Encyclopædia Britannica, Ninth Edition/Turnip-Fly
TURNIP-FLY, Turnip-Flea, or Earth Flea-Beetle, the name applied to several species of Haltica which infest turnip fields and do considerable damage to crops. The genus belongs to the family Chrysomelidx, and includes about 100 species. The turnip-fly most usually met with, Haltica nemoium, is scarcely 2mm. in length and of a shining black colour, with two ochreous yellow longitudinal bands running along each wing-case; the bands are slightly sinuous and bend inwards at the hinder end. Of the eleven-jointed antennas the first three segments are yellow and the remainder black.
Turnip fly (Haltica nemorum).
The coxae are black, the rest of the legs having a yellowish hue. The coxae and tibiae are stout and formed for leaping, especially in the posterior pair of legs. The remarkable power of jumping has given rise to the name turnip-flea. The females are slightly longer and decidedly stouter than the males.
Another species, H. concinna, has a greenish yellow or brassy appearance, and the tibiæ of the two posterior legs are armed with a thorn-like hook. A third species, H. consobrina, is of a dark blue colour above, whilst another species, H. obscurella, often very abundant, is of a lighter blue colour, and larger than those mentioned above.
The life-history of Haltica nemorum may be taken as an example of that of the genus. The beetles begin pairing during April, and continue all through the summer. The female lays but few eggs, usually one a day. The eggs are deposited on the under surface of a leaf, close xinder one of the projecting veins; they possess a protective colouring. The development within the egg lasts ten days, at the end of which a small larva creeps out, and at once eats its way through the lower epidermis of the leaf into the mesophyll and there forms long winding burrows. The larva or maggot is of a yellowish colour and somewhat cylindrical in form. It has three pairs of legs anteriorly and a pair of pro-legs at its hinder end. The most anterior and the most posterior segment bear a black spot. The mouth is provided with a pair of mandibles, by means of which the larva eats its way through the soft tissue of the leaf. This larval condition lasts about six days; the maggot then leaves the leaf and buries itself some one or two inches beneath the surface of the earth; here it turns into a chrysalis. From this the full-grown beetle emerges after an interval of fourteen days, and it is in this stage of its life-history that it proves most destructive to the turnip crop. Several broods may be produced each season; the beetle lives through the winter sheltered under fallen leaves, pieces of wood, clods of earth, &c., until the warmth of spring awakens it, when it soon begins to lay eggs.
Since the chief damage to the crop is due to the perfect beetle devouring the young leaves of the turnip plant, one of the most important methods of dealing with the pest is to ensure a strong and healthy growth of the plant, by means of manuring, watering, &c. Another preventative is the removal of such weeds as the shepherd's purse and charlock, which harbour the insect in great numbers, and the removal of any stubble in which it might pass the winter. When a crop is badly attacked dressings of soot and gas -lime mixed with sulphur and lime, or of soot or lime alone, prove efficacious, but these must be applied whilst the dew is on the leaves or the "fly" will escape.