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Potato Beetle

(Doryphora decemlineata). This insect, also often called the Colorado Beetle, though not yet a resident in the British Islands, is among the best known of insects, by name, at least, to most persons in the United Kingdom, thanks to the scare that arose with regard to it a few years ago. It was first observed in the Rocky Mountains of America, in the Colorado region, feeding on a wild species of Solanum, the genus to which the Potato belongs. When Potatoes were planted by settlers in the beetle's native home, it attacked the new food-plant, throve on it only too well, and commenced to spread rapidly eastward; and in 1876 it reached the Atlantic coast. It is now common along the Eastern States, and in Canada, and it is not impossible that it will be conveyed to, and may be able to establish itself in, our own islands. It has proved able to withstand heat and cold, dry and moist climates; and would probably find our climate suit it. In its passage eastward in America, it committed great havoc in the Potato-fields, and excited fears in the minds of many, lest it should continue, year by year, to inflict severe injury to the Potato crop, and lest it might effect a footing in Britain, as appeared very probable. To guard against this latter risk, the Privy Council of Great Britain and Ireland passed an Order, which was published in the "London Gazette" of August 17th, 1877, to the effect that "If the owner of, or any person having the charge of, any crop of Potatoes, or any vegetable, or substance, finds, or knows to be found, thereon the Colorado Beetle, in any stage of existence, he shall, with all practicable speed, give notice of the same to a Constable of the Police establishment of the locality; . . . . . and it is further provided that it shall not be lawful for any person to sell, keep, or distribute living specimens of the Colorado Beetle in any stage; and any person failing to do anything he is by this Order required to do, is, for each offence, liable to a penalty not exceeding ten pounds." An idea of the general form, size, are markings of the beetle may be obtained from Figs. 261 and 262, and of the larva from Fig. 263. The colours of the beetle are as follows: It is usually straw-yellow above, though, at times, the head and thorax are tawny-yellow, with black spots on them, as shown. The wing-cases each bear five equidistant, black bands, the second and third of which, counting from the middle, frequently meet behind. The legs are tawny-yellow, with black knees and tarsi, and (in, at least, the last pair) black thighs; the antennae are yellow in their basal part, black in the rest of their length. The larva is pale yellow, or, rather, dusky-yellow, or freckled with minute black dots on the back; and there are two rows of larger black dots along each side; the legs are black. The females place their eggs in small clusters on the lower surface of the Potato leaves The eggs are oval, smooth, bright yellow, and glossy. In five or six days, the larvae appear, and in from two to three weeks they are full-fed, and creep under ground, to become pupae. In about a fortnight, the beetles emerge, and the females proceed to egg-laying. In America, three broods are produced each year, the third brood hybernating under ground, or in any suitable retreat. Both larvae and beetles feed on the leaves of Potatoes, and soon leave nothing but the mere ribs, utterly destroying the crop.

In June, 1877, the insect was found at Muhlheim, on the Rhine, and in three places at Schildau, in Prussian Saxony; but it was stamped out by the energetic action of the Prussian Government. Occasional living examples have been found in British seaports, but they have never appeared in this country on the Potato crops. In America, and in Germany, it has been observed that, when they have exhausted the Potato-plants, they resort to low weeds, e.g., Goosefoot, Knotgrass, Hedge Mustard, and even to Cabbage. Remedies. In America, the use of Paris Green, or Scheele's Green (hydrocupric arsenite), sold at about 6d. per lb., is found effectual in saving the crop of Potatoes. It may be dusted on the plants, but it is better to mix it with water, in the strength of a tablespoonful to a bucket of water, and to sprinkle them with this. Caution must be used in handling this substance, as it is a dangerous poison. Hand-picking would probably be sufficient to get rid of the insects on their first appearance in a new locality, at a distance from other habitats, as must be the case in their appearance anywhere in Europe.

For other Beetles destructive to Potatoes, see remarks on INSECTS under Potato.