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A small metal cylinder, baited with an extract prepared from the last two abdominal segments of female gypsy moths, is highly attractive to male Radiant gypsy moths. The cylinder has a rim at each end to w^hich is attached a and Insects screen cone in which there is a hole for the moths to enter. A sticky paper Alfred H. Yeomans lining prevents their escape. The use of the extract from two tips per trap will catch male gypsy moths, but the Radiant energy can be applied in extract from 15 tips is necessary to at- uncounted ways to kill insects. To tract the maximum number. The ex- prevent damage in storage and the tract is dispensed on a corrugated transportation of pests into quaran- paper roll suspended by a wire inside tined zones, it has been tested on fruits, the cylinder. The traps are not prac- potatoes, grains, wood, textiles, and tical for control, but were used in sur- perhaps other commodities. It has been veys of approximately 7 million acres used to kill larvae of mosquitoes in for the presence of the gyjosy moth in water. The aim is to kill the insect New England, New York, New Jersey, without harming the material on which and Pennsylvania in 1950 and again in it lives and to do it economically. 1951- Radiant energy includes of various —such as THE INTERP:ST in traps remains at a radio, , visible and high level and efforts to improve their , X-rays, and gamma rays. It in- effectiveness and extend their range of cludes waves of various wave- usefulness continue. The day may lengths, such as audible and ultrasonic. come when traps will be devised that It includes also the energy from various are greatly superior to those we now atomic particles such as neutrons, have; the effort to develop them will alpha, and electrons. be worth while. Its action depends on the structure of matter. All matter, including insects, HOWARD BAKER is assistant leader of is made up of combinations of some of the division of fruit insect investiga- the 92 basic elements. Each basic ele- tions. Bureau of Entomology and Plant ment comprises a particular type of Quarantine. He was graduated from electric called an atom. the University of Massachusetts in The systems themselves are composed îg2S and joined the Department im- of elementary particles, some of which mediately thereafter. After various have no electric charge or . Two field assignments on apple and pecan of the particles, the protons (which insects in the East, Middle West, and have a positive electric charge) and South, he was transferred to Washing- the neutrons (which have no electric ton in ig44. charge) comprise the basic mass of the T. E. HiENTON is in charge of the atomic nucleus. The number of pro- division of farm electrification, Bureau tons determines the type of atom of Plant Industry, Soils, and Agricul- formed. The nucleus is surrounded at tural Engineering. Between ig2^ and a relatively great distance by negatively ig^i he was in charge of farm electri- charged electrons having a definite pat- fication investigations at Purdue Uni- tern. Normally the number of electrons versity, where he conducted research equals the number of protons in the on the development of farm electrical nucleus. Atoms can be combined chem- equipment. Dr. Hienton holds degrees ically into various patterns of electrical from Ohio State University, Iowa State solar systems, or molecules, that form College, and Purdue University. the various materials as we know them. 411 412 Yearbook of Agriculture 1952 Living organisms comprise such com- The discovery that ultrasonic sig- plicated patterns of these molecules nals sent through water killed fish and that we do not know everything about destroyed other marine life led to re- their make-up. Nothing is known of the search on the effect of ultrasonics on substance that gives life to the com- biological organisms. Many types of bination of molecules forming living organisms have been exposed to vari- organisms. ous and intensities. Fish The energy contained in one atom is and frogs were easily killed, and some tremendous for its size. Some types of insects and bacteria were destroyed. atoms can be broken apart and their Some of the effects of ultrasonics on energy released, such as the explosion biological organisms have been clearly of the atomic bomb. The electric solar explained. Others have been explained system of the atom may also be changed only partly. The biological effects may less drastically. Radiant energy in vari- be due to generated by the sound ous forms and intensities is the means waves or, when the energy is intense, to employed to do so. Radiant energy may the shattering or tearing apart of the be used to increase the natural vibra- organism. Less apparent effects are tions of the atoms and molecules. The probably due to chemical changes. result is increased temperatures of the The use of sound