ([Plate I], Fig. 3, a, b; [Plate VII], Fig. 2, b.)

Polymerous. Many-jointed.

Pupa. The last stage of the male insect before emerging winged.

Puparium. The shield, covering, or "scale" of the Diaspidinæ. ([Plate I], Fig. 3, e; Plates iv., v., vi.)

Rostral setæ. Three or, in a few cases, four long, fine, curling, tubular bristles springing from the rostrum, and often passing through a mentum; used for insertion into the tissues of a plant and sucking their contents. ([Plate I], Fig. 5; [Plate VI], only one being here shown, from the smallness of the drawings.)

Rostrum. A more or less conical, tubular, projecting organ, or beak, protruding from the under-side of the cephalic region, or between the first pair of feet. It is absent in the adult female Cœlostoma. It is the "mouth" of the insect. ([Plate I], Fig. 5; [Plate IV], Fig. 5.)

Sac. The cottony, bag-like covering or nest produced by the spinnerets and concealing the insect in many of the Coccidinæ and some Lecanidinæ. ([Plate XV], Fig. 1, c; Fig. 2, b.)

Scale. The shield or puparium of the Diaspidinæ. The word is commonly used to designate the outward appearance of insects of the whole family, which are indiscriminately called "scale-insects," although many of them form no shield whatever.

Secretion may be of various kinds. It is matter produced by internal organs, and expelled through the "spinnerets." In the Diaspidinæ the secreted portion of the puparium (that is, all except the pellicles) is made up of fine, closely-woven fibres, forming the "scale." In the Lecanidinæ it probably exudes originally as fine fibres, but these become agglomerated in some cases in a waxy or horny mass, or in others are loosely collected as cotton. In the Coccidinæ the secretion is usually cottony, or powdery like meal. Cœlostoma secretes all three—wax, cotton, and meal. In some instances, as in Carteria lacca, of Africa, the wax, called "shellac," is abundant enough to be commercially valuable; or, as in the Chinese Ericerus Pe-la it can be used for making candles.

Seta. A bristle—a long stiff hair.

Setose. Bearing a few bristles.

Spinnerets. Organs observed in various parts of the body, producing the waxy, cottony, or mealy matter. They consist of cylindrical internal tubes, sometimes ending on the skin, sometimes protruding outside it in the form of tubes, spines, or conical hairs. In the former case the orifices show them to be in some instances simple, and in others compound tubes.[B] In the Diaspidinæ, besides being scattered over the body, the spinnerets are arranged in groups on the last abdominal segment, and these groups afford excellent characters for specific distinctions. ([Plate I], Fig. 4, for types of various spinnerets; [Plate III], groups of spinnerets of Diaspidinæ.)

[B] Minute anatomical details are unsuitable for this work. The student may consult Targioni-Tozzetti, "Studie sulle Cocciniglie," cap. ii., p. 26.

Spiracles. "Breathing organs:" the orifices in the body of the tracheæ or tubes conveying air to the blood. In the Lecanidinæ they are usually four; simple circles, near the edge of the body, and with a few strong spiny hairs near them. In the Coccidinæ they are often numerous. ([Plate II], Fig. 4; [Plate XX], n.)

Spiracular spines. Spiny hairs, usually three in number, of which one is rather long, close to the spiracles, in the Lecanidinæ.

Stigma, stigmatic spines. Terms sometimes employed for spiracles, &c.

Tarsus. The fourth joint of the feet, between the tibia and the claw. Its consisting of one joint (monomerous) is a distinctive character of the whole family. ([Plate I], Fig. 6, ta.; Fig. 7, ta.)

Test. The waxy, glassy, or horny covering produced through the spinnerets and concealing the insect in many Lecanidinæ and some Coccidinæ. In this work it is not applied to the "scale" of Diaspidinæ or to cottony secretions.

Thoracic band. An appearance seen on the thoracic region in the male, looking like a broad transverse ribbon.

Thoracic region, thorax. That part of the female or the male which bears the three pairs of feet, when the feet are present; or, if the feet are absent, the middle portion of the body, segmented or not.

Tibia. The third joint of the feet, next the femur. ([Plate I], Fig. 6, ti.; Fig. 7, ti.)

Tracheæ. Tubes ramifying throughout the body, conveying air to the blood. Their orifices are the spiracles. The tracheæ, as in other insects, appear as if constructed of a network of fine spiral wires. ([Plate II], Fig. 4 d; Plate xx., n.)

Trochanter. A small articulation, not a distinct joint (something like a knee-cap) of the feet, between the coxa and the femur. ([Plate I], Fig. 6, tr.; Fig. 7, tr.)

Trimerous. Three-jointed.

Ventral. On the under-side, the insect being in its proper position.

[NEW ZEALAND SCALE-INSECTS]

(COCCIDIDÆ).

[CHAPTER I.]

INTRODUCTORY.

Insects are divided by naturalists into several principal orders, the distinguishing marks of which are generally very well defined—for example, the butterflies and moths belong to the order Lepidoptera, the dragon-flies to the Neuroptera, the common house-flies to the Diptera, and so on. These orders are founded upon the characters and arrangement of the wings. They are subdivided into families, and these again into genera and species. One of the orders is that of the Hemiptera, which is composed of the two following sections:—

Hemiptera-Heteroptera, including the bugs, water-beetles, &c.

Hemiptera-Homoptera, including the crickets, cuckoo-spits, plant-lice (Aphides), leaf-hoppers (Psyllids), scale-insects (Coccids), &c.

The insects treated of in this volume are therefore placed as follows:—

Class—Insecta.
Order—Hemiptera.
Section—Homoptera.
Family—Coccididæ.

The genera and species will be found in their places.

The common English name for this family—"scale-insects"—is not very appropriate. Some few of them have the appearance of small thin scales on leaves or twigs, but many have not. Nor are the German appellations—"gall-insekten" or "schild-lause"—more appropriate. Gardeners have given to some of them the name of "mealy-bug," which, although decidedly neither elegant nor euphonious, very fairly represents the character of that particular portion of the family.

The origin of the name "Coccididæ," or, as abbreviated often in this volume, "Coccids," is found in the old Greek word "[Greek: kokkos]," denoting a rich red dye, which was much admired by the Greeks and Romans, and which was procured from the insect now known as Kermes vermilio (the Coccus ilicis of Linnæus). When the cochineal insect was discovered in Mexico it soon overpowered all the others, producing commercial dyes, and from it has come the title "Coccid," now applied to the whole family. Cochineal itself has of late years been pushed aside to a great extent by the aniline (coal-tar) dyes; yet it is still used for many purposes. This insect lives on the leaves of cactus. Amongst the New Zealand species described in this work will be found one, Dactylopius alpinus, which produces a red dye similar to, though probably not equal to, cochineal. Before the discovery of aniline dyes it might possibly have been worth while to cultivate this insect for its dye; but this would scarcely answer now.

The Coccididæ are, in some parts of the world, very injurious to vegetation. They seem to affect principally the warmer temperate regions. California, Florida, the Cape of Good Hope, the southern parts of Australia, Southern France and Northern Italy, and New Zealand are countries in which they are found out-of-doors in the greatest numbers. In England they are less troublesome in the open air, though in greenhouses and hothouses they abound; but, in places under glass, every gardener ought to be able to get rid of them without difficulty. For its extent New Zealand seems to furnish a larger number than any other country. The humidity of its climate and the absence of anything like severe winters in most parts of it are quite congenial to Coccids; and there is scarcely a tree in its forests or in its gardens, whether native or introduced, which is not subject to their attacks.

It has not been thought necessary to include in this work a list of the books and essays written on this family of insects. The list would be a very long one; but, besides that many of the books would not be obtainable here, it would be found that very many authors have done nothing more than copy—often quite blindly and unintelligently—what others had said before them; moreover, most of them are out of date. The student or the horticulturist desiring to know more about Coccids not found in New Zealand may find full details in the reports of the Agricultural Department of the United States Government, in Dr. V. Signoret's "Essai sur les Cochenilles" (Paris), in papers by Miss Emily Smith (American naturalist, 1878-80), &c. The American Departmental Reports of Professors Riley and Comstock, Mr. Hubbard, and Mr. L. Howard contain most valuable information. English works on the subject are mostly fragmentary or inaccurate; but Mr. Douglas, of Lewisham, has lately begun to discuss the Coccids in England in a systematic manner, and probably before long others will follow suit. In India, Mr. T. W. Atkinson, of Calcutta, is studying the family.

