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ON INSECTS MOST INJURIOUS TO VEGETABLES AND ANIMALS, AND OF THE MEANS BEST CALCULATED TO COUNTERACT THEIR RAVAGES.

NO. II.

By JAMES DUNCAN, M. W. S., &c.

THE Cataphagus obscurus, which we succeeded in rearing last summer from a wire-worm precisely similar to that described towards the close of last paper, and which was mentioned as by far the most destructive species in this country, when in the perfect state has the body short, thick, and convex above, of an obscure dusky or brownish-black colour, clothed throughout with short greyish hairs; the wing-cases usually of a lighter hue than the rest, having the punctured lines placed at equal distances, and the intermediate spaces of a uniform colour. The latter circumstance distinguishes it best from C. lineatus, of which, however, it is likely to be a mere variety, as it corresponds to that insect in almost every other particular. When an attempt is made to seize these insects, they almost invariably contract their legs and antennæ, by which they are liable to slip through the fingers to the ground, where they lie for a time quite motionless; but if they happen to fall on their backs, they speedily jerk themselves into the air with a sharp snap, like a pellet sent from a pop-gun.

The larvæ of these beetles, which alone are noxious, have been ascertained to continue in that state four or five years before undergoing their metamorphosis; and during the whole of that period they live on the roots of corn and other grasses, and likewise attack the bulbs of turnips, carrots, potatoes, &c. The extent of the injury they sometimes occasion may be estimated from the fact, that a single worm has been observed to bite from eight to twenty plants in a very short time, and they are occasionally so abundant, that from four to eight have been turned up by the spade in a space of four square feet. They are by far most destructive in newly broken up grounds, gardens converted from pasture-lands, &c. Mr Spence relates that they prevailed for a time to a great extent in the Botanic Garden at Hull, and completely destroyed the annuals. The following calculation, whatever opinion may be entertained of

the data on which it is founded, will serve to shew the serious damage which these insects have been supposed to commit throughout the kingdom, by an eminent agriculturist who had frequent occasion to investigate the subject.

"The depredations of the wire-worm being principally confined to wheat sown upon clover leys, old pastures recently broken up, pea and bean stubbles, &c., we may suppose the general average of the injury to amount to about a twentieth part of what is sown upon this description of lands. This, I think, may be deemed a very fair and moderate calculation. The number of cultivated acres of land in England at the time in question was computed at seven millions, of which 2,400,000 were calculated to be sown with wheat, and as only one-half of the wheat sown is supposed to be on clover leys, old pastures, &c., our calculations must be confined to 1,200,000 acres, instead of 2,400,000: this will give 60,000 acres as annually destroyed by the insect in question; which replanted, at one bushel per acre, will require 60,000 bushels of seed, which, at 6s. per bushel, are worth L.24,000. Besides this, although no extra expense is incurred by the farmer in preparing the land, yet he has to pay for dibbling-in the seed, which, at 5s. 3d. per acre, will cost L.15,750, or at the full price, 6s. per acre, L.18,000. If the land require harrowing, there will be a further charge of 9d. per acre, or L.2,250, not to name other items, which render it difficult precisely to ascertain the loss of the farmer.

"If the above calculation be thought a fair one, and I see no reason why it should not, we find the quantity of wheat lessened to the market by the depredations of these insects is very frequently, if not annually, sixty thousand bushels, which occasions to the farmers an additional expense of at least L. 15,750." *

When the fields lie fallow, these insects continue to feed on the grass and other weeds, which are frequently allowed to overrun the surface; whereas if the soil were kept clean, they would either die for want of food, or be compelled to remove to some other place.

It has been already stated that these larvæ invariably live beneath the surface of the soil; every plan, therefore, suggested for their destruction, must be founded on this consideration. Without adverting to this fact, many superficial applications, such as strewing the surface with quicklime, soot, &c. have been tried without effect. The most obvious remedy is to saturate the soil with some fluid which has been previously ascer

Linnean Trans. vol. ix. p. 158.—This calculation will not appear too high, at least for certain years, when it is recollected that the hop-fly (Aphis Humuli) sometimes occasions an annual loss of L.453,000 to the British revenue, and that the damage committed in a single county, Devonshire, by the turnipbeetle (Haltica nemorum), has been estimated by an eminent agriculturist at L.100,000 in one year.