waves for most in- material. It may be used to cause chem- sect-control purposes is impractical be- ical combinations of atoms that are re- cause of the inefficiency of low-fre- luctant to combine. Molecules also may quency waves and the difficulty in be struck with enough energy to break transmitting high- waves off electrons and leave fragments called through air. The high-frequency ions. equipment available in 1952 could be The molecular structure of an insect used only in laboratory tests. Even is so complex that when radiant energy when a specimen can be exposed in is applied it is difficult to determine liquid, the high reflecting and absorb- which factors or combinations of fac- ing qualities of materials shielding the tors cause its death. Each type of radi- insect make this method of controlling ant energy results in a predominant all but exposed insects impractical. action on the molecule, however. Sound is a mechanical force pro- When the energy is intense enough, the duced by rapid vibration in some insect is killed because it is torn apart medium, such as air or water. It travels physically. in the form of waves. Sound waves have three major dimensions, fre- THE USE OF HIGH-FREQUENCY or quency, velocity, and . ultrasonic sound waves, other than the The frequency is expressed in cycles audible ones, is a relatively new or vibrations per second. One kilocycle science. The first on it was done (kc.) is 1,000 cycles per second. Fre- in about 1900. Until the First World quency and pitch are identical in most War it remained a laboratory study, respects; the notes of the musical scale in which small tuning forks, sparks, are defined in terms of frequency. The and special whistles were used to pro- human ear registers sound from about duce the waves. During the war, a nar- r6 to 20,000 vibrations per second. row beam of high-frequency sound Beyond that is ultrasonic sound. The was used to detect submarines. Since highest frequency so far attained is then it has been used for underwater 500 million cycles. signaling, testing for flaws in materials, The velocity of sound waves is deter- and removing smoke. It has been used mined by the medium in which they experimentally in television, medicine, travel. Sound travels about 1,000 feet , and metallurgy. It helps in per second in air and about 4,800 feet the agitation of solutions and in mak- per second in water, depending mainly ing some chemical reactions. on the temperature. Radiant Energy and Insects The can be determined When sound waves travel from one by dividing the velocity by the fre- type of medium into another, part of quency. In air^ at a frequency of 1^126 the energy is reflected back into the cycles per second, the wavelength is first medium. The amount reflected about I foot. At 1,000 kilocycles, the depends on the density of each ma- wavelength in air is about 0.0344 terial and the velocity of sound. In an inch and in water about 0.145 inch. air-solid boundary, practically 100 per- The cathode-ray oscilloscope is used cent of the energy is reflected. for making sound waves visible so that When a sound wave meets an ob- they can be studied. stacle, the amount of de- The intensity is the amount of pends on the size and shape of the energy in the sound wave. A piano key object. If the object is small compared struck violently or softly produces the to the wavelength, some of the wave same number of vibrations per second tends to bend around the object. When but with different intensities. Since it sound waves strike an object at an is the energy that does the work, the angle, a certain amount of the wave is most effective sound machine is the refracted and the rest is reflected. In one that can put the most into liquids and solids, when the angle of the vibrations it emits. Intensities at incidence is greater than about 15 de- low frequencies are measured in deci- grees, all of the wave is reflected. bels and otherwise in per square Thin plates may or may not conduct centimeter. There arc several instru- sound waves, depending on their di- ments for measuring the energy in a mensions and physical properties. sound wave, but it is difficult to obtain The hard shell of some insects, such a high degree of accuracy in the as adult roaches, has high reflecting measurements. qualities that are difficult to overcome. The greatest damage to insects is When the is intense caused by sound waves having a fre- enough to cause shattering of the cells quency that produces the maximum of the insect, the maximum bursting absorption in the insect but the mini- action perhaps is obtained by wave- mum in the surrounding materials. lengths shorter than the cell but long The amount of absorption has been enough to produce natural resonance. found to increase with the square of That would cause the maximum in the frequency of the sound wave, and pressure on different parts of the cell with the viscosity and heat conduction at the same . Gas bubbles may of the material. The absorption of form which burst with tremendous energy in air is quite high compared pressure and disrupt the organism. to that in water. One of the earliest practical ultra- L. Bergmann, the German physicist, sonic generators was based on the dis- gives the following values for the dis- covery by Pierre and Jacques Curie in tance in air and water in which the 1880 that a specially cut quartz crystal, sound intensity is reduced to one-half. when subjected to pressure and tension, will develop electric charges on its 10 kc. 100 kc. 1,000 kc. crystal faces. Later it was found that Air .' 