Natural science in these days tends ever more and more towards specialization, and the boundaries of scientific classes, orders, families, &c., are becoming always more and more narrowed. The student can find his time quite sufficiently occupied nowadays in the thorough investigation of so (comparatively) small a portion of the animal kingdom as is presented by the Coccids of even only one country; and the present work may not be without value to future workers in this direction. To the farmer, the gardener, the fruit-grower, and the owner of pleasure-grounds it is believed that the following chapters will also supply information at the same time correct, intelligible, and useful.

[CHAPTER II.]

CHARACTERS, LIFE-HISTORY, AND METAMORPHOSES OF THE COCCIDIDÆ.

The first principal character separating the Coccididæ from the rest of the Homoptera, and distinguishable without microscopic examination, is the absence of wings in the females at all stages of their existence.

The second principal character is the absence of any apparatus for feeding and digesting in the males.

From these two characters it follows that the females can only extend their operations by, at the best, crawling from plant to plant, or by being carried about by birds or other agency; also that the males cannot enjoy more than a very short existence, their work being entirely confined to impregnating the females. Hence, in any endeavours to destroy these insects, the males may be disregarded, and the females only attended to.

Other distinguishing characters, chiefly microscopic, are—

1. The presence of only one joint in the tarsus or fourth joint of the leg, in both males and females ([Plate I.], Figs. 6 and 7, ta);

2. The presence of only a single claw terminating the leg in both males and females ([Plate I.], Figs. 6 and 7);

3. The presence of only two wings, with two halteres, in the full-grown males ([Plate XXI.]);

4. The presence of two or more eyes or ocular tubercles, in addition to the ordinary pair of eyes, in the full-grown males ([Plate I.], Fig. 14; [Plate VIII.], Fig. 1, k, m).

I. The Female Insect.

In general outward appearance the female insects present very variable forms. They may be either naked, or covered over with some kind of a shield, which may be fibrous, or waxy, or cottony, or they may have simply a thin powdery meal scattered over them. The covered insects are, of course, stationary, although in some cases, before reaching their full development, they move about, carrying their houses with them. The naked insects may be either stationary or active.

They attach themselves either to the bark or stem of a plant or to the leaves. In the latter case it is rare to find them on the upper side; but, on turning over a leaf, the under-surface is frequently found covered thickly with them.

In many cases they exude, in the form of minute globules, a whitish, thick, gummy secretion, answering probably to the "honeydew" of the Aphididæ. This secretion drops from them on to the plant, and from it grows a black fungus, which soon gives an unsightly appearance to the plant. This fungus or "smut" is an almost invariable indication that a plant is attacked by insects,[C] and may, indeed, give a useful warning to tree-growers. It is not, however, produced in appreciable quantities by all species.

[C] Not necessarily a Coccid insect: the fungus may also grow on the honeydew of Aphis; but it is easy to recognize the difference between these insects. In every case there is some insect at work where the fungus is.

The manner of feeding upon the plant is the same as in all the families of Homoptera—namely, by means of a protruding rostrum, beak, or trunk, situated on the under-side of the insect. As there is not, in the female Coccididæ, any well-defined division between the head and the rest of the body, this rostrum is seen, on turning over the insect, in the form, usually, of a minute conical projection between, or nearly between, the first pair of legs, if the legs are present, or a little within the circumference, if the legs are absent ([Plate I.], Fig. 5). An ordinary lens will generally show, springing from the point of the conical rostrum, three or four longish, very fine, curling bristles. These bristles are, in fact, hollow tubes, and the insect, inserting them into the leaf or bark of the plant, sucks through them its food. It is thus plain that, with often great numbers of scale-insects sucking at it—pumping, as it were, its life-blood through their rostra—a plant must of necessity suffer greatly.

Birds do not, as a rule, seem to care much about eating the Coccididæ, whose work is thus little interfered with by them. The "white-eye" (Zosterops) or "blight-bird" has been seen feeding on scale-insects; but its visits are few and far between, and its assistance to the gardener in this respect not great. The Coccididæ are, however, much subject to attacks from Hymenopterous parasites, of which some account will be found in a subsequent chapter ([Chap. IV.]).

The effects of the Coccididæ are not confined altogether to damage to plants: there are some species producing materials useful to man. For example, Coccus cacti produces cochineal; Carteria lacca produces shellac; Ericerus pé-la is used by the Chinese for candles: and others might be mentioned. But, so far, no New Zealand species appears to be of any commercial use. Dactylopius alpinus makes a rather rich red dye in alcohol; Cælostoma zealandicum constructs thick, waxy coverings, which might possibly be turned to some account; but even these are probably not worth much.

Groups.

The groups into which the Coccididæ are, in this work, divided are as follow:—

1. Female insects constructing for themselves shields composed partly of secretion, partly of the pellicles discarded from earlier stages; abdomen not cleft; legs lost at full growth.

[Diaspidinæ.]

2. Female insects naked, or covered with shields of secretion, either waxy, horny, cottony, or felted; abdomen in all stages cleft; legs either lost or retained at full growth.

[Lecanidinæ.]

3. Female insects naked, or covered with shields of waxy secretion; abdomen of larva ending in prominent processes, abdomen of adult cleft; legs either lost or retained at full growth.

[Hemicoccidinæ.]

4. Female insects naked, or covered with secretion either waxy, cottony, or felted; abdomen in all stages ending in prominent processes; legs either lost or retained at full growth.

[Coccidinæ.]

Life-history.

The life-history of the insects in the above groups is as follows:—

All of them pass through four stages of existence: 1, the egg; 2, the young larva; 3, the second stage of life, or "pupa;" 4, the adult, or full-grown insect.

1. The egg. This is, in all cases, of regularly-oval form, the colour varying from white to yellow or red (see [Plate i], Fig. 1). It may be produced in great numbers, and in some cases several times in a year. As a general rule, the female ejects the eggs from her body; but there are some species, notably in the group Lecanidinæ, where the eggs are hatched within the body, the insect being thus, in a manner, viviparous.

2. The young larva ([Plate I.], Fig. 2). This is of precisely the same form both for the male and the female—or, rather, perhaps it should be said that no definite character has yet been discovered to show which are male and which are female larvæ. Neglecting slight variations of form, the larva is very minute—seldom more than about ¹/₃₀ in. long, often as small as ¹/₁₀₀ in.—oval, flattish, possessing a rostrum and accompanying bristles (setæ), six legs, and two antennæ: and in all species it is fairly active, travelling as soon as hatched over the plant in search of food.

3. The second stage. Here the first distinction is noticeable between the male and the female in most cases; but this distinction usually depends not so much upon the form of the insect as upon the character of the covering it makes for itself. Confining ourselves at present to the female, there are differences now noticeable between the groups. In the Diaspidinæ the insect begins by slipping out of the skin of the larva; but it does not cast it aside altogether: it makes use of the old skin as part of its covering. Adding to it a small portion of fibrous secretion—produced by organs called "spinnerets," which will be noticed presently—it attaches itself to the plant by its rostrum and setæ, and lies, inert and stationary, under a little shield composed half of its old skin and half of secretion. As it also, in entering this stage, loses its legs altogether, it must remain in the position it has chosen for the rest of its life. In the Lecanidinæ and in the Coccidinæ the skin of the larva is thrown away altogether, and the female in her second stage takes up a new position, in which she may be either naked or covered with a thin coat of secretion, active or stationary, retaining her legs in most cases, or losing them in some instances. In all the groups there is almost always some approach to the form of the full-grown insect noticeable in this second stage.

