Because the borer feeds in concealed places and because of the growth characteristics of the corn plant, application equipment differing greatly from that used on row-crop pests had to be. designed.

State agricultural agencies in most of the infested States have established services whereby the progress of corn and borer development is followed, and they can furnish reliable advice on timing of application, as well as on other problems relating to corn borer control.

Corn should be planted at the time which normally will allow it to produce its maximum yield in the locality in which it is grown as recommended by the State agricultural agencies. Avoiding early planting protects against heavy infestation by first-generation borers as well as the danger of poor germination and possibly frost damage in spring. Avoiding late planting protects against damage from second generation borers and from the possibility of early frost damage and soft corn in the fall.

No strain of corn has shown complete immunity from corn borers. Some strains have inherent characteristics that enable them to resist or tolerate the borers better than others. The number of borers per plant at harvest, as compared with the number of corn borer eggs originally on the plants, is much smaller in some strains of corn than in others. Also some strains of corn will stand up better than others under an attack by a given number of borers. Plant breeders are taking advantage . of the information obtained relative to the resistance of commonly used corn inbreds and those recently developed on the basis of borer resistance to provide growers with hybrids which can be expected to produce a satisfactory yield in the borer-infested localities.

Research to determine these points involved the study of thousands of lines of corn obtained from all parts of the world. Observations were made on such widely divergent material as open-pollinated varieties from Mexico and South America, areas in which corn was thought to have had its origin, open-pollinated corn grown for years under corn borer conditions in Europe, lines developed by breeders to provide resistance to other insects, germ plasm brought down from corn grown originally by the Indians in the United States, hundreds of lines developed by breeders searching for improved agronomic characters and many others.

In order to determine accurately the relative differences in resistance between the various lines of corn it was necessary that each should be infested with borers as nearly uniform as possible. To obtain this objective and to insure that tests could be made even in years of low natural borer infestation, many thousands of corn borer eggs are produced each year under laboratory conditions and placed on the test plants by hand. To promote the success and efficiency of this method many pieces of equipment and specific techniques were developed. Moths reared in large emergence cages are induced to lay eggs on wax paper. Egg-cutting machines capable of turning out 10,000 masses on wax-paper disks per day were utilized. Storage conditions for ovipositing moths and eggs were studied and improved in order to increase the efficiency of this research.

No one of the methods discussed gives all the control needed, but crop losses from corn borers can be cut by their use. The amount of benefit obtained will depend on favorable or unfavorable weather, how many of the control methods are used, and how well these are carried out.

While the grower has at hand means of saving his corn from serious injury, it should be the objective of research to reduce the threat so that no additional control methods would be necessary, other than those which would be followed in sound farm practice in the absence of the borer, or to reduce the cost in labor, money, and equipment of recommended control measures enough to promote their universal adoption.

To further the first of these objectives continued search should be made in all the corn-growing areas of the world to find and utilize germ plasm of high resistance to the borer. Incorporation of this material into agronomically desirable hybrids for use within the infested area would bring about substantial savings without seasonal outlays of funds for direct control measures.

Although the outlook for biological control seems encouraging, continued search should be made in those parts of the world where the borer is present but in which no investigations on parasites have been conducted. A more thorough study of predators and their utilization should be made and the role of such beneficial insects in the countries in which the borer is indigenous should be studied. An efficient combination of parasites, predators, and disease organisms would aid materially in reducing borer damage.

Research with respect to the second objective would involve the development of more efficient insecticides, application equipment, and application methods. More infallible and practical means of determining whether or not to treat and when to treat would be a distinct advance. Some studies have been made on systemic poisons. A number of systemic poisons have been tested both in the laboratory and in the field by mixing the materials in various dosages with the soil in which corn is grown. High mortality of larvae feeding on corn so treated has been produced. This work should be continued as it points to the possibility of a control measure which can be utilized with little additional cost to the farmer.

Wm. G. BRADLEY was entomologist in charge of the European Corn Borer Research Laboratory of the Bureau of Entomology and Plant Quarantine at Ankeny, Iowa. After graduation from Louisiana State University, he was assistant entomologist at the Louisiana Agricultural Experiment Station. In 1952 he went to the Dominican Republic to work on the Point IV program.