Our national beverage ale, so valuable and heartening to the lower orders, and so infinitely preferable to ardent spirits and tea, is indebted to another vegetable, the hop, for its agreeable conservative bitter. This plant so precious has numberless enemies in the Lilliputian world to which I am introducing you. Its roots are subject to the attack of the caterpillar of a singular species of moth (Hepiolus Humuli), known to collectors by the name of the ghost, that sometimes does them considerable injury[301].—A small beetle also (Haltica concinna) is particularly destructive to the tender shoots early in the year; and upon the presence or absence of Aphides, known by the name of the fly, as in the case of peas, the crop of every year depends; so that the hop-grower is wholly at the mercy of insects. They are the barometer that indicates the rise and fall of his wealth.
If the beer-drinker be thus interested in the history of these animals, equally so is the drinker of tea. Indeed sugar is an article so universally useful and agreeable, that what concerns the cane that produces it seems to concern every one. This also affords a tempting food to insects. The caterpillar of a white moth, called the borer, for destroying which a reward of fifty guineas is offered by the Society of Arts, is in this respect a great nuisance, as is an unknown species of horned beetle[302]. An ant also (Formica analis) makes a lodgement in the interior of the sugar-cane in Guinea, and destroys it.—But the creature of this class most destructive to the sugar-cane, is one of the latter genus that does not devour it, and is therefore improperly called Formica saccharivora by Linné; but, by making its nest for shelter under the roots, so injures the plants that they become unhealthy and unproductive. These insects about seventy years ago appeared in such infinite hosts in the island of Granada, as to put a stop to the cultivation of this plant; and a reward of 20,000l. was offered to any one who should discover an effectual mode of destroying them. Their numbers were incredible. They descended from the hills like torrents, and the plantations, as well as every path and road for miles, were filled with them. Many domestic quadrupeds perished in consequence of this plague. Rats, mice, and reptiles of every kind became an easy prey to them; and even the birds, which they attacked whenever they alighted on the ground in search of food, were so harassed as to be at length unable to resist them. Streams of water opposed only a temporary obstacle to their progress, the foremost rushing blindly on to certain death, and fresh armies instantly following, till a bank was formed of the carcases of those that were drowned sufficient to dam up the waters, and allow the main body to pass over in safety below. Even the all-devouring element of fire was tried in vain. When lighted to arrest their route, they rushed into the blaze in such myriads of millions as to extinguish it. Those that thus patriotically devoted themselves to certain death for the common good, were but as the pioneers or advanced guard of a countless army, which by their self-sacrifice was enabled to pass unimpeded and unhurt. The intire crops of standing canes were burnt down, and the earth dug up in every part of the plantations. But vain was every attempt of man to effect their destruction, till in 1780 it pleased Providence at length to annihilate them by the torrents of rain which accompanied a hurricane most fatal to the other West India Islands. This dreadful pest was thought to have been imported[303]. Besides these enemies, the sugar-cane has also its Aphis, which sometimes destroys the whole crop[304]; and according to Humboldt and Bonpland the larva of Elater noctilucus feeds in it[305].
Two other vegetable productions of the New World, cotton and tobacco, which are also valuable articles of commerce, receive great injury from the depredations of insects. M'Kinnen, in his Tour through the West Indies, states that in 1788 and 1794 two-thirds of the crop of cotton in Crooked Island, one of the Bahamas, was destroyed by the chenille (probably a lepidopterous larva); and the red bug, an insect equally noxious, stained it so much in some places as to render it of little or no value. Browne relates that in Jamaica a bug destroys whole fields of this plant, and the caterpillar of that beautiful butterfly Helicopis Cupido also feeds upon it[306]. That of a hawk-moth, Sphinx Carolina, is the great pest of Tobacco; and it is attacked likewise by the larva of a moth, Phalæna Rhexiæ, Smith[307], and by other insects of the names and kind of which I am ignorant.
Roots are another important object of agriculture, which, however, as to many of them, they may seem to be defended by the earth that covers them, do not escape the attack of insect enemies.—The carrot, which forms a valuable part of the crop of the sand-land farms in Suffolk, is often very much injured, as is also the parsnip, by a small centipede (Geophilus electricus), and another polypod (Polydesmus complanatus), which eat into various labyrinths the upper part of their roots; and they are both sometimes totally destroyed by the maggot of some dipterous insect, probably one of the Muscidæ. I had an opportunity of noticing this in the month of July, in the year 1812, in the garden of our valued friend the Rev. Revett Sheppard of Offton in Suffolk. The plants appeared many of them in a dying state; and upon drawing them out of the ground to ascertain the cause, these larvæ were found with their head and half of their body immersed in the root in an oblique direction, and in many instances they had eaten off the end of it.
America has made us no present more extensively beneficial, compared with which the mines of Potosi are worthless, than the potato. This invaluable root, which is now so universally cultivated, is often, in this country, considerably injured by the two insects first mentioned as attacking the carrot. The Death's-head-hawk-moth (Acherontia Atropos) in its larva state feeds upon its leaves, though without much injury. In America it is said to suffer much from two beetles (Cantharis cinerea and vittata), of the same genus with the blister-beetle[308]; and in the island of Barbadoes some hemipterous insect, supposed to be a Tettigonia, occasionally attacks them. In 1734 and 1735 vast swarms of them devoured almost every vegetable production of that island, particularly the potato, and thus occasioned such a failure of this excellent esculent, especially in one parish, that a collection was made throughout the island for the relief of the poor, whose principal food it forms.