4. The full-grown insect. Here there is almost unlimited variety of form, colour, and habits. The insects may be naked or covered, active or stationary. In the Diaspidinæ the process just described is repeated: the female slips out of her second skin, but still keeps both it and the first over her, adding more fibrous secretion from the spinnerets; so that, in fact, she lies an inert, legless, slug-like object, under a covering composed partly of the two skins, partly of secretion. (See [Plate I.], Fig. 3: a is the discarded larval skin, b the discarded skin of the second stage, both being used as part of the shield. In the genus Aspidiotus these skins would be in the centre instead of at one end.) In the Lecanidinæ (except in one single genus) and the Coccidinæ the second skin is discarded altogether; but the insect may either construct a new shield or remain naked, may be either with or without legs, either active or stationary. Once this last stage of her existence entered upon, the female prepares for laying her eggs. In most species the services of a male are needed; in some, as far as can be made out after investigation of many years, no males are found. The female, if naked, either hatches her eggs in her own body or lays them on the plant; if covered, she fills her shield with the eggs. The naked insects often cover the eggs themselves—e.g., Lecanium hemisphæricum; or, again, deposit them in an ovisac, a mass of cottony secretion—e.g., Pulvinaria camellicola or Icerya purchasi.

II. The Male Insect.

It has been remarked above that, as the full-grown males of the Coccididæ are destitute of any organs for feeding whatsoever, there is no reason for making systematic attacks on them for economical purposes. Their function is simply to impregnate the females, and their life at this stage must necessarily be very brief. It will suffice in this place to observe that in all cases these males are small, two-winged flies, their size varying from about ¹/₄₀ in. to ¹/₄ in. in length; colour usually yellow or red; wings longer than the body, hyaline (glassy) and often iridescent, and, in repose, lying flat, partly crossing each other. The antennæ are long, slender, and hairy, consisting of nine or ten joints. The legs are also slender and hairy, the tarsus having only one joint, and terminating in a single claw. The insects are generally very active. Types of antenna, foot, wing and haltere, and a diagram of the arrangement of the eyes and ocelli, are given in [Plate I.], Figs. 7, 12, 13, 14, 15, 17.

The males are thus so small and rapid in their movements that it is difficult in most cases to find them in a free state. The usual way to procure them is by hatching them from the pupæ. In their course of life they pass through four stages, as do the females—viz.: 1, the egg; 2, the larva; 3, the pupa; 4, the full-grown insect.

1. The egg is, as far as can be made out, precisely the same as that of the female, though Dr. Signoret believes that in one or two species there may perhaps be minute differences.

2. The larva is, as stated above, similar to that of the female.

3. The pupa. Here the first distinctions between the sexes may be noted, and these are principally observable in the cocoons or puparia, rather than in the insect itself—at least to outward appearance. The male pupa is, in all cases—even in those where the female pupa is naked—enclosed in some kind of covering. In the Diaspidinæ the puparium is formed partly of fibrous secretion and partly of discarded skin; only, as the full-grown male emerges from it as a fly, and does not remain on the plant, there can be only one such skin—that of the larva; consequently it is easy to distinguish the male puparia from the shields of the adult females by the presence of only one discarded pellicle instead of two. In the Lecanidinæ and the Coccidinæ the male puparia are distinguishable usually by a narrower and more cylindrical form than those of the females, where these latter are covered; in the naked species the males are generally in white waxy or cottony cocoons.

Examination of the pupæ in these coverings will generally show more or less developed processes on the back and sides, which are so evidently the rudiments of the future wings that the presence of a male is not doubtful. In other respects the male pupæ are not always to be distinguished from the females.

3. The full-grown male has been described above. It is usually easy to procure specimens, provided the pupæ are obtained. If any of these, in their coverings, are put into pillboxes with glass tops, or any place where light reaches them, they will generally produce the full-grown insect sometimes in a few days, sometimes after several weeks. The time of year for this seems very variable. Males emerge from the puparia apparently indifferently (in New Zealand) in summer or winter.

[CHAPTER III.]

PRODUCTS OF THE COCCIDIDÆ.

[Waxy or cottony matter: the "honeydew" and the black fungus—"smut" or "black blight"—growing upon it.]

The Coccididæ, in some parts of the world, excrete various substances which are of commercial value, as, for example, shellac, "manna," candle-wax, &c. Cochineal is not in the same category, as it appears to be a colouring-matter pervading every cell of the tissues of the insect from which it is extracted—Coccus cacti. But there is no need to dwell here upon the ordinary excretions of the New Zealand insects, as they appear to be not sufficient either in quantity or quality for any practical service. The fibrous puparia of the Diaspidinæ appear to be quite useless. The tests of the Lecanodiaspidæ, such as Ctenochiton perforatus, Inglisia ornata, &c., although more or less waxy (but of very brittle material, often more like glass) are much too insignificant to repay any trouble taken to collect them. Of all the family, Cælostoma zælandicum, in its second stage, seems to produce the greatest amount of material, its large, hard, waxy tests being very thick and solid, and often clustered in hundreds on a root or a twig of Muhlenbeckia; but, supposing this substance (of which the true chemical nature[D] is not yet known) to be fit for some purpose, there does not seem to be any means of cultivating the insect to profit. Dactylopius alpinus produces in alcohol a rich red tint, and this not by way of excretion, but from the colouring matters of its tissues, as in the case of Coccus cacti; but here, again, the rarity of the insect and its out-of-the-way habitat would be a bar, even if nowadays it were worth while to cultivate a New Zealand cochineal. At present, therefore, there seems no reason to believe that the Coccididæ of this country are likely to furnish any products of a useful or commercial character.

[D] A small quantity was submitted to Mr. Skey, Colonial Museum Laboratory, for analysis, no more being available at the time. Mr. Skey considered it as a new substance, probably of the nature of a gum, not resinous; but further examination of larger quantities is necessary.

There is, however, one substance produced by these insects which has an injurious effect upon the plants they grow on. This is a transparent glutinous fluid, apparently analogous to that exuding from Aphides, and which may receive the name of "honeydew," as in that family. In fact, this fluid would seem to be produced by most of the Rhynchota, for the Psyllidæ and Aleurodidæ also excrete it. The quantity issuing from Coccids seems to vary greatly. In some cases—e.g., Lecanium hesperidum, Ctenochiton viridis or perforatus, Fiorinia asteliæ—the insects appear to discharge "honeydew" freely; in others—e.g., Mytilaspis pomorum, Rhizococcus fossor—none, or scarcely any fluid, is excreted. But in no case does it appear that our Coccids[E] form honeydew to the same extent as the Aphides, which are stated to produce sometimes quantities that may be gathered from the leaves or the soil by the pound weight. It is not so much the amount exuding from each insect as the great number of insects on a plant which renders the Coccid honeydew obnoxious: each individual may excrete only a little, but when, as usually happens, there are many hundreds of individuals together, the result, for the reasons given below, becomes important to the tree.

[E] Gossyparia mannipara, an Arabian Coccid, is said to excrete so much that the Arabs "eat it with their bread like honey." Buckton, "Brit. Aphides," Vol. I., p. 42.

There is every reason to believe that the honeydew of Coccididæ is of similar character to that of the Aphididæ, and, according to analyses by Boussingault, of Paris, and Gunning, of Amsterdam (Buckton, "Brit. Aphides," Vol. I., pp. 42, 43), the Aphidian honeydew contains a very large quantity of sugar, and, curiously enough, cane-sugar. Some observers, noticing in its composition also glucose and dextrine, have considered it as of vegetable rather than animal origin; but the weight of evidence appears to make it certainly the product of the Aphides. As the present work is intended rather as a manual for gardeners and tree-growers than as a purely scientific publication, there is no need to enter more fully into the subject here: it may therefore be simply stated that the honeydew of Coccididæ probably contains a large proportion of sugar in various forms.