220 m. 220 cm. 2.2 cm. Water. . . . 400 km. 4 km. 40 m. this is reversible and that the crystal will expand and contract, thus produc- The absorption in solids depends on ing sound waves when an alternating the grain or fiber structure of the ma- voltage is applied to the surface. It is terial. Such fibrous materials as cotton possible to amplify the vibrations or glass wool have high absorption greatly by cutting the crystals properly values. and backing it in such a way that The generation of heat at the bound- resonance or natural vibrations am- ary surface of two substances traversed plify the waves. The crystal can also be by ultrasonics is especially strong. cut concave to focus the waves. A con-

070184°—52- -28 414 Yearbook of Agriculture 1952 cave crystal has been found to be more ranged so that the frequency can be efficient than a fiat one. At the focal changed by changing the transducer point of converging sound waves, the unit. energy is as much as 150 greater The siren type of sound generator is than at other points. The crystal ultra- used to produce low-frequency sound sonic generator is called the piezoelec- waves in air. It is not so efficient as tric type and is widely used to produce the m¿ignetostriction or piezoelectric frequencies above 200 kilocycles. With type, but it can handle a large amount special crystal rods they can also be of and the fre- •made to produce lower frequencies. c]uency can be changed by changing Because of the , this the speed of the rotor. type of generator is not used to gen- A number of exploratory tests of the erate ultrasonics in air or other gases. use of ultrasonic waves on insects have The part of the generator that converts been made at the Agricultural Re- the electrical energy to sound waves, search Center at Beltsville, Md. A the transducer, is submerged in trans- piezoelectric type of generator, an Ul- former oil, from which the sound waves trasonerator, model SL 520, was used. are transferred to the testing medium. It has four transducer assemblies, each Another method of producing ultra- designed to produce a fixed frequency. sonic waves is with the magnetostric- The frequencies available are 400, tion type of generator, w^hich produces 700, 1,000, and 1,500 kc. Wc used the sound waves by the magnetization and 400 kc. The maximum power input demagnetization of a metal rod. When was 300 milliamperes (ma.) and 1,800 some metals are magnetized and sub- volts or 540 watts. Other tests were run jected to tension and compression, a at 200 milliamperes and 1,250 volts or voltage is induced in a surrounding about one-half power. Because of var- coil. The process is reversible ; by mag- ious losses, only about one-half the netizing the rod by one coil and im- input power could be applied to the pressing an alternating voltage on specimen. It is hard to expose test sam- another coil surrounding the rod, ul- ples to the sound waves without shield- trasonic waves can be generated at the ing out a good part of the energy with end of the rod. The waves generated the materials used to hold the samples. depend on the frequency and magni- Standing waves usually are set up tude of the applied voltage. Nickel or in the enclosure in which the gen- nickel alloy are usually used. To be erator is operating. The position in efficient the rod must be designed which the sample is placed in relation properly to utilize resonance in ampli- to the standing waves is important. fying the waves sent out. A circular The crystal and other parts of the plate is usually attached to the end of transducer are housed in a battery jar the rod to act as a radiator. The elec- containing about 12 liters of trans- trical circuit can be very simple. At low former oil. The quartz radiates the ul- frequency it is possible to get large trasonic weaves upward through the amounts of energy from this type of transformer oil into a very thin copper generator. At high frequency it cannot cup, 3 inches in diameter and 3 inches be tuned sharply and it is too sensitive deep, which contains circulating wa- to temperature. The magnetostriction ter. The test samples were suspended generator usually is used for frequen- in the water-cooling cup. In the piezo- cies of 5,000 to 60,000 cycles. At that