TIMING the crop is the most successful cultural method used against insects. It is used in the production of clover seed to control the clover seed midge (Dasyneura leguminicola). This is a tiny, delicate, mosquito like fly that has a bright-red abdomen. It lays eggs on or near the flower heads of clover crops, principally red clover. The newly hatched larvae wriggle into the unopened flowers. They suck the sap from the ovaries and keep the ovules from developing. The seed crop may be heavily damaged or destroyed.

Development of the clover midge is closely correlated with weather and is particularly dependent on rainfall. Three generations are produced each year in the Northwest. The seed crop is grown from May to August; it is the summer generation of midges that damages it.

Control is effected by timing the appearance of the flower heads so that the midges find few suitable heads on which to lay their eggs.

Pasturing the field in the fall after the seed crop is harvested or in the spring before the seed growth is started will prevent most midges of the fall or spring generations from finding suitable flower heads. In consequence, the summer generation of midges will be small, and little damage will be done to the seed crop.

Clipping the spring hay growth for mulch about May 20 times the seed growth so that neither the spring nor summer generation midges find suitable flower heads.

If a hay crop is raised first, cutting and removing it promptly from the field in early June will kill most of the mature spring-generation larvae in the crop as well as time the blooming of the seed crop so that most summer-generation midges will have disappeared before the flowers become attractive for midge oviposition. It is important to remove the hay promptly because the mature spring-generation midge larvae, needing the moisture to move, will leave the flower heads for the soil and develop into adults if enough rain falls on the hay.

Another midge, Dasyneura gentneri,closely related to the clover seed midge, attacks Ladino and alsike clovers. It is less important than the clover seed midge, and no control has been developed.

Two tiny weevils frequently ruin seed crops of clovers. Tyshius stephensi is mainly a pest of red clover. Miccotrogus picirostris attacks white, alsike, and Ladino clovers. Both are gray and long beaked.

Like most weevils, they hide in winter in field trash or in heavy vegetation nearby. They become active in spring near their winter quarters. Often they feed on such plants as dandelion and wild strawberry. Later, when clover comes into bloom, the weevils move into the fields and feed upon the flowers. They lay one or two eggs in each young pod they encounter. Larvae hatching from these eggs devour most of the ovules. Both adults and larvae feed on the developing seeds, eating irregular holes into or through them. The larvae cause the greater damage.

DDT controls the seed weevils. The treatment must be applied after most of the weevils are out of hibernation but before many eggs are laid---about the time that 20 percent of the first set of blooms have turned brown.

Two other weevils, Hypera nigrirostris and H. metes, attack the heads and seeds of various clovers. The latter is particularly damaging to crimson clover seed in the Southeast. The larvae of both feed on the flowers, ovules, and growing seeds. The adults cause lodging of the heads by feeding on the stems. Control can be obtained by an early season application of aldrin, dieldrin, or heptachlor in granulated form.

THE VETCH BRUCHID is a little weevil that hollows out the seeds of hairy vetch. It ruined the production of hairy vetch seed in several Eastern States and then found its way into the Pacific Northwest and Midwest. It does not damage other vetches very much.

The bruchids lay eggs on the seed pods just after they are formed. Worms hatch from the eggs and bore into the pods from the underside of the eggshell without exposing themselves. They enter the green seeds and devour the contents. Each larva takes one seed. Each bruchid produces about 100 worms. They usually are abundant on hairy vetch and may destroy most of the seeds.

To control these weevils, a single application of DDT just as the pods begin to form is recommended. Because the bruchids congregate on the vetch for egg laying at that time, most of the seeds thus are protected. Bruchids survive in dry vetch seeds for months, but they do not feed on them.

MOST PRODUCERS of hybrid corn seed now have a well-planned insect-control program, which includes preventive measures, superior hybrid varieties, and insecticides.

Prominent among the pests of corn is the European corn borer (Pyrausta nubilalis). It is the larva of a moth that ordinarily has two broods or egg-laying periods annually in the major production sections of dent seed. The fully developed larvae are about an inch long. The first brood is more serious in causing loss of yield and chaffy seed in early planted corn. Early hybrids of sweet corn are subject to severe ear damage.

Planting early is a preferred farm practice in the production of dent corn seed. This practice facilitates processing the crop and is a safeguard against fall weather hazards. Well-timed applications of DDT, endrin, heptachlor, or toxaphene granules and DDT and endrin sprays can be depended on to control borers.