The mode in which this substance is excreted by the insects differs somewhat from that of the Aphididæ. On the abdomen of Aphis are seen two erect more or less prominent tubes, called "cornicles" or "nectaries," and it is the function of these to excrete the honeydew.[F] No European entomologist has, it is believed, seen or described the organ of honeydew-excretion in the Coccididæ. Some observations by the author of this work in 1886 demonstrate its existence as a cylindrical tube exserted from the anogenital orifice after the manner of a telescope, the furthest-extended tube being the most slender. This organ, extremely difficult of detection when not in use—except in the single genus Cœlostoma—is at intervals pushed out to its full extent, and at its further extremity there appears a minute globule of yellowish, nearly transparent, glutinous fluid, which rapidly expands like a soap-bubble, and then, suddenly breaking, falls in spray on the leaf beneath. In the second stage of the female of Cœlostoma zælandicum this organ may be detected more easily than in any other Coccid; but the act of protrusion of the organ and the formation of the drop of honeydew are apparently by no means frequent, and many long observations may be made without witnessing either.[G] (The organ and the honeydew-drop are shown in [Plate xxii])

[F] The fluid also emerges from the anal orifice; but, seemingly, no mention is made by any observer of any special honeydew-organ protruding from the anus of Aphis.

[G] Mr. Comstock ("Report on Insects," U.S. Dept. of Agric., 1881, p. 22) states that on gently rubbing a Dactylopius two small drops of fluid, which he considers to be honeydew, can be seen to emerge from orifices on the dorsal side of the sixth abdominal segment; but he mentions no special organ in the body. The experiment has been tried on Dactylopius in this country without success.

For the purposes of this work further details as to the production of honeydew are not necessary. But as to its effect on plants it is requisite to be more particular, and the attention of tree-growers and gardeners is specially directed to the following points. It has been said above that when the bubble of honeydew has been expanded to its full size it breaks into spray. Now, as a general rule, Coccids are found almost exclusively on the under sides of leaves (when not on the bark). Some, as Lecanium hesperidum and a few others, may be seen on the upper side; but the general rule is as here stated. It follows that the spray of honeydew from the burst bubble falls, not on the leaf where the insect is, but on the upper sides of the leaves below it. These upper surfaces, being more exposed to light and air than the lower ones, are usually deserted not only by the Coccids but by other insects also, and so there is not much chance that the honeydew spray so falling will be disturbed. It consequently rapidly accumulates and forms a coating on the leaf where it rests. From this result two things, or, rather, the same injurious effect on the plant is produced in two ways. First, the honeydew itself, being, as stated, of a glutinous nature, tends to stop up and choke the stomata (or, in plain English, the breathing-orifices of the leaves) and so retard the growth of the tree. Secondly, the honeydew, being of a saccharine nature, is especially attractive to fungoid growths, and these fungi, rapidly increasing, tend still more to choke the leaves and hamper the proper functions of the tree.

The second of these is the most important, for, apparently, the honeydew is scarcely deposited before it becomes the receptacle for fungus-spores, and these grow with great rapidity. As a general rule, in New Zealand, these fungi appear to be mostly of the same family—the Physomycetes, and they are of a black or very dark brown colour. From the fact above stated, that the honeydew falls from the insects upon leaves beneath them, the lower leaves of a plant are more covered with it than the upper ones: these black fungi consequently discolour chiefly the lower leaves and branches; often the uppermost branches are nearly free from them. But the effect produced on the tree is not only unsightly, from the sooty blackness, but also injurious, from the choking-up of the stomata both by the honeydew and the fungus. As for ornamental plants, whether under glass or in the open air, the black coating is quite sufficient to spoil them.

These fungi are of various species, and specimens are given here in [Plate xxii]: on the leaves they form usually a hard, thin, black coat; while on the twigs and stem they are of a looser texture, forming masses of minute erect threads. They are not confined to New Zealand, and most writers on Coccididæ in Europe and elsewhere mention them, though only casually. They are, in fact, apparently, only the usual growths appearing on any decomposing substance, such as the honeydew is.

Gardeners and tree-growers ought to clearly understand that the appearance on their plants of this black sooty covering is almost always an indication of the presence of some Homopterous insects. In New Zealand, on account of the greater prevalence of Coccididæ, the insects will most probably be Coccids; but by no means necessarily so, for many Aphididæ, Psyllidæ, and Aleurodidæ produce the same effects. This is by no means as well understood as it should be, either by gardeners themselves or by those who write on trees and planting. The fungus growth is usually imagined to be in itself a disease of the plant, and efforts are made for its treatment without regard to its real origin, the insects on the leaves or bark. Under the names of "smut," "black blight," &c., it is often referred to as a destructive pest; and remedies are suggested which can, of course, have no permanent effect unless they are equally efficacious against the insect producing the honeydew. It is probably from this cause that sulphur, which is an excellent remedy against fungus, has been so great a favourite with those who pretend to have discovered what are called "scaly-blight destroyers;" and gardeners, seeing, perhaps, these nostrums clean some of the fungus from their trees, are under the false impression that the "scale" is also cleared away. The truth is, that the real remedy against "black blight" is to kill the insects on whose excreta it flourishes, if that can be done. As to the modes of doing this see Chapter V.

It is not, of course, pretended here that fungi of different kinds, and even those specially referred to, will not grow independently of insects and honeydew; and trees are, undoubtedly, subject to fungoid diseases which are not to be traced to any animal action. Still, the rule holds good; and the first effort of a gardener on the appearance of black blight on his plants should be to discover the insects on its leaves or bark, and deal directly with them. Once they are destroyed the fungus growth will in a short time disappear.

[CHAPTER IV.]

CHECKS TO INCREASE OF COCCIDIDÆ, PARASITES, ETC.

The Coccididæ, like all Homoptera, produce great numbers of young; but their increase does not appear to be as rapid as that of some other families. The numbers of some Aphididæ or Aleurodidæ produced from a single female in the course of a single year have been calculated at hundreds of thousands, if not millions; and as many as eleven generations have been produced in little over half a year. Coccids, however, as a rule, do not propagate at this alarming rate. Many, if not the great majority of them, produce in this country but one generation in the year, e.g., Mytilaspis pomorum, Cœlostoma zælandicum, &c. Others, such as Icerya purchasi, breed more often; and probably climate has a good deal to do with the frequency, for Mr. Comstock says that in the United States Mytilaspis pomorum breeds once a year in the North and twice in the South. In point of fact, it does not seem possible to lay down any rule on the subject. Unfortunately, Icerya is not only a frequent breeder, but also the most destructive insect of the family in New Zealand.

The number of young produced by each female seems also to vary. The author has counted from 30 to 80 eggs in the puparium of Mytilaspis pomorum; as many as 350 in the ovisac of Icerya purchasi, and about the same number of Cœlostoma zælandicum: and a female of Lecanium hesperidum examined in spring contained 93 embryos. These figures do not denote any remarkable fertility; but, as in the majority of cases males are but seldom met with, sometimes even entirely unknown (e.g., Lecanium hesperidum), it follows that nearly every insect is capable of propagation, and the increase in numbers is therefore more rapid than might be anticipated otherwise. How the females in the species apparently destitute of males are enabled to produce young is perhaps one of the most mysterious things in Nature. The male of Mytilaspis pomorum has never been found in New Zealand or Europe, and doubtfully in America. Lecanium hesperidum has been known and studied for nearly two hundred years without any male, pupa or adult, being discovered. Yet both of these species go on increasing regularly and in great numbers, and show no signs of extinction.

In spite of this absence of males in some cases, and of the comparatively small numbers of eggs, Coccids would naturally increase at an exceedingly rapid rate if left undisturbed, on account of the great proportion of females. They are, moreover, protected, to a great extent—First, by the fact that birds do not, as a rule, care to eat them. The "blight-bird" or "white-eye," Zosterops lateralis, has been noticed in this country pecking about in holly-hedges infested by Lecanium hesperidum; but it is not absolutely certain whether it was eating the Coccids or the other more easily picked-off insects on the plant, such as Psocus, which is very commonly observed among Coccids. And other birds seem not to devour them at all. Secondly, the usual position of these insects, on the under side of the leaves, or in the crevices of bark, is a great shelter and protection for them against birds or ordinary accidents. Again, they are in many cases effectually covered by the waxy or fibrous shields, or by the masses of cotton with which they surround themselves. In countries like the South of France, California, or the greater part of New Zealand, the winters do not appear to be sufficiently severe to injure Coccids, and many of them breed as much in winter as they do in summer. It would therefore seem that everything combines to assist these insects in their career, and in their propagation. Nature, however, has provided a check which is to some extent effective, at least against several species, although, unhappily, against some of the most noxious—such as Mytilaspis pomorum, the Dactylopii (mealy bugs), Icerya purchasi, &c.—it is not energetic in this country; and this remedy is the attacks of other minute animals, whether by direct devouring of the Coccids or by parasitism.

