Some foods have been treated with this machine. The red color in meat often turned to dark purple when treated at room temperatures, whereas in such products as strawberries and carrots, a definite bleaching took place. These color changes were eliminated when the food was irradiated below 40 C. Tests have indicated that undesirable side effects could also be eliminated by evacuating the air around the object. Vegetables irradiated with overdoses of electrons showed a partial destruction of the cell walls and oozing-out of the cell contents.

We exposed some wood samples containing powder-post beetle larvae 3 to 7 months old to 1 and 2 impulses at a distance of 10 inches from the window and obtained 100 percent kill. This dosage was computed to be 145,000 and 290,000 rep.

Larvae of the confused flour beetle in an 8-mm. thickness of flour were exposed to one impulse on each side and all were killed. The dosage was computed to be 310,000 rep.

Complete mortality of the following insects resulted from similar treatment: American cockroach egg capsules, with a dosage of 350,000 rep; yellow-fever mosquito eggs, with a dosage of 600,000 and 900,000 rep; black carpet beetle larvae in 6 mm. of dog food, with a dosage of 310,000 rep; and bean weevil adults and larvae in one layer of lima beans, with a dosage Of 460,000 rep.

Codling moth larvae buried at various depths in apples were killed when at a depth of 6 mm. with a dosage of 70,000 rep, and when at a depth of 8 mm. with a dosage of 140,000 rep. Death of the codling moth larvae extended over 16 days at a minimum dosage, whereas with an adequate dosage the mortality occurred within several hours of treatment.

Potato tuberworm larvae at depths of as much as 1 cm. in whole potatoes were exposed to a dosage of 350,000 rep. This resulted in 100 percent kill of 5-day-old larvae, 95 percent kill of 3-day-old larvae, and 83 percent kill in 2-day-old larvae. The difference was thought to be due to differences in depth of the larvae in the potato. The 5-day larvae were found at a depth of 4 to 9 mm. where the maximum intensity of radiation would occur. The younger larvae were less than 4 mm. from the surface of the potato.

IN EXPERIMENTAL WORK it is often necessary to trace the insect or insecticide. This can be done by using some radioactive material such as triphenyl-phosphate, and taking readings with a Geiger-Muller counter. The counter can be used not only for tracing but also for determining the amount of insecticide in a particular area.

Radiant energy has been experimented with for detecting the presence of insects in material. When X-rays were projected through material containing insects, the insects could be detected under certain conditions on film.

Reports have indicated that material exposed to "black light," the shorter ultraviolet wavelengths, may cause fluorescence when the light is projected on insects, thus making it possible to detect their presence.

MALE SCREW-WORM FLIES have been sterilized by X-rays and then released with the hope that if this were done on a large scale the normal populations would be greatly reduced.

Many contraptions that supposedly use radiant energy for insect control have been given wide publicity. Some of them were probably meant to give satisfactory results, but the inventor was not familiar with the possibilities of radiant energy. Others probably were meant to fool the public. Some of these schemes have been investigated. One dubious machine was supposed to project various insecticides by means of radio waves. Another machine was supposed to kill insects in fruit by short impulses of high-voltage electric current. Insufficient time was allowed for heating and the method did not work, and arcing of the electric charges sometimes damaged the fruit.

SO, IN SUMMARY, the use of radiant energy for controlling insects is still in the experimental stage and will probably remain so for a long time.

Sound waves do not penetrate most materials that shield the insect. High-frequency waves are difficult to transmit through air, and low-frequency waves do not efficiently produce enough heat to kill the insect. High-intensity waves will shatter the insect and also injure most surrounding materials.

Radio waves kill insects by heat and also penetrate dielectric materials readily, but the cost of operation compared with other methods, such as vapor heat, makes them impractical to use at the present time.

Killing insects by heat produced by infrared waves is restricted not only by the cost of operation but by the poor penetrating qualities of this wavelength.

The chemically active ultraviolet rays have such poor penetrating qualities that their use for most insect problems is impractical.

The ionizing radiation used so far is either very inefficient, as with X-rays and gamma rays, or does not penetrate sufficiently without harming the commodity or material on which the insect lives. The most promising future application of ionizing radiation will be for producing more penetrating electrons or more efficient X-radiation. In any case the high initial cost of equipment must be considered.

THE SUCCESSFUL APPLICATION Of radiant energy is so dependent on a knowledge of the fundamentals of life and matter that both must progress together. The work with insects has opened up possible methods of control, however, and with the correlated work on mutations has added to the knowledge of life itself. It is hoped that, with the accelerated development of radiant energy equipment in recent years, increased interest will be shown in applying this energy to a study of insect problems.

ALFRED H. YEOMANS, a technologist of the Bureau of Entomology and Bunt Quarantine, has been engaged in investigating and developing equipment used in insect control. Some of his studies are concerned with such fundamentals as the effect of particle size, which must be considered when developing equipment. He is a native of California and a graduate of Ohio State University.