Prairie Farmer, Vol. 56: No. 3, January 19, 1884 | Page 2

sent this communication to Professor Forbes, State Entomologist and received the following reply:
EDITOR PRAIRIE FARMER--There can be hardly a shadow of a doubt that the injury which your correspondent so graphically describes is due to the corn root-worm (Diabrotica longicornis), a full account of which will be found in my report for 1882, published last November.
The clue to his whole difficulty lies in the sentence, "I plant my corn every year on the same ground." As the beetles from which the root-worms descend lay their eggs in corn fields in autumn, and as these eggs do not hatch until after corn planting in the following spring, a simple change of crops for a single year, inevitably starves the entire generation to death in the ground.
I inclose a slip, giving a brief account of this most grievous pest; but the article in my last report already referred to will be found more satisfactory.
S. A. FORBES. NORMAL, ILL., January 3.
P.S.--You will probably remember that I published a paper on this insect in THE PRAIRIE FARMER for December 30, 1882.
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The following is the description referred to:
From the "Crop Report" for 1882.
"The corn-root worm, in the form in which it affects the roots of corn, is a slender white grub, not thicker than a pin, from one fourth to three-eighths of an inch in length, with a small brown head, and six very short legs. It commences its attack in May or June, usually at some distance from the stalk, towards which it eats its way beneath the epidermis, killing the root as fast as it proceeds. Late in July or early in August it transforms in the ground near the base of the hill, changing into a white pupa, about fifteen-hundredths of an inch long and two-thirds that width, looking somewhat like an adult beetle, but with the wings and wing-covers rudimentary, and with the legs closely drawn up against the body. A few days later it emerges as a perfect insect, about one-fifth of an inch in length, varying in color from pale greenish-brown to bright grass-green, and usually without spots or markings of any kind. The beetle climbs up the stalk, living on fallen pollen and upon the silk at the tip of the ear until the latter dies, when a few of the beetles creep down between the husks, and feed upon the corn itself, while others resort for food to the pollen of such weeds in the field as are at that time in blossom. In September and October the eggs are laid in the ground upon or about the roots of the corn, and most of the beetles soon after disappear from the field. They may ordinarily be found upon the late blooming plants, feeding as usual upon the pollen of the flowers, and also to some extent upon molds and other fungi, and upon decaying vegetation. There can be no further doubt that the insect is single-brooded, that it hibernates in the egg as a rule, and that this does not hatch until after the ground has been plowed and planted to corn in the spring probably in May or June.
"Although the adult beetles, when numerous, do some harm by eating the silk before the kernels are fertilized by the pollen, and also destroy occasionally a few kernels in the tip of the ear, yet the principal injury is done by the larva in its attack upon the roots. The extent of this injury depends not only upon the number of the worms, but also upon the soil and weather and the general condition of the crop, being worst on high land and in dry weather. Under specially unfavorable circumstances the loss due to the insect may amount to from one-fourth to one-half or even three-fourths of the crop; but when the conditions are generally favorable, it rarely amounts to more than ten or twenty per cent, and frequently even to less. Although the roots penetrated by the larv? die and decay, thrifty corn will throw out new ones to replace those lost. The hold of the stalk upon the ground is often so weakened that a slight wind is sufficient to prostrate the corn. Under these circumstances it will often throw out new roots from the joints above the ground, thus rallying to a certain extent against serious injury.
"As the result of numerous observations and comparisons, it is clearly to be seen that little or no mischief is done except in fields that have been in corn during the year or two preceding, and a frequent change of crops is therefore a complete preventive. Beyond this, the life history of the insect gives us little hope of fighting it effectually except at too great expense, as the eggs and worms are scattered