Direct attacks from animal enemies are not frequent. Whether from some inherent distastefulness, or from the difficulty of getting at them, Coccids are scarcely subject to being directly devoured. There are a few exceptions. Under the puparia of Mytilaspis pomorum a minute white Acarus (mite) may often be found, and it is noticeable that where it abounds the eggs of the Coccid are often shrivelled or empty. It is not improbable that this Acarus may feed on the eggs. It appears to belong to the genus Tyroglyphus, a mite which is not usually carnivorous; but Mr. A. Michael, an authority on mites, seems to be uncertain whether Tyroglyphus may not make a meal of the Coccid.[H] No others amongst the Diaspidinæ appear to be directly attacked, nor any of the Lecanidinæ; but amongst a number of Dactylopius glaucus on a leaf there may often be seen a minute caterpillar, apparently covered with many tufts of hair. This is the larva of the common ladybird (Coccinella), a beetle which, in both the larval and perfect states, feeds on Aphides, Coccids, and other insects. The larva may sometimes be seen holding a Dactylopius in its powerful jaws and devouring it. Another larva, smooth and without hairs, performs the same functions—it is the young of a small dipterous fly, apparently one of the Syrphidæ, insects also predatory; but this seems to be rare. In America, similar larvæ are said to feed upon the "black scale" (Lecanium oleæ). In this country, as far as is yet known, Lecanidæ are not directly attacked by the ladybirds.

[H] Quart. Journ. Royal Micros. Soc., Feb., 1885.

But this direct warfare by other animals is of small consequence. A more important check on the increase of many Coccids is afforded by the indirect action of minute hymenopterous insects, which make use of them as receptacles for their eggs. This plan is adopted by several Hymenoptera, of the families Chalcididæ, Ichneumonidæ, Proctotrupidæ, &c. They do not devour their prey; they allow it to live that they may live on it. By means of their long ovipositor they pierce its body, and deposit in it an egg. As the victim grows the egg matures, changes into a larva, and still remains in the body of the Coccid; changes again into a pupa, and by this time the Coccid is at liberty to die, for the parasite has no further use for it except as a shelter; then, when the proper time arrives, the perfect fly emerges and departs. All Coccids are by no means equally subject to this system. In the United States, according to Mr. L. O. Howard,[I] parasites are found in nearly all genera—Diaspidinæ, Lecanidinæ, or Coccidinæ. In this country, as far as observation shows at present, the Lecanidinæ are the most liable to attack, some of the Diaspidinæ next, and the Coccidinæ least of all. Mytilaspis pomorum, so hurtful to apple-trees, does not seem to be attacked. Icerya purchasi, the worst species of all, has not yet furnished a single parasitic fly. A few specimens of Dactylopius glaucus contain parasites; a good many of Fiorinia asteliæ and F. stricta; while Ctenochiton perforatus and C. viridis appear to be the favourite victims, as sometimes scarcely any specimens on a plant can be examined which do not contain either a larva or a pupa of a parasite. It is to be observed that in no case is more than one parasite to be found in a Coccid.

[I] Report of the Entomologist, U.S. Dep. of Agric., 1880, pp. 350-371.

Unfortunately, although this provision of Nature must have a very considerable effect in preventing the increase of Coccididæ, it is subject to two drawbacks. In the first place, as just observed, some of the most injurious pests appear to be unaffected by it. Probably, up to the present time the worst plant-enemies[J] in New Zealand have been Mytilaspis pomorum, Aspidiotus coccineus, Aspidiotus camelliæ, Lecanium hesperidum, Lecanium oleæ, Lecanium hemisphæricum, Pulvinaria camellicola, and Icerya purchasi. Here reference is made not so much to insects which render plants unsightly as to those which seriously injure its growth: many others, such as Fiorinia asteliæ or Ctenochiton viridis are ugly enough, but have not been destructive. Of the injurious species above named none, apparently, are troubled in this country by parasitic insects up to the present time, at least to any appreciable extent.

[J] Speaking of Coccids only; Kermaphis pini is equally, if not more, destructive.

A sketch of Ctenochiton enclosing a parasitic pupa, and of the perfect fly, will be found in [Plate xxiii] In a work like this the generic and specific characters of these parasites need not be given: they do not seem to differ much from hymenopterous and dipterous insects of other countries.

Another mode by which the too rapid increase of Coccids is checked is by the attacks of vegetable parasites—fungoid growths which permeate the whole body of the insect, and soon kill it. As far as experience in New Zealand extends as yet the genera Ctenochiton, Lecanium, and probably Eriochiton are the only ones so attacked. On certain plants in the forests, notably Hedycarya and Coprosma, circular spots may be commonly found on the under side of the leaves: some dark-brown, somewhat convex, some bright yellow and often quite globular. In spring, examination of a young larva of Ctenochiton viridis—a species very common on the above plants—will frequently show, either within the insect, or on its waxy test, or between the test and the insect, minute specks, which under a high power of the microscope, prove to resemble the filaments composing the brown or the yellow spots just mentioned. On turning over one of the brown fungi, or on pulling it to pieces, the dead body of a young Ctenochiton or Lecanium larva will always be found in the middle. Apparently this brown fungus does not attack any but young larvæ; but the bright yellow fungus will be found filling the bodies also of the females in the second stage, and the globular portion of the fungus will stand out above them. These fungi are not of the same genus as Empusa, the fungus which so frequently kills the house-fly; but they seem to act in much the same way within the insect.

Probably a good many of the Lecanodiaspidæ are preyed on and destroyed by these fungoid parasites, of which figures are given in [Plate xxiii]

[CHAPTER V.]

REMEDIES AGAINST COCCIDIDÆ.

Many people are under the impression that scale-insects out-of-doors are not of much consequence. They are aware that in greenhouses and hothouses these insects are a trouble to gardeners, and that they probably injure flowering or fruit-bearing plants in such situations. But they imagine that in the open air, and on large well-grown trees, Coccids do no very great harm; or, if the trees are for a time injured, that recovery and health will come before long, and the pest will disappear. This is not the place in which to controvert this or any other opinion. A work professedly dealing with facts should be as free as possible from controversial discussion. Whatever, therefore, may be the grounds of the opinion just stated, or the reasons for rejecting it, it will be sufficient here to say that there seems to be nothing to lead to the belief that New Zealand is likely to be different from other countries in this respect. To institute a comparison, it would be manifestly absurd to include such countries as England, or Germany, or, on the other hand, India, or Central America, or North Australia—Firstly, because in the greater part, or at least in the northern parts, of Europe the winters are much more severe than in New Zealand, and almost certainly the great cold is injurious to such insects as Coccids. Secondly, because in tropical countries it seems that the too great heat is equally obnoxious to them; and, with the exception of a few species, tropical Coccids are comparatively harmless. But it is to the warmer temperate or the subtropical regions that we must look for comparison—regions where there is neither too scorching a summer nor too ice-bound a winter. And, for this purpose, we have only to take such lands as California, Florida, the South of France or Northern Italy, the Cape of Good Hope, the southern regions of Australia, &c. The experience of these is, that some species of Coccids do injure, in every way, whether as regards ornamental or commercial value, a number of trees and plants on which the people of the country depend largely for subsistence or profit. In the South of France the olive industry has been in some years greatly cut down. In Florida, California, Australia, the Cape of Good Hope, oranges and apples have been so damaged that the value of an orchard or a grove has been reduced sometimes by 80 per cent. It may be said, moreover, that even in tropical countries the attacks of scale-insects are often most damaging: in Mauritius the sugar-cane and in Ceylon the coffee plantations have suffered from their ravages. The experience of American fruit-growers is certainly not to be despised, and the fact that both in California and Florida the people strain every nerve to get rid of the insect pests on open-air trees would seem to be distinctly against the notion that these little enemies can be neglected with impunity.

