Other promising results obtained with DDT are :

In bait preparations for control of the armyworm. (Cirphis unipuncta (Haw.) infesting small grains and the fall armyworm (Laphygma frugiperda (A. & S.) attacking field corn.

In dusts and sprays for control of the tobacco thrips (Frankliniella fusca (Hinds) on seedling peanuts, the potato leafhopper Empoasca fabae (Harr.) on alfalfa and peanuts, and the velvetbean caterpillar (Anticarsia gemmatilis (Hbn.) on peanuts and velvetbean.

In dust mixtures against the rice stinkbug (Solubea pugnax (F.), the lespedeza webworm (Tetralopha scortealis (Led.), and a grassworm (Pachyzancla phaeopteralis (Guen.) on lawns.

In sprays for control of the corn flea beetle (Chaetocnema pulicaria (Melsh) on sweet corn. Further experimentation is needed to develop effective formulations, dosages, and methods of application that will not leave dangerous residues, before DDT can be recommended for control of any of these insect pests.

Besides DDT, a number of other synthetic organic compounds have been tested in preliminary experiments against insects attacking cereal and forage crops in the field with varying results.

Benzene hexachloride, the most promising of these, has been found to be highly effective against grasshoppers, the white-fringed beetle, the sugarcane borer, and the rice stinkbug, and somewhat less effective against the European corn borer.

A DDT analog, di (p-methoxyphenyl) trichloroethane, was found tc be comparatively ineffective against the European corn borer, fairly effective against the white-fringed beetle, and much more effective against grasshoppers than DDT.

Piperonyl cyclohexenone in a spray suspension was very effective against the European corn borer, but alone or in combination with pyrethrins in spray and dust preparations it had little value as a contact insecticide against the chinch bug.

TDE, or 1,1-dichloro-2,2-bis (p-chlorophenyl) ethane, in emulsion form was found to compare favorably with DDT when atomized onto the silks and husks of sweet corn for control of the corn earworm.

Among the plant materials that have recently received increased consideration as insecticides, ground sabadilla seeds and ground stems of Ryania speciosa have been of particular interest. Both sprays and dusts containing Ryania have been effective against the European corn borer in sweet corn. They have given better control than recommended rotenone preparations and practically as good as preparations containing DDT. Ryania has also been found to be highly toxic when used as a contact insecticide against the chinch bug, although heavy dosages were required to produce a high rate of mortality under field conditions. Used as a dust mixture applied to 3- or 4-day-old sweet corn silks, however, Ryania gave no control of the corn earworm.

As with Ryania, good control of chinch bugs in small grain and corn has been obtained with heavy single applications of dust containing 5 to 20 percent of sabadilla. Minimum effective dosages of this material against the chinch bug have not been determined in our experiments.

Observations on the effects of the various materials I have discussed have shown that, with only a few exceptions, none of them has affected plant growth adversely, whether applied as sprays or dusts, or as foliage or soil treatments against cereal and forage crops in the field. None caused any plant injuries when applied to foliage, but DDT has been observed to injure rye and tomatoes planted in sandy soil that had been treated with 10 pounds or more of technical DDT per acre mixed with the top 3 inches of soil. Also, plant injury has been observed in rice, cow-peas, and oats growing in light soil containing 10 pounds or more of the gamma isomer of benzene hexachloride to the acre, mixed thoroughly with the top 3 inches of soil.

THE AUTHOR

W. A. Baker, an entomologist in the Bureau of Entomologly and Plant Quarantine, was appointed assistant leader of the Division of Cereal and Forage Insect Investigations in 1943. Before that he investigated insects and their control in the field, particularly cereal and forage insects in the Southwest, the European corn borer, and the utilization of parasites in the control of the gypsy and brown-tail moths and the European corn borer in New England and the Midwest.