electric and magnetostriction genera- frequency it can be used to generate tors operating in liquid, heat is pro- sound waves in gases and liquids. Mag- duced in the liquid by the conversion netostriction and piezoelectric genera- of electrical to mechanical vibrations tors operate on a fixed frequency, with as well as by the absorption of the the intensity varying with the applied sound waves. Since the effect of tem- electrical energy. They are usually ar- perature is fairly well known in ento- Radiant Energy and Insects mology, the first tests were made to 100 percent at 30 minutes. No wax learn the other efifects of uhrasonics. was visible on the dead or dying That was done by maintaining the cir- aphids, but the surviving aphids had a culating water at a constant tempera- normal waxy coating. Probably the ture. However, temperature seems to latter were protected by air bubbles. modify other efifects of ultrasonics and There seems to be some direct corre- should be later explored. lation between the mortality and the We tested newly hatched codling apparent absence of wax on the aphids. moth larvae. We tried several means of Bean aphids on bean leaves were holding them. Paper extraction thim- similarly exposed. A direct correlation bles or filter paper shielded them too was found between the mortality and much. Better results were had when the protection of the aphid by air bub- the larvae were exposed in small glass bles. All aphids that were thoroughly vials containing water. In one series wet were killed, and many of them of the latter, when the temperature were bloated. was maintained at about 17° C, and Two-spotted spider mites were also the power at 300 ma. and 1,800 volts similarly exposed. They. were more with a 400-kc. frequency, the mortality thoroughly wet than the aphids and varied from 100 percent at 40 seconds more than 90 percent were killed at to 25 percent at 10 seconds. exposures of 4 to 30 minutes. Some of When the temperature was increased the dead mites were flattened out as a to 20° C, the mortality varied from result of the ultrasonic waves. 70 percent at 5 seconds to 50 percent Third-instar -fever mosquito at 2 seconds. When the power was re- larvae were exposed to ultrasonic en- duced to 160 ma. and 1,100 volts and ergy with a frequency of 400 kc. At a a temperature of 20° C, the mortality power of 300 ma. and 1,800 volts, the was zero at 5 seconds exposure. larvae were all killed at exposures of Codling moth larvae in apple plugs 7 seconds at 25° C. to 9 minutes at 42°. scaled with wax in test tubes were ex- Many of the larvae were eviscerated posed to 400-kc. ultrasonic waves at after exposure of 3 minutes or more. 200 ma. and 1,250 volts, and at 300 With a power of 200 ma. and 1,250 ma. and 1,800 volts, and there was no volts the larvae had a mortality of 92 mortality when exposure was 15, 30, percent after 2.5 seconds exposure at 60, or 120 seconds. When the wax was 22.2° C. and 100 percent after 20 sec- not used, there was still no mortality onds exposure at 23.5°. When the when exposed for 10 minutes at 17° power was further reduced to 100 ma. C. or I hour at 20°. Codling moth and 750 volts, varying the exposure eggs, on paper and i to 4 days old, from 2.5 to 20 seconds did not seem were exposed in the water testing me- to afifect the mortality, which was dium to ultrasonic waves at 400 kc, about 35 percent at 21.5° C. 300 ma., and 1,800 volts with exposure In previous tests on adult yellow- times up to 120 seconds. About 30 per- fever mosquitoes, in which low-fre- cent failed to hatch, as compared with quency sound waves in air produced 14 percent of unexposed eggs. by a siren-type generator were used, Cabbage aphids, with the usual there was no apparent efifect on the waxy coating, were exposed on small mosquitoes at frequencies of 100 to sections of cabbage leaves. The wet- 21,000 vibrations per second with an ting agent, sodium lauryl sulfate (i- energy of 2 watts nor any ill efifect at Ï 0,000), we used did not entirely pre- 13,000 and 21,000 vibrations per sec- vent the formation of air bubbles on ond at 100 watts energy. The mosqui- the leaves. A frequency of 400 kc. and toes were exposed in 20-mesh copper- a power of 300 ma. and 1,750 volts screen cylindrical cages 2 inches in were used. The mortality varied from diameter and 7 inches long. 62 percent at 4 minutes exposure to Various investigators have studied 4i6 Yearbook of Agriculture 1952 the made by insects. Many of major dimensions, frequency, velocity, them can now be accurately repro- and intensity. duced. It has been suggested that the The frequency is the cycles per sec- sounds could be used to attract insects ond in which a field changes from an so they can be destroyed. electric through a magnetic and back to an electric field. One kilocycle equals RADIO WAVES have been used since 1,000 cycles per second, and one mega- about 1928 in a number