Nor, indeed, can it be said that in New Zealand itself the attacks of scale-insects out-of-doors are harmless. Apple orchards throughout the country bear evidence to the contrary: lemon-groves can be seen about Auckland where, instead of the thousands of fruit formerly grown, a few stunted lemons are all that the withered trees afford; and nobody can glance round the plantations at Nelson or Napier without recognizing the devastating powers of a scale-insect (Icerya).

The opinion that Coccids are not likely to do much harm in the open air is therefore scarcely tenable, and it will be of use to inquire what remedies can be provided against them.

There is a point, however, to be noted at the outset, and it is, that in reality there is not, as far as is yet known, any certain remedy against scale-insects. Not that ingenuity and experiment have not succeeded in inventing plans and substances quite efficient in killing the insects when applied to them. It is easy enough to kill an insect when you can get at it, in most cases; but the problem in this instance is not only to kill individual insects, but to do more. What is wanted is to get rid of whole communities of them, and, at the same time, to prevent their eggs from hatching and a new brood coming forth. Many of those who profess to know all about destroying "scale"—especially if they belong to that class which prides itself upon being "practical men"—being generally quite ignorant of the habits and life-history of the insects, are satisfied when they have tried some rule-of-thumb plan which seems to kill most of the adult insects, not dreaming that they have left the eggs unharmed and ready to send forth a fresh swarm at hatching-time. There is another obstacle which often prevents success in eradicating "scale." This is the difficulty of making sure of the effects of any remedy. A plan which has answered well in one place will fail in another, and this, not only as regards different countries, but even in the same district for neighbouring gardens, or even for neighbouring trees in the same garden. Tree-growers must be prepared to find the very same remedy which has cleared their neighbours' trees fail for their own; and in this country the author has seen, in one and the same orchard, some trees quite cleared, while on others, treated in exactly a similar manner, the "scale" was scarcely injured.

It is from want of knowledge of this and the like points that persons who have tried various remedies recommended to them have complained of failure, and condemned both the remedy and their adviser, whilst really neither was in fault.

Nothing need be said here of carelessness or unskilfulness in applying a remedy, beyond the following instance: A person whose apple-trees were being very much damaged by Mytilaspis pomorum was advised to apply, by way of painting the trunks and branches, a mixture of kerosene and some other ingredient. In two or three months he found violent fault with his adviser, for he said every tree was dead or dying. On inquiry it was found that, from over-zeal or want of knowledge, he had applied the mixture as if painting a house, had used it much too strong, and, to make assurance doubly sure, had given his trees two good coats of the oil.

An intelligent appreciation of the life-history and habits of scale-insects is necessary to enable any one to select and apply, with a probability of success, a remedy, and the details given in Chapter I. of this work will be found useful for this purpose. It will be apparent from them that, without regarding the generic or specific characters of these insects, we may lay down a few general principles to start with, thus:—

I. Whatever damage is done is effected by the sucking of the juices of the plant through the rostrum of the insect. It follows from this that applications of any fluid to the tree externally, with the object of poisoning the insects in their feeding, would be useless, as their food is drawn from beneath the surface.

II. Neglecting entomological distinctions, we may divide the Coccididæ, roughly, into—

(a.) Insects attacking deciduous plants;

(b.) Insects attacking evergreen plants;
or, again,

(c.) Insects living usually on the bark;

(d.) Insects living usually on the leaves;

(e.) Insects living on both bark and leaves;
or, lastly,

(f.) Insects covered with hard shields or "scales;"

(g.) Insects covered with cotton;

(h.) Insects naked.

It will be clear that a different method will be required for destroying these different classes; but any one insect will belong to more than one class. Thus Mytilaspis pomorum, the apple-scale, belongs to (a), (c), and (f), and indeed may be placed also in (b), as such plants as hawthorns, which it attacks, are as bad as evergreens in the difficulty of reaching the insect on them; or, Lecanium hesperidum is in (a), (d), and (h); Lecanium oleæ in (a), (b), (e), and (h).

As far as regards the injurious species of Coccids it may usually be taken for granted that those infesting deciduous plants (class a) live chiefly on the bark (class c), and are either naked (class h) or covered with a hard scale (class f). If naked they are chiefly Lecanium; if covered, either Mytilaspis, Aspidiotus or Diaspis.

Icerya is exceptional, being omnivorous, feeding equally on bark or leaves, deciduous or evergreen plants; it belongs to every class except (f). Every method of destruction has therefore to be resorted to against it.

The treatment of a deciduous plant infested by Coccids is simple as to its method. For two reasons the dead winter-time must be chosen for it—first, because, the leaves being off, the whole plant can be easily got at; secondly, because the eggs of the insect have not yet been hatched, and the whole brood can be destroyed at once. The first operation should be the pruning of the tree, so as to reduce the labour required to a minimum. A brushing over all the trunk and branches with a good hard stiff brush and one of the liquid remedies given below is then often successful. Brushing with a dry brush is adopted by some persons; but, although this doubtless clears away a good many insects and scales, and may do the tree itself some good by cleaning off fungus-growths and incrustations, yet it necessarily fails to destroy all the eggs, and in consequence the work is only half done. Any one who wishes to extirpate Coccids must make certain that he has destroyed the eggs—a fact which is quite ignored by numbers of those who glibly talk of their own success, and blame the advice of others. The object being, therefore, twofold, the operation should be performed with a hard, stiff brush dipped in one of the fluids recommended below; and care should be taken that there is no part of the trunk or branches escaping untouched. In fact, what should be aimed at is a kind of painting of the tree, but with a thin coating of the fluid, so as to close the pores as little as may be; while at the same time the brush clears away as many as possible of the "scales" and their enclosed broods of insects and eggs.

Bearing in mind what has been said just now of the want of certainty in any remedy whatsoever, the tree-grower who follows these directions will most likely find his work successful and his deciduous plants cleaned of "scale" on the bark.

A second method may be adopted—namely, the painting-over of the trunk and branches, without attempting to forcibly detach any "scales" with the brush. This, properly performed and with proper fluids, is likely to be just as efficacious as the other, for the fluid should "run in" under the scales, surround the eggs, and prevent them from hatching. It gives less trouble than the hard brushing, and is equally destructive to the Coccids. It has, however, of course, not the same cleaning effect upon fungoid growths or incrustations impeding the free "respiration" of the plant.

For deciduous trees, then, such as apple- or pear-trees in an orchard, the simple remedy is severe pruning at the dead of winter, and the coating of the trees with a destructive fluid, laid on with a brush on every part, preferably with a hard brush vigorously used, but leaving a thin coat of the fluid on the bark.

It must be thoroughly understood that, a week or two after the first application, the "scales" left on the tree should be examined, and, if the eggs are not killed, a second coating of the fluid should be applied.

The treatment of evergreen plants, or of plants which are attacked both on the bark and leaves, is really the same as the above as regards its object, but it necessarily differs in its method. Here, again, it is desired not only to kill the insects themselves, but also to devitalize the eggs; but in this case the work is much harder, for the eggs are especially difficult to reach. Still, there is this advantage: that in dealing with evergreens the season of the year need not be specially studied, and, in default of touching the eggs, one may get at the young larvæ. The remedy is again a fluid, but it must be applied in the form of spray. Coccids are sometimes found on the upper surfaces of leaves, but as a rule they affect the lower sides. This, of course, renders it much more difficult to get at them; and the ordinary rose of a garden syringe would not, as a general thing, distribute the fluid in a sufficiently-fine form. The finer the spray and the more it is forced into every corner and nook of the plant the better. Various force-pumps and spray-throwers have been invented for this purpose in the United States; but probably tree-growers in this country need only procure the finest possible rose for their syringes, and use them in the ordinary way. The fluid should be thrown as thoroughly as possible on all parts of the plant, every care being taken to direct it most fully against the under sides of the leaves.