tained to destroy the insects without injuring the plants, that is, if the latter be of a kind which it is necessary to preserve, as will usually be the case. In a fallow field this precaution need not be observed, as a double benefit would ensue from the destruction of both insects and weeds. More carefully conducted experiments, and on a more extensive scale than any that have yet been undertaken, will be necessary to shew what kind of liquid is best adapted for this purpose. Probably different substances will be found most useful in different situations, according to the nature of the soil and the chemical ingredients which enter into its composition. The latter consideration should be particularly attended to in all experiments on the subject, as most likely to suggest the most appropriate remedy; and it might even happen that the fluid employed to destroy the insects might be so managed as to produce a most beneficial change in the chemical qualities of the soil. If a strong saline solution, for example, should be found to kill the insects, as it is very likely to do, there are few soils which would not derive benefit from such an application. Of course many substances prove speedily fatal to these insects, and among these the choice would have to be determined by cheapness and ease of application. Beirkander, a Swedish observer, who has investigated their habits, found that they lived among

He suggests, that such of these plants as proved most speedily fatal should be mixed with the manure. He also considers it of great advantage to cause children to follow the plough, and pick up all that happen to be turned up. He states, that in this he has seen 351 wire-worms collected in a field not exceedway ing 600 feet by 56.

Sir Joseph Banks suggested a very simple plan for alluring the wire-worms from the plants, and collecting them that they might be destroyed. This consisted merely in burying slices of potato stuck upon skewers, near the seeds sown. As the larvæ

are very fond of this root, they leave the young plants, and fix upon it. These slices require to be examined every day, and the wire-worms collected upon them destroyed.

A contributor to the British Farmer's Magazine affirms, that he has frequently freed fields entirely from wire-worms, by sowing a crop of white mustard seed. The experiment he has tried so frequently, and in circumstances so well calculated to demonstrate its effects, that he is perfectly satisfied that the remedy is efficient. "Encouraged by the results of my former trials, I sowed a whole field of forty-two acres, which had never repaid me for nineteen years, in consequence of nearly every crop being destroyed by the wire-worm; and I am warranted in stating, that not a single wire-worm could be found the following year; and the crop of wheat throughout, which was reaped last harvest, was superior to any I had grown for twentyone years. I am therefore under a strong persuasion, that the wire-worm may be successfully repelled and eradicated, by carefully destroying all weeds and roots, and drilling white mustard seed, and keeping the ground clean by hoeing."*

Nature herself has taken means to check their superabundant increase by making them the prey of a small ichneumon, which searches out their retreats, and deposits its eggs in their bodies, which are consumed by the parasitical larvæ as soon as hatched.

FLEA-BEETLES (Haltica).

Under this name is included a numerous tribe of small insects, scarcely any of them exceeding two lines in length, and the greater number not above half these dimensions, all of which are herbivorous, and many of them attacking our most useful vegetables. They are at once distinguished from all other beetles occurring in this country (except a few of the weevil tribe, which are always sufficiently recognisable by their elongated rostrum), by having the power of leaping to a considerable distance by means of their hinder legs, the thighs of which are much thickened for the purpose. The external crust, or covering, is in most cases hard and polished, minutely punctured, either in lines, or irregularly; and not a few of them are adorned with very brilliant colours. By far the greater proportion of • Mr Tallant in Brit. Farmer's Mag. 1831.

them are attached to cruciferous or tetradynamous plants, some feeding on several different kinds, and others confining themselves to a single species. They were all comprehended by Linnæus in his genus Altica; but the more careful examination to which they have been subjected since his time, as well as the many additional species discovered, has rendered it necessary to divide them into several generic groups. As every one who attends to the insects injurious to vegetation will have occasion to observe the depredations of several different kinds belonging to this family, it has been thought that it would be useful to subjoin the following synoptical view of the genera, translated from Stephens' Illustrations of Entomology, by which it will be easy to refer the respective species to their proper place in modern systems:

Hinder tibiæ not dentate or spinous externally.

Hinder tarsi short, inserted at the apex of the tibiæ.

Body oblong-ovate.

Thorax narrower than the wing-cases...............................HALTICA.
of the same breadth as the wing-cases... MANTURA,

unequal............................
-------- MNIOPHILA.

Hinder tarsi elongate, inserted at the apex of the tibiæ..THYAMIS.
remote from the apex of the tibia....MACROCNEMA.

Hinder tibiæ dentate or spinous externally.

the head prominent..........................

spinous, head drawn within the thorax..

...CHATOCNEMA.

Species belonging to several of these genera are very hurtful to the produce of our fields and gardens; but the most troublesome are those composing the group to which the old name Haltica is still applied. One of them, H. oleracea, attacks cabbage, broccoli, &c., and often seriously injures the young plants, by consuming the leaves. But by far the most formidable enemy to the farmer and horticulturist is that species named H. nemorum, which feeds on the turnip. As one of the most constant and active depredators to which that invaluable plant is exposed, it is highly desirable that its history should be thoroughly investigated, with a view to the discovery of some efficient remedy; and we shall therefore proceed to mention the principal particulars which we have been able to ascertain in regard to it.