The insects just enumerated are partial in their attacks, confining themselves to one or two kinds of our pulse or other vegetables. But there are others that devour more indiscriminately the produce of our gardens; and of these in certain seasons and countries we have no greater and more universal enemy than the caterpillar of a moth called by entomologists Plusia Gamma, from its having a character inscribed in gold on its primary wings, which resembles that Greek letter. This creature affords a pregnant instance of the power of Providence to let loose an animal to the work of destruction and punishment. Though common with us, it is seldom the cause of more than trivial injury; but in the year 1735 it was so incredibly multiplied in France as to infest the whole country. On the great roads, whereever you cast your eyes, you might see vast numbers traversing them in all directions to pass from field to field; but their ravages were particularly felt in the kitchen-gardens, where they devoured every thing, whether pulse or pot-herbs, so that nothing was left besides the stalks and veins of the leaves. The credulous multitude thought they were poisonous, report affirming that in some instances the eating of them had been followed by fatal effects. In consequence of this alarming idea, herbs were banished for several weeks from the soups of Paris. Fortunately these destroyers did not meddle with the corn, or famine would have followed in their train. Reaumur has proved that a single pair of these insects might in one season produce 80,000; so that, were the friendly Ichneumons removed, to which the mercy of Heaven has given it in charge to keep their numbers within due limits, we should no longer enjoy the comfort of vegetables with our animal food, and probably soon become the prey of scorbutic diseases[323].—I must not overlook that singular animal the mole-cricket, (Gryllotalpa vulgaris,) which is a terrible devastator of the produce of the kitchen-garden. It burrows under ground, and devouring the roots of plants thus occasions them to wither, and even gets into hot-beds. It does so much mischief in Germany, that the author of an old book of gardening, after giving a figure of it, exclaims, "Happy are the places where this pest is unknown!"
The flowers and shrubs, that form the ornament of our parterres and pleasure-grounds, seem less exposed to insect depredation than the produce of the kitchen-garden; yet still there are not a few that suffer from it. The foliage of one of our greatest favourites, the rose, often loses all its loveliness and lustre from the excrements of the Aphides that prey upon it. The leaf-cutter bee also (Megachile[324] centuncularis), by cutting pieces out to form for its young its cells of curious construction, disfigures it considerably; and the froth frog-hopper (Cercopis spumaria) aided by the saw-fly of the rose (Hylotoma Rosæ) contributes to check the luxuriance of its growth, and to diminish the splendour of its beauty.—Reaumur has given the history of a fly (Merodon Narcissi) whose larva feeds in safety within the bulbs of the Narcissus, and destroys them; and also of another, though he neglects to describe the species, which tarnishes the gay parterre of the florist, whose delight is to observe the freaks of nature exhibited in the various many-coloured streaks which diversify the blossom of the tulip, by devouring its bulbs[325].—Ray notices another mentioned by Swammerdam, probably Bibio hortulana, which he calls the deadliest enemy of the flowers of the spring. He accuses it of despoiling the gardens and fields of every blossom, and so extinguishing the hope of the year[326]. But you must not take up a prejudice against an innocent creature, even under the warrant of such weighty authority; for the insect which our great naturalist has arraigned as the author of such devastation is scarcely guilty, if it be at all a culprit, in the degree here alleged against it. As it is very numerous early in the year, it may perhaps discolour the vernal blossoms, but its mouth is furnished with no instrument to enable it to devour them.
In our stoves and greenhouses the Aphides often reign triumphant; for, if they be not discovered and destroyed when their numbers are small, their increase becomes so rapid and their attack so indiscriminate, that every plant is covered and contaminated by them, beauty being converted into deformity, and objects before the most attractive now exciting only nausea and disgust. The Coccus (C. Hesperidum) also, which looks like an inanimate scale upon the bark, does considerable injury to the two prime ornaments of our conservatories, the orange and the myrtle; drawing off the sap by its pectoral rostrum, and thus depriving the plant of a portion of its nutriment, at the same time that it causes unpleasant sensations in the beholder from its resemblance to the pustule of some cutaneous disease.