The work, then, to be done is in itself simple enough. A destructive fluid must be selected and applied according to the character of the insect and its position on the tree. For covered or naked insects on the bark, apply it with a hard, stiff brush; for covered or naked insects on the leaves, apply it in the form of the finest spray thoroughly forced as much as possible into every nook and cranny, and especially against the under side of the leaves.

The question, "What is the best fluid to use?" is more complicated. Many answers have been given to it: many fluids have been strongly recommended by different people. It must be well remembered that, as stated above, a sure and sovereign remedy has yet to be discovered, and failure may attend even the best suggested at present. Bearing this in mind, tree-growers will find in the following list the result of the experience of a number of observers, which may serve as a useful guide. It does not profess to be more than a summary, compiled from the researches of entomologists such as Mr. Comstock, Professor Riley, Mr. Hubbard; from suggestions by gardeners and others, embodied in various parliamentary and private documents; and from actual observation and experiment in this country: but it is believed that the information here given may be accepted and relied on.

Some of the substances here given are manifestly unsuitable for general use on account of their expense, at any rate in the open air. Yet it is well to include them, as they are all suggested in some work or other, or in the replies of gardeners and fruit-growers to parliamentary inquiries; and the objections to them ought also to be known:—

1. Alcohol. Will certainly kill any individual insect; but "sprayed over scale-insects produced no apparent effect" (Comstock).

2. Ammonia. Whether used pure (diluted) or in urine, damages the plants much more than it does the insects (Hubbard; Comstock).

3. Ashes. Powdered, or mixed with lime, salt, soot, &c. Of no value whatever (Hubbard; Personal experiment).

4. Carbolic acid. Of no avail, either as spray or brushed on, unless used in such strength as to seriously damage the tree (Hubbard; Riley; Comstock).

5. Castor-oil. Has been found efficacious in cleaning hawthorn-trees at the Agricultural College, Lincoln (T. Kirk). It was mixed with soot for some unexplained reason. The time of the year when it was applied is not stated; but the author's experiments seem to show that castor-oil does not effectually kill the eggs. Still, it is doubtless a valuable remedy if applied repeatedly, so as to kill larvæ and adults, supposing it to be sufficiently cheap.

6. Cole's Insect-exterminator. Apparently a mixture of about 2 parts of "green soap" with 100 parts of strong alcohol. It is "effectual as an insecticide, and harmless to growing plants;" but "the cost is too great, except on a small scale, as in conservatories" (Comstock).

7. Gasoline. Seems to have been used in California on pear-trees: result, doubtful (New Zealand Parliamentary Papers: Codlin Moth Committee Report, 1885, page 8).

8. Gishurst compound. Very favourably spoken of in many quarters. In New South Wales it has been found efficacious on orange-trees against Aspidiotus coccineus (Alderton); in Nelson it is said to be used beneficially against Icerya purchasi. It does not, however, kill the eggs with certainty (Personal experiment). Applied warm, and properly diluted, it may be recommended as a good remedy; but applications of it should be repeated.

9. Kerosene. Seemingly the most valuable of all remedies, when properly applied. "Almost the only substance which will certainly kill the eggs without at the same time destroying the plant" (Hubbard).

But the application of this remedy must be carefully performed. Some trees may endure it without injury, even undiluted or unmixed; but this is scarcely to be expected, and the oil should therefore be applied in some mixed form. Also, it is important to remember that a hot sun increases the injurious effect of kerosene; consequently winter, or cloudy weather, should be chosen for its employment.

(a.) Pure kerosene. As just stated, it is probably not advisable to use this. Still, "a young shoot of orange, not more than fourteen days old, was uninjured by an application of pure kerosene which thoroughly wet every leaf;" (Comstock); and Lecanium hesperidum on ivy, similarly treated, was destroyed, without injury to the plant (ibid.).

(b.) Kerosene and milk. An excellent mixture, if milk can be obtained cheap (Riley; Hubbard; Comstock). It must be applied in the form of an "emulsion," sprayed over the tree or brushed on the bark. Hubbard gives the following directions for use: Heat the milk nearly to boiling-point and mix with double the quantity of kerosene; churn violently from ten minutes to half an hour, according to temperature, until a creamy thick fluid is obtained; dilute this with nine or ten times the quantity of water. The mixture is of course purely a mechanical one, as far at least as the water is concerned, and it must be kept constantly stirred, to prevent the substances from separating from the water. For evergreen trees impel the mixture on leaves and branches in the finest possible spray. Sour milk is as useful as fresh.

The object of the milk is not only to lessen the injurious qualities of the kerosene, but also to induce it to mix more freely with the water; but it is the oil alone which destroys the insects and their eggs.

(c.) Kerosene and soap. When milk is not obtainable, or too dear, nothing is so excellent as this mixture. Soap itself (see below) is a useful insecticide, and in combination with kerosene includes the good qualities of both substances. The cheapest possible qualities of soap will do. The mixture, which is, even more than the last, purely mechanical, must be made first of all an "emulsion." The American experiments result in the following recipe and method of using:—

Dissolve the soap in the water heated to boiling, then add the kerosene, and churn the mixture until a creamy fluid results which thickens on cooling. Dilute with nine or ten times the quantity of water: the quantities given above will make about thirty gallons of liquid. Whale-oil soap, soft-soap, or any other kind will do. As with the milk emulsion, apply in the form of the finest spray for evergreens (Riley; Hubbard; Personal experiment).

(d.) Kerosene and oil. Castor-oil, linseed-oil, whale-oil, may be used. A mixture of this kind, in the proportion of 1 part kerosene to 3 or 4 of oil, has been found very efficacious for apple- and other fruit-trees attacked by the common apple-scale (Myt. pomorum). But, as observed above, the mixture must not be laid on too thick. Thinly brushed all over trunk and branches, at dead of winter, it has been found quite successful in destroying both insects and eggs, without injury to the trees (Personal experiment). It would probably not answer for evergreens, on account of expense.

On the whole, it may be said that, as far as certainty can be attained in the matter, there is no substance better for destroying Coccids and their eggs than kerosene in the form of milk or soap emulsion, diluted with water for evergreens or for trees with insects on the leaves as well as on the bark. Probably, for deciduous fruit-trees the kerosene-and-oil mixture is the best.

The great point in favour of this substance is that it destroys the eggs; this, few if any of the others will accomplish.

10. Lime. Of no avail whatever.

11. Lye. Concentrated lye is very frequently recommended. In the New Zealand Parliamentary Papers (Codlin Moth Committee Report, 1885, page 7) several statements will be found apparently most favourable to it; yet in places we find admissions that "it cannot reach all the eggs." In America generally, it has not been found satisfactory: "inferior to kerosene in killing-power, and far more injurious to trees when used in solutions strong enough to be effective as insecticides."

It is quite possible that the action of lye on the fungus accompanying the scale-insects (see Chap. III.) may have led "practical" gardeners to imagine that it cleaned their trees of scale. Comstock says, "I saw most excellent results from the following mixture: 1lb. concentrated lye, one pint gasoline or benzine, half pint oil, five gallons water." Probably the good results here were due, not to the lye, but to the gasoline and oil.

12. Pyrethrum. Useless against Coccids (Comstock).

13. Salt. Useless (Comstock).

14. Soap. Undoubtedly a valuable remedy, and perhaps, in some cases, as efficient as kerosene; but it does not destroy the eggs. A solution of ³/₄lb. of soap to a gallon of water, applied hot, was entirely successful in California: three months after its application no living scale-insect could be found (Comstock). The time of the year is not stated. In another case the solution was applied cold: "four days after no living insect could be found;" but, again, the time of the year is not stated, and no mention is made of the eggs. Still, a strong solution of soap may be said to be one of the best remedies against the larvæ and adult insects—proportions from ¹/₄lb. to ¹/₃lb. soap to one gallon of water (Comstock; Hubbard; Personal experiment).

