A recommended control measure is to dust the heads with DDT. In controlled pollination work, paper bags treated with a streak of aldrin give protection against the sorghum midge as well as the corn leaf aphid and the corn earworm, which attack sorghum when they are unusually abundant.

The earworm in particular is a corn pest that is becoming more of a problem on grain sorghum. Eggs are deposited on the leaves before heading and later on the peduncle and head. Feeding on leaves is comparatively minor. The larvae do most of their feeding on the developing grain; they devour kernels, sever lateral branches of the panicles, and create conditions for development of mold. Half of the seed often is destroyed.

THE SORGHUM WEBWORM (Celama sorghiella) is the moth stage of a somewhat flattened, hairy, greenish caterpillar, which sometimes attacks sorghum in the more humid areas. Newly hatched caterpillars feed on the flowers. When about half grown, the worms shift to the seeds and hollow out the kernels one by one. They spin a light amount of silk to attach themselves to the plant when they are ready to molt or when disturbed. Sometimes the worms become abundant enough to cover the heads. Half the crop may be destroyed.

The full-grown caterpillars spin cocoons on the plant and pupate. The whitish moths - that emerge from the cocoons dart about at night from plant to plant, laying their eggs one at a time on the sorghum heads. Because damage becomes more severe as the season progresses, early planting is suggested as a means of keeping down loss. The worms overwinter only on host plants; it is possible therefore to reduce populations by plowing under the crop leavings in the fall and burning off nearby areas of johnsongrass, the principal host plant of the web-worms, early in the season before sorghum attracts them.

THE ENGLISH GRAIN aphid (Macrosiphum granarium) and the apple grain aphid (Rhopalosiphum fitchii) feed on developing seed of small grain and cause blasting of heads. Both species attack the leaves in the fall and spring before active head growth. Reproduction is greater in cool weather. Parathion, methyl parathion, and tetraethyl pyrophosphate are used to control aphids. These materials are highly poisonous and should be used strictly according to directions.

INSECTS have caused little damage to rice in California.

In the Southern States, the rice stink bug (Oebalus pugnax) has been responsible for serious annual losses. Rice stink bugs overwinter, feed, and multiply on grasses and migrate to rice when it begins to head. They suck the juices from the developing seeds. Their feeding produces empty seed or pecky rice kernels that have discolored spots, which appear when the seed contents are only partly consumed.

Another sucking bug (Paromius longulus) causes damage similar to that of the rice stink bug but is of less economic importance.

The common chinch bug (Blissus leucopterus) has been observed in some places to cause direct damage to developing rice heads by invading fields after they are drained. The bugs feed on the plants at the nodes and under the leaf sheaths, and often cluster heavily just below the panicles, blasting them.

Aldrin, dieldrin, and toxaphene are used against the rice stink bug and chinch bug.

DDT AND the outstanding insecticides that have since been developed and marketed solved some of the vexing problems of insect control that faced seedgrowers one or two decades ago. There are indications, however, that these chemicals have not provided permanent solutions. Some insects that were remarkably well controlled in the 1940's developed measurable tolerances for DDT and several others.

Most of this resistance to insecticides in seed production has occurred in the Southwest. In the Salt River Valley of Arizona, sugarbeet seed of low quality reappeared in 1953. Experiments there in 1954 demonstrated that the residual action of DDT was no longer great enough to kill the nymphs of the lygus bugs that hatch after the DDT is applied.

Similar results were encountered in various localities on alfalfa and cotton. In Kern County, Calif., entomologists of the University of California found that lygus bugs taken from alfalfa seed fields became progressively more difficult to kill with DDT as the crop matured. By the end of the seed-crop period, the lygus bugs in seed fields were three to five times more tolerant of DDT than those in hayfields. They also found indications that nutrition may influence this change in susceptibility to DDT.

In later years, insect resistance to DDT has been met with additional applications or by substitution of other insecticides that provide better control.

In sugarbeet seed crops, for example, a second application of DDT or an application of toxaphene, benzene hexachloride, and dieldrin have been used.

Toxaphene, which kills better than DDT in warm weather, was substituted successfully on alfalfa for a time, but later in some localities tolerance for toxaphene also appeared.

Other insecticides under development in 1961 may meet this deficiency.

F. V. LIEBERMAN joined the Entomology Research Division of the Agricultural Research Service in 1929 as a scientific aid. Since his graduation from Iowa State University in 1936, he has studied western forage insect problems in Colorado, Utah, Montana, California, and Arizona.

F. F. DICKE is an entomologist with the Entomology Research Division and associate professor of zoology and entomology at Iowa State University. He joined the Department in 1927 and has been engaged in research on the biology and control of insects on cereal and forage crops.

ORIN A. HILLS is Leader of Western Vegetable Insect Investigations of the Department of Agriculture, at Mesa, Ariz.