of studies of cycle equals i million cycles per sec- insects. Most of the work has been with ond. limited power and range of frequen- The velocity of electromagnetic cies. The effect of the radio waves on waves in a vacuum is about 300 million the insect seems to be mainly due to meters per second, which is said to be heating. In experiments on bacteria, in the speed of light. The permeability which heat was removed as rapidly as and dielectric constant of the material it was generated and the temperature through which the waves travel aíTect could be kept below the thermal death the velocity. point, there was some evidence that The wavelength is a function of fre- high-intensity electric fields could kill quency and velocity. In free space, the without heat. Because heating would wavelength in meters can be computed normally first kill the organisms from by dividing 300 million by the fre- these high intensities, radio waves have quency. been used only as a means of heating to A field of high-frequency radio the temperature required for the death waves is more useful in heating poor of the insect. For practical purposes, conductors of than in heat- heating with radio waves must be ing good conductors such as metals, cheaper than the simpler heating meth- which are affected mainly near the sur- ods, much faster, or less harmful to the face. If heating of good conductors commodity. In order to use and evalu- by electricity is desired, it is more ef- ate radio waves for insect control, some ficient to run alternating current of their properties should be known. directly through the conductor or to Electromagnetic waves, which in- induce an alternating current in the clude radio waves, can be classified ac- conductor by surrounding it with an cording to their wavelength. The audio alternating current. waves useful in converting electrical Heating nonconductors (dielectrics) to audible sound waves have a wave- in a field of high-frequency radio length longer than 20,000 meters. The waves is usually done in an oven whose radio waves useful in transmitting en- top and bottom are condenser plates. ergy over long distances have a wave- Oscillating tubes are used to activate length of 20,000 meters to about i one plate with a positive charge while centimeter. Infrared rays have a w^ave- the other is negatively charged and to length from i centimeter to about i reverse this charge with any frequency micron ; visible light rays from i micron desired. With proper design, an effi- to 4,000 angstrom units, each color cient field can be established when having its own wavelength band; ultra- specimens are inserted between the from 4,000 to 300 angstrom plates. To be efficient the frequency units; X-rays from 300 to i angstrom must be such that standing waves are units; and gamma and cosmic rays not formed on the plates or in the below I angstrom unit. specimen. Also, the plates must be Electromagnetic waves are simply shaped to prevent edge efiPects, and the traveling fields in which the energy specimens must establish a uniform alternately varies between an electric dielectric constant between the plates. and a magnetic field. These waves can The intensity of the field in radio be projected through a vacuum and, waves is given in volts per centimeter. like other wave forms, have three The permissible voltage across the Radiant Energy and Insects 417 electrodes in dielectric heating is lim- by most materials so that the penetra- ited by the dielectric strength of the tion is not so deep as with radio waves. material, which sometimes changes The usual method of producing infra- with frequency and temperature. rays is by means of the red incan- When moisture is present steam may descent bulbs that are widely used as be generated. If the conductivity of heat lamps. In some commercial appli- the material is such that arcing occurs cations for heating grain to kill insects, when high voltages are applied, the the loose grain has been carried on arcing will char the specimen. belt conveyors between banks of infra- The heat generated in a dielectric red lamps both above and below the specimen placed in an electromagnetic belt. In this way the grain is quickly field can be computed when certain brought to the required temperature electrical properties of the specimen to kill the insects infesting it. are known. The properties can be measured but differ in various ways VISIBLE LIGHT RAYS have been used with the frequency of the electromag- to attract insects so that they could be netic waves and the temperature and trapped and destroyed. No other effects moisture content of the specimen. have been found that could be used in Those factors cause each type of ma- insect control. They are produced by terial to have an optimum frequency the common incandescent or fluores- for efficient heating as well as an opti- cent light bulbs giving a wide range of mum frequency for