15. Soda, caustic. Strongly recommended by many persons. It injures the tree, and does not kill the eggs—two things which are decidedly against its use. Gardeners may have been led to employ it from finding that in some instances it clears away the black fungus-growths (Chap. III.), and imagining this to be a clearance also of the scales.

16. Soda, silicate. Kills some insects, but no eggs, and injures the tree (Hubbard).

17. Sulphate of iron. "A common ingredient in patent remedies;" most injurious to vegetation. It does not affect scale-insects (Hubbard).

18. Sulphur. Another substance, the object of a kind of superstitious veneration amongst gardeners. It is excellent against fungoid growth, but of little value against scale-insects. Here, again, the clearing of the black fungus has probably been taken to mean also the destruction of the insects (Hubbard; Comstock; Personal experiment). Comstock says that in America people often bore holes in their trees and stuff them with sulphur, under the notion that the substance will be taken up by the sap, and poison the insects: quite a futile idea.

19. Sulphur and lime. A dangerous compound, and useless unless applied in such strength as to kill the tree. Its fumes are poisonous, and it may seriously injure the face and hands (Hubbard).

20. Sulphur and snuff. Equal parts mixed and dusted over Lecanium hesperidum on a wet day were quite successful (Comstock). But the mixture would be too expensive except for conservatory plants, and doubtless the snuff alone would be quite as efficacious.

21. Sulphuric acid. "Killed nearly all the scale-insects, and very nearly killed the tree" (Hubbard). No mention is made of its action on the eggs.

22. Soot. Useless (Hubbard; Comstock; Personal experiment).

23. Tobacco. A good remedy against larvæ and adults; doubtful against the eggs. Fumigation has no effect on scale-insects, except sometimes on Dactylopidæ, or "mealy bugs" (Hubbard; Comstock; Personal experiment). The tobacco should be applied in a pretty strong solution; but the expense in this country would be probably too great for general use.

24. Whale-oil and whale-oil soap have been already alluded to under the head "Kerosene." They are both useful ingredients in mixture with that substance, if procurable cheaply.

From the foregoing list it will be gathered that, if experiment, combined with knowledge of the habits and life-history of scale-insects, can be relied on, there is no substance better adapted for their destruction than kerosene, mixed with oil, or milk, or soap solution, and carefully applied. It has been already observed that the killing of the eggs is absolutely necessary for thorough clearing-away of the insects; and, to quote again the words of Mr. Hubbard, kerosene is "almost the only substance which will with certainty kill the eggs without at the same time destroying the plant."

But precautions must not be neglected. Persons who recklessly use any remedy, or who apply it too thickly or in too strong proportions, must expect their trees to suffer. Nor must the weather and the time of the year be overlooked. Winter is the best season for all remedies; and, preferably, cool and cloudy days. Again, if substances soluble in water, such as potash or soda lye, soap solutions, &c., be employed, it must be expected that a day's rain will wash a good deal of them off, and greatly reduce their efficacy. These are things which many people forget; they fancy that because somebody has cleared his trees with, say, castor-oil in winter they can do the same thing in full heat of summer; or, because a lye solution has done well in the dry climate of California, that it will be equally good in the rains of New Zealand. Still more is it a fallacy to imagine that rule-of-thumb methods, not founded upon any knowledge of the nature, habits, and life-history of the insects, are likely to be really efficacious.

Little need be said here of a remedy which has had, to some extent, the authority of Professor Riley, and which is recommended by Mr. Howard (Report U.S. Dep. of Agric. 1880-81, p. 351): viz., the transportation or acclimatization of parasites on scale-insects. Doubtless the thing could be done, as experiments in America have shown. But there are plenty of parasitic insects in New Zealand already, and, although they seem to have hitherto confined their work to the native and mostly to the innoxious Coccids, they may at any time begin to attack the others, and it is only a question of time when they will act usefully as efficient checks (see Chap. IV.).

There is one Coccid of which it must be said that, whilst kerosene mixtures will undoubtedly destroy it, by far the best remedy of all is to destroy and burn at once the infested trees. Icerya purchasi is so voracious and universal a feeder, so repulsive in its aspect, and so destructive in its effects that the most drastic remedy is the best. Any one, therefore, having a tree, especially an ornamental or a fruit tree, attacked by Icerya purchasi, is strongly recommended to make no delay, but to cut down and burn every stick of the tree as soon as possible.

It was observed at the beginning of this chapter that some people hold the opinion that the damage done by scale-insects is not of importance. The foregoing remarks upon remedies are not directed to those who hold this view, which is contradicted by the experience not only of other countries but of New Zealand itself.

Authorities referred to in this Chapter.

U.S. Department of Agriculture—

Reports by Professor Riley, Professor Comstock, Mr. Hubbard, Mr. L. O. Howard.

N.Z. Parliamentary Papers, 1885—

Report of the Select Joint Committee of both Houses on the Codlin-moth, and "various blights to which fruits are subject."

Personal experiment by the author and friends.

Replies of farmers, gardeners, and tree-growers to inquiries, official or private.

[CHAPTER VI.]

CATALOGUE OF INSECTS AND DIAGNOSIS OF SPECIES.

Family.—COCCIDIDÆ.

Male and female larvæ similar, apterous, naked or covered, active.

Females in all stages apterous; metamorphosis semi-complete; naked or covered; active or stationary; rostrum usually present in all stages, sometimes absent in adult; feet sometimes absent after larval stage; tarsi where present monomerous; feet, where present, ending in a single claw; eyes sometimes absent.

Male pupæ apterous; naked or covered. Adult males with two wings and two halteres; metamorphosis complete; rostrum present in larva and pupa, always absent in adult; tarsi monomerous; feet ending in a single claw; abdomen terminating in a spike which forms the sheath of the penis; eyes present in adult; ocelli often large, sometimes exceeding three in number.

The above characters sufficiently distinguish this family from the rest of the Homoptera. Probably the first marks for identification of a specimen might be the monomerous tarsus and the single claw. The latter is always to be made out, at least in the earlier stages of the female and in the adult male.

GROUPS.

Larvæ active, naked; adult females and pupæ stationary, covered with separate shields or puparia, composed partly of secretion, partly of the earlier discarded pellicles; females apodous after larval stage; abdomen of females not exhibiting a median cleft or dorsal lobes

[Diaspidinæ.]

Larvæ active, naked; adult females and pupæ active or stationary, naked or covered with secretion; adults sometimes apodous; abdomen of females exhibiting a median cleft and two dorsal lobes

[Lecanidinæ.]

Larvæ active, naked, exhibiting at the abdominal extremity two protruding anal tubercles. Adult females exhibiting abdominal cleft and dorsal lobes; naked or covered with secretion

[Hemicoccidinæ.]

Females in all stages exhibiting anal tubercles; no abdominal cleft or dorsal lobes; naked or covered with secretion

[Coccidinæ.]

Group I.—DIASPIDINÆ.

Female insects covering themselves with separate shields or puparia composed partly of fibrous secretion, partly of the discarded pellicles; females apodous after first stage; no abdominal cleft or lobes; spinnerets usually arranged in groups on the posterior segment of female.

GENERA.

Female puparium circular, pellicles usually in the centre; male puparium slightly elongated, not carinated, pellicle at one end. Four or five groups of spinnerets, or groups absent

[Aspidiotus.]

Female puparium more or less circular, pellicles near the centre; male puparium elongated, carinated, pellicle at one end. Five groups of spinnerets

[Diaspis.]

Female puparium elongated, pellicles at one end; male puparium nearly similar but smaller and narrower, not carinated, pellicle at one end. Five groups of spinnerets

[Mytilaspis.]

Female puparium elongated, pellicles at one end; male puparium much narrower and smaller, carinated, pellicle at one end. Five groups of spinnerets

[Chionaspis.]

Female puparium elongated, pellicles at one end; male puparium narrower, pellicle at one end. More than five groups of spinnerets. Abdomen of female not fringed

[Poliaspis.]

Female puparium elongated, first pellicle at one end, second pellicle almost filling the puparium; male puparium smaller and narrower, sometimes carinated, pellicle at one end

[Fiorinia.]

Genera not yet represented in New Zealand.