Crops That Resist Insects

MANY A FARMER has seen the prospect of an abundant crop ruined by the onslaught of an insect pest that he was powerless to prevent. To make matters worse, nobody was able to tell him how to avoid like losses in the future. For years farmers, entomologists, and agronomists have wished and looked for crops or varieties that could be planted with assurance of freedom from destruction by one or another insect. It is, therefore, a pleasure to report material progress in the discovery and development of varieties of several different crops that have a high degree of resistance to certain insects.

Probably the most effective results to date have been achieved in the breeding of winter wheats resistant to the hessian fly.

Kawvale and Pawnee wheats were developed cooperatively by State and Department workers at the Kansas and Nebraska State Agricultural Experiment Stations. Both wheats carry a considerable degree of fly resistance and are in commercial use. The increase in acreage of Pawnee has been particularly rapid. Poso 42 and Big Club 43, two fly-resistant, soft white club wheats recently released in California, have given excellent performance in field plantings. Big Club 43 carries resistance to stem rust, bunt, and root rot, and a high degree of fly resistance.

Other promising fly-resistant varieties of hard red winter wheats for the West Central States and of soft red winter wheats for the East Central and Eastern States have been developed. They are highly resistant to the hessian fly and to several of the most serious fungus diseases.  The best of the strains are being tested for yield and quality, but are not yet commercially available.

Wheats resistant to the wheat stem sawfly have been developed. One, named Rescue and developed by Canadian workers, has been increased for distribution in sections of Canada and Montana, where the insect has caused heavy losses. Wheat varieties showing considerable resistance to the chinch bug have also been discovered by research workers.

Intensive work is in progress on the production of lines of corn resistant to the earworm, European corn borer, chinch bug, and stored-grain insects. Although the degree of resistance still found in corn to any of these insects has not been so great as that found in wheat to the hessian fly, results so far are promising. The commercial hybrid sweet corns Ieana and Golden Hybrid No. 10, for example, carry considerable resistance to the earworm. Several experimental lines of dent and sweet corn not yet commercially available are even more highly resistant.  They suffer only a tenth to a quarter as much injury by the earworm as the most susceptible lines and when crossed with lines having other desirable characters they can transmit earworm resistance to their progeny.

Studies have shown that earworm resistance is not all due to anatomical characters such as long, tight husks and flinty kernels. For some reason not yet understood the silks and kernels of certain strains do not appear to fill the dietary needs of the young worms and few of them become established. It is possible that much of the loss in corn yields caused by the earworm can be prevented through the use of earworm- resistant inbreds—which are still in the experimental stage—in the production of commercial hybrids. Earworm-resistant corn would be particularly valuable in the Southern States, where the insect is an important factor in growing field and sweet corn successfully.

Resistance in corn to the European corn borer appears to be of three types—unattractiveness to the egg-laying adult moths, inability of the young worms to survive, and ability of the corn to stand up and yield well despite infestation. Through the testing of hundreds of pedigreed lines, a few that have one or more of these qualities have been found.

Survival of first-generation borers in dent lines R4 and L317, for instance, is less than half of that in ordinarily susceptible lines. R4 and L317 have been used to some extent in the production of commercial hybrids. Another line, P8, has almost as good resistance to survival of first-generation borers and also stands up and yields well under the second-generation borers that attack corn late in the growing season.  This line has just been released for commercial use. About 30 lines of borer-resistant sweet corn, among which Yellow Bantam, Country Gentleman, and Evergreen types are represented, have also been found.  A few of them, such as Towa 45 and Towa 1445, are used in the production of commercial hybrids. The comprehensive corn breeding program now in progress seeks to find and produce commercially desirable lines of corn more completely resistant to the European corn borer and there is a fair prospect of eventually attaining this goal.

Work on insect resistance in other crops has been much less extensive than on corn and wheat. Nevertheless, striking results have already been obtained. Sorghum resistant to the chinch bug, barleys resistant to the green bug, alfalfa resistant to pea aphid and potato leafhopper, sugar beets resistant to the beet leafhopper, sugarcane resistant to the sugarcane borer, sunflower resistant to seed weevils, and even locust trees resistant to the locust borer are prominent examples. R. O. Snelling pointed out that the available literature includes records of resistance in nearly 100 plant species involving more than 100 insect species.

In almost none of the crops mentioned has it yet been possible to determine with certainty the particular characteristics responsible for the resistance. Thus, in the course of the breeding process, the only way yet found of selecting the resistant plants is to subject them to heavy infestation, usually by artificial means, since natural infestations cannot be depended upon to develop on all the plants. Testing and selection for insect resistance, in addition to all the other essential characters, further complicates the already difficult procedure of improving crop plants by controlled breeding.

Even with crops that can be put through one or more generations a year, the production of insect-resistant and otherwise satisfactory varieties is a long and slow process. Varieties that have the desired insect resistance must first be found by preliminary exploration. After that, many years of breeding may be necessary in order to transfer the resistance into varieties having the other characteristics, such as high yield, quality, and resistance to disease, that are essential to profitable commercial use. Despite these difficulties and others, accomplishments to date indicate that resistant varieties of crops offer one of the most promising means of solving many of the insect problems for which we have heretofore had no satisfactory solution.

THE AUTHORS
C. M. Packard is an entomologist in charge of the Division of Cereal and Forage Insect Investigations in the Bureau of Entomology and Plant Quarantine.
B. B. Bayles is an agronomist in the Bureau of Plant Industry, Soils, and Agricultural Engineering. Dr. Bayles is a graduate of the University of Wisconsin.
O. S. Aamodt is an agronomist in the Bureau of Plant Industry, Soils, and Agricultural Engineering, in charge of the Division of Forage Crops and Diseases.

FOR FURTHER READING
Snelling, Ralph O.: Resistance of Plants to Insect Attack, Botanical Review, volume 7, No. 10, pages 543-586, October 1941.

ALSO, IN THIS BOOK
Corn Hybrids for the South, by Merle T. Jenkins, page 389.
New Varieties of Wheat, by B. B. Bayles, page 379.
Improved Varieties of Barley, [***The Barley link won't work yet. -ASC***] by G. A. Wiebe, page 403.
More and Better Clover, by E. A. Hollowell, page 427.