producing a strong wavelengths of relatively low intensity. field without arcing. Heating has been Light and ultraviolet rays. X-rays, and found to vary directly with the square gamma rays are thought to be of the field intensity and with the first resulting from the collision of two power of the electrical properties of atomic particles, the electron and the the material. positron. The investigations of high-frequency radio waves of insects have shown that ULTRAVIOLET RAYS, which have vari- when the insects are imbedded in Hour, ous effects on biological organisms, grain, or similar material no noticeable usually are produced by means of the selective action occurs on the insect. mercury arc enclosed in quartz. This That is probably due to the conduc- produces wavelengths from about tion of heat either to or away from the 2,400 to 4,350 angstrom units. Most of insect as the temperature varies be- the wavelengths shorter than 3,000 tween the two. It is therefore likely angstrom units can be shielded out by that even though each insect might using ordinary glass. The intensity of have an optimum frequency of its own, this type of is given in ergs practical considerations would require per square centimeter. The equipment the use of the optimum frequency for used for biological studies has pro- the material in which it is imbedded. duced relatively low intensity. The. electromagnetic waves can be Ultraviolet rays cause excitation of reflected, refracted, and diffracted. the molecules but not ionization. This The waves can be reflected from any excitation sometimes causes chemical sharply defined gap if its dimensions changes. The absorption of ultraviolet are at least comparable to the wave- rays seems to depend on the molecular length and of a different dielectric structure of the material and on its constant from that of the medium. color. The wavelength of about 2,600 Infrared rays have been used for angstrom units is the maximum ab- heating insects to the death point. If sorption length for one group of acids the insects are in grain or other such often found in biological life. material, the material itself has to be Ultraviolet rays do not penetrate heated to the required temperature. very deeply because of high absorption . The infrared rays are readily absorbed and some reflection. 4i8 Yearbook of Agriculture 1952 G. F. MacLeod, at Cornell Univer- trie charge to produce ionization. The sity, found that bean weevil adults neutron with no charge produces ioni- were not killed when exposed for 20 zation indirectly by giving high veloc- minutes at 30 cm. to a 5-ampere, 100- ity to a nucleus by inelastic collision or volt, 6o-cycle Cooper Hewitt burner, by disrupting a nucleus. When ioniza- but most of the eggs were killed when tion is severe, often other side effects, exposed for 15 minutes. such as secondary X-rays, are pro- J. G. Carlson and A. Hollacnder, at duced. The Geiger-Müller counter is the Oak Ridge National Laboratory, one of the methods for determining found that the mitotic ratio of grass- ionization. hopper neuroblast exposed to ultra- The principal difference in the ef- violet rays of 2,537-angstrom wave- fects of the various types of ionizing length was reduced from 0.97 to 0.58 radiation is in the density of the ion as the intensity was increased from 750 clusters and the depth of penetration. to 24,000 ergs per centimeter. They X-rays and gamma rays produce very also found that the length of exposure low ion densities but penetrate deeply. time was not important as long as the The shorter wavelengths penetrate material received the same total more deeply than the longer wave- amount of radiation. lengths. The atomic particles produce ion densities in relation to their mass SEVERAL FORMS of radiant energy or self-energy and their electric can be projected with enough intensity charge. The alpha particles produce to cause ionization of molecules on much higher ion densities than the which they impinge. X-rays, one of smaller electrons, but the penetration the widely used forms, are usually pro- is greatest with the small particles. duced by impinging high-velocity elec- The penetration would depend on the trons (cathode rays) against platinum intensity of electromagnetic radiation in a vacuum tube. Gamma rays re- or the velocity and electric charge of semble X-rays, but have shorter wave- the atomic particles and on the density length and are usually produced by the of the material on which they impinge. disintegration of radium. Various The greater the penetration the less atomic particles can be projected dense the ion clusters, but the density against materials with extremely high of the ionization would not necessarily velocities and thus cause ionization. be uniform along the path of the ion- The particles include electrons, alpha izing radiatron. In the case of the elec- particles, dcutrons, (which are the trons, the maximum