Poisonous dusts are effective regardless of the moisture content of the seed. Because surplus seed stocks often are fed to animals, however, the dusts have not been popular. Outstanding among them are lindane and DDT. Lindane is effective at a dosage of 1 part per million and DDT at the rate of 15 parts per million. Both are best used in combination with a carrier such as pyrophyllite or similar chemically inert dust. The carrier increases the volume and therefore insures thorough distribution over the seed. A dust containing 3 percent of DDT is effective when mixed with seed at the rate of one-half ounce per bushel. No damage to seed viability has been observed as a result of treatment with either compound at recommended dosages.

The practice of treating many types of seed with disinfectant dusts to protect it from fungus diseases is being amplified by the incorporation of small percentages of DDT to insure protection from insects.

Dusts may be applied by any method that will insure a uniform coverage. To treat bulk seed, a seed-treating machine is satisfactory. Operators applying the dusts should be equipped with adequate respirators. Because of the poison hazard involved, seed that has been treated with DDT, lindane, or a fungicide should not be used as food for man or livestock.

Grain is transported to mills and terminal elevators chiefly by railways. Boxcars used for the purpose are so constructed that grain and grain dust invariably accumulate in cracks in the floor, at the junction of the walls with the floor, between the ends and the wooden-end linings, and sometimes between the side walls and the inner grain linings of the cars. Such accumulations of grain and dust become infested, and the infestations are difficult to remove or destroy by ordinary methods. Consequently they are dangerous sources of infestation to other, later shipments of grain or milled cereal products. Obviously it would be desirable to prevent the contamination of the cars by shipping only insect-free grain or other products. While much is being done to reduce infestation in grains and grain products, it is doubtful whether we shall ever reach the stage where total elimination of insect infestation in these products will be possible.

Changes in the construction of boxcars would help reduce the opportunities for insect colonies to become established in them. The removal of the bottom board on the inner grain linings on the sides of the cars facilitates cleaning and prevents the accumulation of grain and waste material between the linings and the side walls. The placing of layers of resilient insulating material between the end linings and the corrugated ends of the cars would help eliminate space in which grain and dust could accumulate. Fibrous glass shows promise of being useful for this purpose. The impregnation of such insulating materials with DDT would probably add to their efficiency in preventing the establishment of insect infestations.

As remedial measures where infestations do occur, cars should be thoroughly cleaned out with compressed air after each use. The application of a residual spray (with a knapsack sprayer, a power sprayer, or an aerosol-type generator) also is helpful. Residues from it do not appear to be a hazard to shipments of grain or milled cereals. In most cases, cars are lined with paper before loading with milled cereals.

GRAIN AND GRAIN PRODUCTS are so attractive to insects that they have to be packaged in containers that afford them the greatest protection from infestation during later storage.

Most insects that infest cereal products have comparatively weak mouth parts and cannot cut through substantial wrappers. Many can thrust their ovipositors through the meshes of fabric bags and lay their eggs directly in the cereal products within the bags. The immature stages of many insects also can crawl through the meshes and through needle holes along the seams and at the top or bottom where the bags are sewn. The more closely woven fabrics offer the greatest resistance to penetration. Bags made of paper, paper laminated to cloth or back-filled fabrics, and cartons of fiberboard offer more resistance to insect penetration than ordinary cotton or jute bags. Unless such containers are adequately sealed, however, small flat beetles, such as the saw-toothed grain beetle and the larvae of other beetles and moths, may easily penetrate through minute openings where the seals are imperfect. Most commercial methods of sealing bags and cartons are inadequate. If bags are closed by sewing, the sewed ends must be protected by the use of a gummed strip that will cover all needle holes. For fiberboard cartons the application of a wet-wrap cover offers the best protection. Experimental work with insect repellents for incorporation in the adhesives used to seal fiberboard cartons and paper bags may help solve the problem.

Impregnation of fabric and paper bags with pyrethrins or pyrethrins and synergists has been found to afford considerable protection against penetration by insects. In fabric bags this protection is more efficient when the weave is close enough to offer some mechanical resistance against penetration. More powerful insecticides such as DDT, benzene hexachloride, and chlordane also are effective in resisting penetration when used to impregnate bags, but (because of the danger of contaminating the food) are not practical for use in insect-proofing bags intended for packaging food. Insect-repellent chemicals may offer the best means of providing an insect-proof container. Packages impregnated with them are particularly useful in resisting the invasion of certain insects that have wood-boring habits.

The cadelle, probably the most troublesome of the boring insects, feeds on a wide variety of stored commodities and is widely distributed. It is primarily a pest of grain and flour and is commonly found in railway boxcars, ships, warehouses, farm granaries, and other places in which foodstuffs are stored or transported. The larva bores into woodwork to form a sheltered place in which to hibernate or to transform to the pupal or adult form. It has jaws powerful enough to cut through many types of packages. It will cut through a multiwall paper bag or metal-foil-wrapped carton overnight.

Termites also burrow through cartons and other packages that are stored in warm, damp locations, or in warehouses with wooden floors that are infested. The larvae of many insects, when fully grown, have the urge to migrate in search of pupation quarters.

THE STEADY RISE of population in this country and the increasing demand placed on us to share our food supply with people of other nations makes it imperative that we conserve as much as possible of our harvested crops.

More pest-free storage, on and off the farm, is needed for handling crops at harvesttime and to carry over reserves from year to year.

We cannot in the foreseeable future expect research concerned with the control of insects in stored grain to be completed, but on the other hand, we are more than holding our own against these pests. As we learn more and more about sprays, fumigants, control of grain moisture, and the habits and weaknesses of the insects themselves we are better able to meet their threats.

R. T. COTTON has been an entomologist in the Bureau of Entomology and Plant Quarantine since 1919 and has been in charge of field research on the control of the insect pests of stored grain and milled cereal products since 1934. He has specialized on fumigation and other methods of controlling the insect pests of stored foodstuffs. Dr. Cotton holds degrees from Cornell University and George Washington University. In 1940 he was given a Modern Pioneer award in recognition of achievement in science.

WALLACE ASHBY, a native of Iowa and graduate of Iowa State College, is an agricultural engineer in charge of research on farm buildings and rural housing in the Bureau of Plant Industry, Soils, and Agricultural Engineering.