Late-planted or late-maturing corn is more likely to be damaged by the second brood, which becomes established in July and August. Worm survival is high on such corn, and about 50 percent of the infestation develops on the ear. Invasion of the shank and internodes above the ear cuts off the flow of nutrients to the ear. Direct injury to the kernels, with subsequent introduction of molds, lowers the yield and quality of seeds and makes costly hand culling necessary in the processing operation. Insecticides directed to the ear zone have given satisfactory results in protecting the ear against second-brood infestation.

Inbred lines have varying resistance to borers. It commonly is referred to as first-brood early leaf-feeding resistance. At least three resistant lines are required in a commercial hybrid to achieve effective resistance. Resistant hybrids are recommended and available for certain localities in the Corn Belt.

ANOTHER SERIOUS corn pest is the corn earworm, Heliothis zea. This moth larva destroys kernels and introduces molds to the ear. It is also known as the cotton bollworm and tomato fruit-worm. It is a pest every year in the South, where it has several generations, and periodically in the North, where it may have only one or two generations. The moths are attracted to the fresh corn silk for depositing eggs. As the young larvae hatch, they begin feeding on the silks and gradually penetrate to the kernels.

The fall armyworm (Laphygma frugi-perda) has feeding habits like those of the corn earworm on corn, but is of much less importance in the major areas of seed production.

Corn varieties differ in the husk qualities that protect the ear against damage by earworms. Through many years of selection, good husk protection is typical of southern varieties. Loose husks, characteristic of varieties in the Corn Belt, enable earworm larvae to damage the surface of the ear out of proportion to the actual grain destroyed.

For sections of the Central and Eastern States where seed is produced, early planting is desirable to avoid seed injury. Intermediate plantings are desirable in Southern States to avoid early and late season peaks in ear damage.

The rice weevil (Sitophilus oryza), which often follows earworms, enters the ears through holes the earworms make. Poor husk coverage and damage by birds or rodents late in the season also expose ears to field infestation by the rice weevil. Such infestation of standing corn is the principal source of populations that develop during storage.

Both adults and larvae of the rice weevil injure the kernels. Besides feeding, the adults eat out a cavity, usually one to a kernel, in which to lay each egg. Eggs laid in kernels that have higher than 65 percent moisture do not hatch. The larvae devour most of the contents of the kernels and then pupate within them. Adults emerge from the kernels a few days later, and the new females soon begin to lay eggs. The infestation may thus increase rapidly.

Entomologists at the Louisiana Agricultural Experiment Station reported that when harvest of corn is delayed in the South, up to 90 percent of the kernels may become damaged in the field. The rice weevil causes most of this loss, but other pests of stored grain, particularly the Angoumois grain moth (Sitotroga cerealella), cause some.

THE CORN LEAF aphid (Rhopalosiphum maidis) sometimes becomes a problem in seed production. It is known to overwinter only in warm climates on small grains and wild grasses. On corn, the colonies of small, green, soft-bodied plant lice escape observation in the early stages of development down among the whorl leaves. The farmer and seedsman usually see heavily infested plants, which have a sooty or reddish appearance, at about tasseling time or later. Then the damage has been done and plants often are partly or wholly barren.

Some inbred lines of corn are subject to barrenness. Other lines are attacked only lightly and show little effect on yield. Insecticides, as they have been used against the aphids, have not prevented barrenness.

Pollination in corn sometimes failsas a result of persistent feeding on the emerging silks by certain insects. The commonest are adults of the northern corn rootworm (Diabrotica longicornis), the southern corn rootworm (Diabrotica undecimpunctata howardi), the Japanese beetle (Popillia japonica), and several species of grasshoppers. All are attracted to fresh silk and congregate in their feeding long enough to interfere with pollination.

The sap and fungus beetles (Glischrochilus q. quadrisignatus and species of Carpophilus) often infest corn. These little black beetles are attracted to fermenting plant wounds, such as the entrance holes of the corn earworm and the European corn borer in corn. Sometimes they enter ears with loose husks without the aid of these worm tunnels.

The beetles will displace and even incidentally kill borers in the ear or stalk. They may lay eggs on the decaying plant tissue. The larvae of Carpophilus beetles sometimes hatch and feed among the kernels. Adults usually feed in worm-damaged areas and cause ear rot molds to spread. Their net effect on seed corn sometimes is considered beneficial because their presence causes the more destructive earworms and corn borers to abandon their burrows.