ionization occurs nucleus of "heavy" hydrogen), and at about one-third the depth of pene- neutrons (which can be obtained from tration. When the velocity of the atomic piles ). The atomic particles atomic particles increases sufficiently can be accelerated to high velocity by their mass also increases, which fact such machines as the Betatron and the agrees with the Einstein theory that Cyclotron. These machines use mag- mass and energy are the same thing. nets to rotate the charged particles in The energy unit used in nuclear spiral paths while they are being ac- physics is the electron volt. It is de- celerated by high voltage. The X-rays, fined as equal to the neutrons, and gamma rays cannot be that a particle carrying one electronic bent by magnets. The different forms charge acquires in falling freely of radiant energy produce ionization through a potential drop of one volt. by various methods. The electromag- It is often convenient to use the mil- netic (X- and gamma) rays produce lion-times greater unit: million elec- ionization by Compton or tron volt (mev). the . They are I mev=3.83X io~^* g. cal.= much less efficient than electrons or 1.07X10""^ mass units = alpha particles, which utilize an elec- 1.60 X 10"^ ergs = 4.45 X i o"^^ kw.-hrs. Radiant Energy and Insects 419 Most of the machines used to ac- ities. The inventors say the ultrashort celerate particles or produce X-rays are exposure time of using accelerated classified according to their potential electrons destroys biological organisms in volts. with the minimum amount of harm- The unit used to express the ab- ful side effects to the material. The sorbed energy in is reason is that a time element is re- rep ( roentgen-equivalent physical). quired for a chemical change but not This replaces the roentgen unit (r) for a biological change. which has been widely used in X-ray All kinds of ionizing radiation can work and which is primarily a unit for be used under proper conditions for energy dissipated in an arbi- sterilization and preservation. The trary material, air, where i r is about argument in favor of the electrons is 83 ergs/g. The two are somewhat that X-rays and gamma rays are not similar, but the roentgen unit would usable for practical purposes. The bio- vary for tissue absorption to some ex- logical intensity of penetrating elec- tent with the type of tissue and the trons is about 500,000 to 1,000,000 amount of radiated energy. One rep times greater than that obtainable equals 83 to 100 ergs/g. tissue. with X-rays. The neutron particles A dose of 100,000 rep corresponds that are easily obtained from the to a temperature rise in water of 0.2° atomic pile cause a high amount of C. The temperature effects caused by concentrated ionization that leads to ionizing radiation in the absorber are greater amounts of side reactions than negligible-. would be tolerable. The electrons ac- Many experiments have been con- celerated by tensions up to 10 million ducted on the chemical and biological volts would cause practically no radio- effects of ionizing radiation since 1900, active byproducts in the irradiated and yet the exact nature of what takes products, but the contrary is true of place has yet to be explained. These neutrons. experiments indicate that doses of ra- According to R. D. Evans, a phys- diation required to produce measur- icist at Massachusetts Institute of able chemical changes in vitro often Technology, low-energy electrons, far exceeded those required for pro- when traversing matter, result in found biological changes in vivo. elastic scattering by atomic electrons or According to F. G\ Spear, of the nuclei. The intermediate-energy elec- British Strangeways Research Labo- trons result in ionization by inelastic ratory, ionization and not excitation collision with atomic electrons. The has become generally regarded as the high-energy electrons (above 1.5 mev) link between energy absorption and cause inelastic collision with atomic biological response—there exists in the nuclei and are deflected by the Cou- cell a specially sensitive within lomb field, so that X-radiation, to- which ionizations are biologically ef- gether with ionization, is produced. fective ; any ionization outside the sen- The proportion of radiative and ioni- sitive volume is inefTective. It is known zation losses depends on the type of as the target or "Quantum hit" theory. material. DifTerences in sensitivity to radiation The cathode-ray machine investi- are explained by the chance distribu- gated was of 3-million-volt capacity. tion of ionization in the vital volume The electrons were released from a of the cell. specially designed tube through a One of the methods of producing window device about 15 cm. in diam- ionizing radiation has been investi- eter and of very thin aluminum. gated by the Bureau of Entomology Each discharge of approximately one- and Plant Quarantine. The method