Twenty-nine species of insects indigenous to the infested area parasitize the borer. None has been numerous enough to have a great effect on the borers. Scientists have tried to supplement the natural occurrence of Trichogramma minutum, a parasite that occasionally destroys a high percentage of the later portion of the second-generation eggs, by rearing a stock supply of parasites in the laboratory and releasing them when first- or second-generation eggs were present. Neither permanent nor appreciable temporary benefit resulted from the efforts.

Predators exert some influence on the borers.

Birds, particularly the downy woodpecker (Dryobates pubescens inedianus) and the red-winged blackbird (Agelaius phoeniceus phoeniceus), and insect predators, particularly the lady beetles Ceratomegilla fuscilabris and Hippodamia convergens, have been frequently observed removing large numbers of borer larvae and egg masses from corn plants. No predators have been imported for testing against the corn borer.

The only disease organism that has been observed to kill the corn borer in the field in the United States is Beauveria bassiana and then only under circumstances directly traceable to infection originating in the laboratory. B. bassiana is an insectivorous organism that probably was brought into the United States on imported larvae. Field recoveries of this disease have been made immediately following its dissemination, but evidently no lasting effect has resulted from efforts to establish it as a natural control.

THE DISPOSAL of host plants in such a way as to destroy the borers infesting them is a logical and effective way to combat the borer. We have conducted a great deal of research to determine the best ways to do that. By the use of traps, for catching surviving borers, consisting of a rectangle of boards set on edge in the test ground and lined on the inside with strips of corrugated paper, the most efficient equipment was developed and information on the number of borers killed as a result of being buried at various depths in many types of soil was obtained. Because of the ability of the borer to reproduce at a very high rate and because of the mortality caused by many natural factors it is doubtful if disposal of host plants will prove highly beneficial unless a thorough community-wide effort is made. Because most of the mechanical methods of control are actually good farm practices, however, it is wise to follow them.

Feeding infested plants to livestock is one way to fight the corn borer. Their food value is not noticeably reduced unless they are severely infested. Infested corn plants can be fed as silage, direct from the field, or as finely shredded or cut fodder. Properly done, any of these methods destroys nearly all the borers in the plants.

Any infested corn that is put in the silo should be cut close to the ground. Borers that escape the silage cutter are destroyed in the silo.

Infested cornstalks must be cut into pieces not longer than a half inch so that nearly all the borers may be killed. This precaution is particularly important if the silage is not placed directly in the silo or is not fed soon after it is cut.

If cutting and shocking in the field is done, the corn should be cut low and early. Low cutting also helps in doing a clean job of plowing later and makes other clean-up methods easier.

In general, the proportion of borers living in the stalk below any given height increases as the season advances.

If infested cornstalks are fed directly without previous cutting or shredding, the uneaten parts should be collected and destroyed unless they are trampled completely by livestock and thoroughly mixed with the manure of the feed lot.

Shredding or cutting corn fodder into fine pieces, as is ordinarily done by husking and shredding machines, kills 95 to 98 percent of the borers and makes the fodder more acceptable to livestock. Most of the borers that escape death in the machine perish during the general practice of storing the shredded material, feeding it to livestock, and using the residue as bedding, which is finally trampled into the manure.

Stalk cutters, which break up the stalks in the field, probably do not kill on an average more than 60 percent of the borers present, but they promote more rapid rotting of the stalks and make clean plowing easier.

EFFECTIVE PLOWING to control borers depends on turning under the corn remnants and other trash so completely that none of it remains on the soil surface. The material plowed under should not be dragged to the surface by later cultivation before the moths emerge, and the ground should be cultivated or pulverized to close all large cracks and crevices.

Plowing infested material under does not itself kill the borers. Most of the borers crawl up to the surface sooner or later. If the plowing has been clean, however, most of the larvae coming to the surface die because they are exposed to natural enemies like birds, ants, ground beetles, and insect parasites and predators. But if the plowing is not done clean, the borers, when they reach the surface, bore into any fragments of a corn plant or weed that may be left there and with that protection they can complete their development to the moth stage.

The depth of plowing for corn borer control is not important if all infested material is covered completely to such a depth that it will not again be brought to the soil surface by later cultivation or weathering and thus become a shelter for the borers that crawl on the surface. To insure proper coverage, however, and to reduce the possibility of the plowed-under material being again dragged to the surface, plowing to a depth of 6 inches or more should be done if soil conditions permit.

An effective plow attachment to aid in turning under trash consists of three No. 9 gage wires. The wires, about 12 feet long, are attached to the framework of the plow, and the outer ends are left loose. The loose ends are caught by the furrow slice as it is turned over. Thus the wires are held tightly to the top of the furrow slice by the weight of the soil on the buried ends of the wires and so turn all trash to the bottom of the furrow.

Disking cornstalks or high stubble in preparation for seeding to small grain or other crops is objectionable from the the standpoint of corn borer control, except when it is followed by clean plowing. Disking allows a very high percentage of borers to survive and the shade given later by the growing grain protects the borers in the trash left on the surface.

Rolling, soil packing, disking, or other similar types of cultivation are of practically no value in combating the borers.

INSECTICIDES are effective for protecting corn from damage by the borer.

Research has been directed toward finding more efficient and economical insecticides. In recent years nozzles have been developed and tested to deliver sprays with droplets of satisfactory size and under efficient pressures to be carried from the nozzles to the whorls, leaf axils, and other parts of the plants where the borers feed. Chemists have produced new and highly toxic insecticides and formulations have been modified to permit practical low application rates with freedom from nozzle clogging and with the ability to penetrate into the concealed plant parts where the larvae feed and to remain on the plants for several days. In the search for new insecticide material research workers have attempted to keep the toxicity to plants and warm-blooded animals as low as possible.