The maggot, or larvæ, here described is that of a fly called the Anthomyia (Pegomyia) betæ, mangel-wurzel fly. An allied species will sometimes be found on the common dock-leaves, mining their galleries between the dermal cells of the leaves.
We have for some time observed the increase of this pest, and we are prepared to state that now we seldom see a crop that is not greatly injured by its attacks. Mr. Curtis thinks that the best method to destroy them is to employ boys to crush the leaves between the thumb and fingers at the part where the larvæ can be seen; and with this we fear we must for the present be content, unless we could devise some means to take the fly before its eggs are laid in the leaves.
We need not here dwell at length upon the natural history of those pests of the turnip—the Haltica nemorum (striped flea-beetle), and H. concinna (black flea-beetle), as the nature of their ravages are tolerably well known. Thus much, however, may be said; namely:—
a. These insects are called fleas because they have the power of hopping on being disturbed, much after the manner of a flea.
b. They have some five or six broods each year; the earlier ones probably being bred on charlocks and other weeds of the same natural order as the turnip; and hence, then, charlocks are pests, not only as being weeds, but as breeding-places for one of our most mischievous insects.
c. They migrate from their weed-haunts to the first crop of turnips, where much of their mischief may be prevented by simply dusting over the young plants with any fine powder, road-dirt answering the purpose as well as anything else.
Various devices have been employed for keeping away and killing these little creatures. We have used a contrivance for catching them, which may be described as follows:—
Some thin board (or boards), making a surface of about 4 feet long by 2 feet wide, is furnished at one end with a pair of light wheels of just sufficient diameter to lift the board about 2 or 3 inches above the plants. To the other end may be attached two crooked handles in such a manner that the machine can be wheeled flatly over the plants, or if four wheels be employed, one at each corner, a single handle can be used either to push or pull the implement. When used, it should have its underside painted over with tar or any handy viscid substance.
This should be used on bright days, the operator pushing it over the rows of turnips, so as, if possible, not to throw his shadow before. The middle of the day will be best, not only for this reason, but also because these creatures feed more actively at that time.
Now, our experience in the use of this simple contrivance on small experimental plots convinces us that a small boy could easily keep under the enemy in a good-sized field.
But now comes a very important question for consideration. Cannot we do more than kill a few of these creatures? cannot we adopt such plans as will render our crops tolerably safe from their depredations? We think so, and to this end advise the following method of proceeding:—
Let each turnip-grower prepare for the enemy by sowing from the eighth to a quarter of an acre of turnips in a sunny part of the farm as early as the first week in April. These patches would quickly attract all the turnip flea-beetles from the wild cruciferæ on which the first broods seem to depend, and in this small compass they can be killed in detail with the simple contrivance just described, so that when the real crop comes up there will be none, or at least only a few, beetles to emigrate to it; whereas, as we now manage, by the time the crop of turnips is sown, enough of the creatures are too often bred to render it necessary to sow two or three times before we can secure a crop.