The chief dependence of our farmers for the sustenance of their cattle in the winter is another most useful root, the turnip. And they have often to lament the distress occasioned by a failure in this crop, of which these minor animals are the cause. On its first coming up, as soon as the cotyledon leaves are unfolded, a whole host of little jumping beetles, composed chiefly of Haltica Nemorum, called by farmers the fly[309] and black jack, attack and devour them; so that on account of their ravages the land is often obliged to be resown, and frequently with no better success. It has been calculated by an eminent agriculturist, that from this cause alone the loss sustained in the turnip crops in Devonshire in 1786 was not less than 100,000l.[310] Almost as much damage is sometimes occasioned by a little weevil (Ceutorhynchus contractus) which in the same manner pierces a hole in the cuticle. When the plant is more advanced, and out of danger from these pygmy foes, the black larva of a saw-fly takes their place, and occasionally does no little mischief, whole districts being sometimes nearly stripped by them; so that in 1783 many thousand acres were on this account ploughed up[311].—The caterpillar of the cabbage-butterfly (Pontia Brassicæ) is also sometimes found upon the turnip in great numbers; and Sir Joseph Banks informs me that forty or fifty of the insects before mentioned[312], called by Mr. Walford the wire-worm, have been discovered in October just below the leaves in a single bulb of this plant.—The small knob or tubercle often observable on these roots is inhabited by a grub, which, from its resemblance to one found in similar knobs on the roots of Sinapis arvensis, from which I have bred Ceutorhynchus contractus (Curculio Marsh) and C. assimilis, small weevils nearly related to each other[313]. This, however, does not seem to affect their growth. Great mischief is occasionally done to the young plants by the wire-worm. I was shown a field last summer in which they had destroyed one-fourth of the crop, and the gentleman who showed them to me calculated that his loss by them would be 100l. One year he sowed a field thrice with turnips, which were twice wholly, and the third time in great part, cut off by this insect.—Whether the disease to which turnips are subject, in some parts of the kingdom, from the form of the excrescences into which the bulb shoots, called fingers and toes, be occasioned by insects, is not certainly known[314].
We have wandered long enough about the fields to observe the progress of insect devastation; let us now return home to visit the domains of Flora and Pomona, that we may see whether their subjects are exposed to equal maltreatment. If we begin with the kitchen-garden, we shall find that its various productions, ministering so materially to our daily comfort and enjoyment, almost all suffer more or less from the attack of the animals we are considering.—Thus, the earliest of our table dainties, radishes, are devoured by the maggot of a fly (Anthomyia Radicum), and our lettuces by the caterpillars of several species of moth; one of which is the beautiful tiger-moth (Euprepia Caja), another the pot-herb-moth (Mamestra oleracea), a third anonymous, described by Reaumur as beginning at the root, eating itself a mansion in the stem, and so destroying the plant before it cabbages[315]. And when they are come to their perfection and appear fit for the table, their beauty and delicacy are often marred by the troublesome earwig, which, insinuating itself into them, defiles them with its excrements.—What more acceptable vegetable in the spring than broccoli? Yet how dreadfully is its foliage often ravaged in the autumn by numerous hordes of the cabbage-butterfly! so that, in an extensive garden, you will sometimes see nothing left of the leaves except the veins and stalks.—What more useful, again, than the cabbage? Besides the same insect, which injures them in a similar way, in some countries they are infested by the caterpillar of a most destructive moth (Mamestra Brassicæ), to which indeed I have before alluded[316]; which, not content with the leaves, penetrates into the very heart of the plant[317].—One of the most delicate and admired of all table vegetables, concerning which gardeners are most apt to pride themselves, and bestow much pains to produce in perfection, I mean the cauliflower, is often attacked by a fly, which ovipositing in that part of the stalk covered by the earth, the maggots when hatched occasion the plant to wither and die, or to produce a worthless head[318]. Even when the head is good and handsome, if not carefully examined previous to being cooked, it is often rendered disgusting by earwigs that have crept into it, or the green caterpillar of Pontia Rapæ.
Our peas, beans, carrots, parsnips, turnips, and potatos are attacked in the garden by the same enemies that injure them in the fields[319]; I shall therefore dismiss them without further notice, and point out those which infest another of our most esteemed kinds of pulse, kidney beans. These are principally Aphides, which in dry seasons are extremely injurious to them. The fluid which they secrete, falling upon the leaves, causes them to turn black as if sprinkled with soot; and the nutriment being subtracted from the pods by their constant suction, they are prevented from coming to their proper size or perfection. The beans also which they contain are sometimes devoured by the caterpillar of a small moth[320].—Onions, which add a relish to the poor man's crusts and cheese, and form so material an ingredient in the most savory dishes of the rich, are also the favourite food of the maggot of a fly, that often does considerable damage to the crop.—From this maggot (for a supply of onions containing which I have to thank my friend Mr. Campbell, surgeon, of Hedon near Hull, where it is very injurious, particularly in light soils,) I have succeeded in breeding the fly, which proves of that tribe of the Linnean genus Musca, now called Scatophaga. Being apparently undescribed, and new to my valued correspondent Count Hoffmansegg to whom I sent it, I call it S. Ceparum[321].—The diuretic asparagus, towards the close of the season, is sometimes rendered unpalatable by the numerous eggs of the asparagus beetle (Lema Asparagi), and its larvæ feed upon the foliage after the heads branch out.—Cucumbers with us enjoy an immunity from insect assailants; but in America they are deprived of this privilege, an unascertained species, called there the cucumber-fly, doing them great injury[322].—And, to name no more, mushrooms, which are frequently cultivated and much in request, often swarm with the maggots of various Diptera and Coleoptera.