I must next conduct you from the garden into the orchard and fruitery; and here you will find the same enemies still more busy and successful in their attempts to do us hurt.—The strawberry, which is the earliest and at the same time most grateful of our fruits, enjoys also the privilege of being almost exempt from insect injury. A jumping weevil (Orchestes Fragariæ) is said by Fabricius to inhabit this plant; but as the same species is abundant in this country upon the beech, the beauty of which it materially injures by the numberless holes which it pierces in the leaves, and has I believe never been taken upon the strawberry, it seems probable that Smidt's specimens might have fallen upon the latter from that tree[327]. The only insect I have observed feeding upon this fruit is the ant, and the injury that it does is not material.—The raspberry, the fruit of which arrives later at maturity, has more than one species of these animals for its foes. Its foliage sometimes suffers much from the attack of Melolontha horticola[328], a little beetle related to the cockchafer: when in flower the footstalks of the blossom are occasionally eaten through by a more minute animal of the same order, Byturus tomentosus, which I once saw prove fatal to a whole crop; and bees frequently anticipate us, and by sucking the fruit with their proboscis spoil it for the table.—Gooseberries and currants, those agreeable and useful fruits, a common object of cultivation both to poor and rich, have their share of enemies in this class. The all-attacking Aphides do not pass over them, and the former especially are sometimes greatly injured by them; their excrement falling upon the berries renders them clammy and disgusting, and they soon turn quite black from it. In July 1812 I saw a currant-bush miserably ravaged by a species of Coccus, very much resembling the Coccus of the vine. The eggs were of a beautiful pink, and enveloped in a large mass of cotton-like web, which could be drawn out to a considerable length. Sir Joseph Banks lately showed me a branch of the same shrub perforated down to the pith by the caterpillar of Æegeria tipuliformis: the diminished size of the fruit points out, he observes, where this enemy has been at work. In Germany, where perhaps this insect is more numerous, it is said to destroy not seldom the larger bushes of the red currant[329]. The foliage of these fruits often suffers much from the black and white caterpillar of Abraxas grossulariata; (this was the case last spring at Hull;) but their worst and most destructive enemy, particularly of the gooseberry, is that of a small saw-fly. This larva is of a green colour, shagreened as it were with minute black tubercles, which it loses at its last moult. The fly attaches its eggs in rows to the underside of the leaves. When first hatched, the little animals feed in society; but having consumed the leaf on which they were born, they separate from each other, and the work of devastation proceeds with such rapidity, that frequently, where many families are produced on the same bush, nothing of the leaves is left but the veins, and all the fruit for that year is spoiled[330].
Upon the leaves of the cherry, which usually succeeds the gooseberry, in common with those of the pear and several other fruit-trees, the slimy larva of another saw-fly (Tenthredo Cerasi) makes its repast, yet without being the cause of any very material injury. But in North America a second species nearly related to it, known there by the name of the slug-worm, has become prevalent to such a degree as to threaten the destruction not only of the cherry, but also of the pear, quince, and plum. In 1797 they were so numerous that the smaller trees were covered by them; and a breeze of air passing through those on which they abounded became charged with a very disagreeable and sickening odour. Twenty or thirty were to be seen on a single leaf; and many trees, being quite stripped, were obliged to put forth fresh foliage, thus anticipating the supply of the succeeding year and cutting off the prospect of fruit[331].—In some parts of Germany the cherry-tree has an enemy equally injurious. A splendid beetle of the weevil tribe (Rynchites Bacchus) bores with its rostrum through the half-grown fruit into the soft stone, and there deposits an egg. The grub produced from it feeds upon the kernel, and, when about to become a pupa, gnaws its way through the cherry, and sometimes not one in a thousand escapes[332]. This insect is fortunately rare with us, and has usually been found upon the black-thorn. The cherry-fly also (Tephritis Cerasi) provides a habitation for its maggot in the same fruit, which it invariably spoils[333].
The different varieties of the plum are every year more or less injured by Aphides; and a Coccus (C. Persicæ?) sometimes so abounds upon them that every twig is thickly beaded with the red semiglobose bodies of the gravid females, whose progeny in spring exhaust the trees by pumping out the sap.
The blossoms of our pear-trees, as we learn from Mr. Knight, are often rendered abortive by the grub of a brown beetle: and a considerable quantity of its fruit is destroyed by that of a small four-winged fly, which occasions it to drop off prematurely[334]. This would seem to be a saw-fly, and is probably the species which Reaumur saw enter the blossom of a pear before it was quite open, doubtless to deposit its eggs in the embryo fruit. He often found in young pears, on opening them, a larva of this genus[335].—A little moth likewise is mentioned by Mr. Forsyth as very injurious to this tree[336].
