A rating is given to each county. It is based on the number of bugs present and the percentage of land under cultivation in the county. The reason for considering the percentage of cultivated land is that the greater the percentage of land that is farmed the less area there is to support protective cover for chinch bug hibernation and the fewer chinch bugs there will be in comparison to the crops that might be fed upon.

Having this information for infested counties, entomologists then proceed to plan their battle against the insects. They make estimates of needs for barriers for the next year on the basis of what would be considered the potential requirements. In doing so they realize that the hazards of prophecy are probably at their maximum when chinch bug infestations are being forecast and that weather conditions during the following crop season may produce an outbreak as serious as the potential or reduce the threat to noneconomic importance.

BARRIERS are used to protect susceptible crops from attack by bugs that migrate from small-grain fields. Three types of barriers are effective: Creosote line barriers, creosote paper barriers, and dinitro-o-cresol dust barriers.

A creosote line barrier is made by plowing a furrow with a moldboard plow around the field to be protected. The soil is thrown toward the corn. A narrow line of creosote is then poured on the smooth ridge of soil thrown up by the plow and on the side of the ridge toward which the bugs will approach. Post holes about 2 feet deep are dug in the trench next to the creosote line and several feet or yards apart. The spacing of the post holes depends on the abundance of the migrating bugs. Creosote repels chinch bugs. As they encounter the creosote, their direction of march is diverted as they seek to get around the line. They fall into the post holes, where they may be killed by pouring a small amount of kerosene or dinitro-o-cresol dust over them. Ordinarily I gallon of creosote is used for erecting and maintaining 1 rod of barrier.

The creosote-treated paper barrier is made by plowing a shallow furrow and digging post holes as for the creosote line barrier. A strip of tough paper 4 or 5 inches wide is placed against the vertical side of the furrow and the soil then tightly packed against the lower edge of the strip so it is in an erect position with the upper edge protruding 2 or 3 inches above the ground level. The paper used is cut and rolled and then thoroughly soaked in creosote. The Iowa Agricultural Experiment Station developed a machine for plowing the furrow and placing the paper at one operation. Farmers in Iowa and elsewhere have made similar machines. About one-half the creosote is required for a paper barrier as for a line barrier, but savings in the cost of creosote are more than compensated for in the cost of the paper and barrier construction.

Dinitro-o-cresol dust makes an effective barrier. It is prepared by mixing thoroughly 4 pounds of dinitro-o-cresol and 96 pounds of pyrophyllite dust. The mixed dust is applied in a strip 2 inches wide along the field that is being invaded. This barrier is easily disturbed by winds and the feet of animals. Its advantages are the saving of time in applying it and the fact that it kills the bugs that crawl through the dust in the barrier line. From 1 to 2 pounds of mixed dust is required to erect and maintain 1 rod of dinitro-o-cresol dust barrier.

Regardless of the kind of material used to construct a barrier, additional material must be applied to maintain an effective barrier for 10 days or 2 weeks or until the invasion ceases.

Direct control of chinch bugs by the application of sprays or dusts to infested crops may be practical now in some instances, using the newer insecticides. Insecticides have not been tested extensively against field-wide infestations, because infestations of chinch bugs have been nearly noneconomic since the chlorinated hydrocarbons became available.

Populations of chinch bugs fluctuate from year to year, as indicated by the fact that nearly 9,000,000 rods of barrier were constructed in 1934 and only 94,000 rods in the following year. Another year of high populations was 1940, when 2,221,000 rods of barrier were used to protect crops. After a survey in 1944, it was estimated that 7.5 million rods of barrier would be needed in 1945. Only 273,000 rods of barrier were constructed, however, because weather unfavorable to chinch bugs abruptly reduced their numbers.

CLAUDE WAKELAND is an entomologist in the Bureau of Entomology and Plant Quarantine.