But of all our fruits none is so useful and important as the apple, and none suffers more from insects, which according to Mr. Knight[337] are a more frequent cause of the crops failing than frost. The figure-of-eight moth (Episema cæruleocephala), Linné denominates the pest of Pomona and the destroyer of the blossoms of the apple, pear, and cherry.—He also mentions another (Tinea Corticella) as inhabiting apple-bearing trees under the bark.—And Reaumur has given us the history of a species common in this country, and producing the same effect, often to the destruction of the crop, the caterpillar of which feeds in the centre of our apples, thus occasioning them to fall[338]. Even the young grafts, I am informed by an intelligent friend[339], are frequently destroyed, sometimes many hundreds in one night, in the nurseries about London, by Curculio Vastator, Marsh., (Otiorhynchus? picipes) one of the short-snouted weevils; and the foundation of canker in full-grown trees is often laid by the larvæ of Semasia Wœberana[340]. The sap too is often injuriously drawn off by a minute Coccus, of which the female has the exact shape of a muscle-shell (C. arborum linearis, Geoffr.), and which Reaumur has accurately described and figured[341]. This species so abounded in 1816 on an apple-tree in my garden, that the whole bark was covered with it in every part; and I have since been informed by Joshua Haworth, jun. Esq. of Hull, that it equally infests other trees in the neighbourhood. Even the fruit of a golden pippin which he sent me were thickly beset with it.—But the greatest enemy of this tree, and which has been known in this country only since the year 1787, is the apple-aphis, called by some the Coccus, and by others the American blight. This is a minute insect, covered with a long cotton-like wool transpiring from the pores of its body, which takes its station in the chinks and rugosities of the bark, where it increases abundantly, and by constantly drawing off the sap causes ultimately the destruction of the tree. Whence this pest was first introduced is not certainly known. Sir Joseph Banks traced its origin to a nursery in Sloane Street; and at first he was led to conclude that it had been imported with some apple-trees from France. On writing, however, to gardeners in that country, he found it to be wholly unknown there. It was therefore, if not a native insect, most probably derived from North America, from whence apple-trees had also been imported by the proprietor of that nursery. Whatever its origin, it spread rapidly. At first it was confined to the vicinity of the metropolis, where it destroyed thousands of trees. But it has now found its way into other parts of the kingdom, particularly into the cyder counties; and in 1810 so many perished from it in Gloucestershire, that, if some mode of destroying it were not discovered, it was feared the making of cyder must be abandoned. This valuable discovery, it is said, has since been made; the application of the spirit of tar to the bark being recommended as effectual[342]. Sir Joseph Banks long ago extirpated it from his own apple-trees, by the simple method of taking off all the rugged and dead old bark, and then scrubbing the trunk and branches with a hard brush[343].
Our more dainty and delicate fruits, at least such as are usually so accounted, the apricot, the peach, and the nectarine, originally of Asiatic origin, are not less subject to the empire of insects than the homelier natives of Europe. Certain Aphides form a convenient and sheltered habitation for themselves, by causing portions of the leaves to rise into hollow red convexities; in these they reside, and, with their rostrum pumping out the sap, in time occasion them to curl up, and thus deform the tree and injure the produce. The fruit is attacked by various other enemies of this class, against which we find it not easy to secure it: wasps, earwigs, flies, wood-lice, and ants, which last communicate to it a disagreeable flavour, all share with us these ambrosial treasures; the first of them as it were opening the door, by making an incision in the rind, and letting in all the rest.—The nucleus of the apricot is also sometimes inhabited by the caterpillar of a moth, which devouring the kernel causes the fruit to fall prematurely[344].—In this country, however, these fruits may be regarded as mere luxuries, and therefore are of less consequence; but in North America they constitute an important part of the general produce, at least the peach, serving both as food for swine, and furnishing by distillation a useful spirit. The ravages committed upon them there by insects are so serious, that premiums have been offered for extirpating them. A species of weevil, perhaps a Rynchites, enters the fruit when unripe, probably laying its eggs within the stone, and so destroys them. And two kinds of Zygæna, by attacking the roots do a still greater injury to the trees[345].—A Coccus, as it should seem from the description, imported about thirty years ago from the Mauritius, or else with the Constantia vine from the Cape of Good Hope, has destroyed nearly nine-tenths of the peach-trees in the Island of St. Helena, where formerly they were so abundant, that, as in North America, the swine were fed with them. Various means have been employed to destroy this plague, but hitherto without success[346].—The imperial pine-apple, the glory of our stoves, and the most esteemed of the gifts of Pomona, cannot, however precious, be defended from the injuries of a singular species of mite, the red Spider[347] of gardeners, (Erythræus telarius) which covers them, and other stove plants, with a most delicate but at the same time very pernicious web.—The olive-tree, so valuable to the inhabitants of the warmer regions of Europe, often nourishes in its berries the destructive maggot of a fly (Oscinis Oleæ); and the caterpillar of a little moth (Tinea Oleella), which preys upon the kernel of the nucleus, occasions them to fall before they are ripe.—Every one who eats nuts knows that they are very often inhabited by a small white grub; this is the offspring of a weevil (Balaninus Nucum) remarkable for its long and slender rostrum, with which it perforates the shell when young and soft, and deposits an egg in the orifice.—In France it sometimes happens, when the chestnuts promise an abundant crop, that the fruit falls before it comes to maturity, scarcely any remaining upon the trees. The caterpillar of a moth which eats into its interior is the cause of this disappointment[348].—Of fruits the date has the hardest nucleus; yet an insect of the same tribe with the above, that feeds upon its kernel, is armed with jaws sufficiently strong to perforate it, that it may make its escape when the time of its change is arrived, and assume the pupa between the stone and the flesh. The date is eaten also by a beetle which Hasselquist calls a Dermestes[349].