millionth of a second was made by uses cathode rays with ultrashort ex- means of a spark gap and the dis- posure time to treat food and commod- charges could be produced about once 420 Yearbook of Agriculture 1952 every second. The air scatters the rays Codling moth larvae buried at var- slightly after they emerge from the ious depths in apples were killed when window so that at a distance of i foot at a depth of 6 mm. with a dosage of from the window the rays cover an 70,000 rep, and when at a depth of area of about i square foot. 8 mm. wdth a dosage of 140,000 rep. The penetrating range of electrons Death of the codling moth larvae ex- depends on the accelerating voltage tended over 16 days at a minimum and the density of the target. Elec- dosage, whereas with an adequate dos- trons of 3 million mev attain a veloc- age the mortality occurred within sev- ity of about 99 percent of light and eral hours of treatment. penetrate into water as far as about Potato tuberworm larvae at depths 15 mm. with the maximum intensity of as much as i cm. in whole potatoes of ionization at a depth of about 4 w^erc exposed to a dosage of 350,000 mm. and tapering on" rapidly below rep. This resulted in 100 percent kill that. of 5-day-old larvae, 95 percent kill Some foods have been treated with of 3-day-old larvae, and 83 percent this machine. The red color in meat kill in 2-day-old larvae. The difference often turned to dark purple when was thought to be due to difíferences in treated at room temperatures^ whereas depth of the larvae in the potato. The in such products as strawberries and 5-day larvae were found at a depth of carrotSj a definite bleaching took place. 4 to 9 mm. wehere the maximum inten- These color changes were eliminated sity of radiation would occur. The w^hen the food was irradiated below younger larvae were less than 4 mm. — 40° C. Tests have indicated that un- from the surface of the potato. desirable side effects could also be eliminated by evacuating the air IN EXPERIMENTAL WORK it is often around the object. Vegetables irradi- necessary to trace the insect or insecti- ated with overdoses of electrons cide. This can be done by using some showed a partial destruction of the radioactive material such as triphenyl- cell walls and oozing-out of the cell phosphate, and taking readings with contents. a Geiger-Müller counter. The counter We exposed some wood samples can be used not only for tracing but containing powder-post beetle larvae also for determining the amount of in- 3 to 7 months old to i and 2 impulses secticide in a particular area. at a distance of 10 inches from the Radiant energy has been experi- window and obtained 100 percent kill. mented with for detecting the presence This dosage was computed to be 145,- of insects in material. When X-rays 000 and 290,000 rep. were projected through material con- Larvae of the confused flour beetle taining insects, the insects could be in an 8-mm. thickness of flour were detected under certain conditions on exposed to one impulse on each side film. and all were killed. The dosage was Reports have indicated that mate- computed to be 310,000 rep. rial exposed to "black light," the Complete mortality of the following shorter ultraviolet wavelengths, may insects resulted from similar treat- cause fluorescence when the light is ment: American cockroach egg cap- projected on insects, thus making it sules, with a dosage of 350,000 rep; possible to detect their presence. yellow-fever mosquito eggs, with a dos- age of 600,000 and 900,000 rep; black MALE SCREW-WORM FLIES have been carpet beetle larvae in 6 mm. of dog sterilized by X-rays and then released food, with a dosage of 310,000 rep; with the hope that if this were done on and bean weevil adults and larvae in a large scale the normal populations one layer of lima beans, with a dosage would be greatly reduced. of 460,000 rep. Many contraptions that supposedly Radiant Energy and Insects 421 use radiant energy for insect control trons or more efficient X-radiation. In have been given wide publicity. Some any case the high initial cost of equip- of them were probably meant to give ment must be considered. satisfactory results^ but the inventor was not familiar with the possibilities THE SUCCESSFUL APPLICATION of of radiant energy. Others probably radiant energy is so dependent on a were meant to fool the public. Some of knowledge of the fundamentals of life these schemes have been investigated. and matter that both must progress One dubious machine was supposed together. The work with insects has to project various insecticides by means opened up possible methods of control, of radio waves. Another machine was however, and with the correlated work supposed to kill insects in fruit by short on mutations has added to the knowl- impulses of high-voltage electric cur- edge of life itself. It is hoped that, with rent. Insufficient time was allowed for the accelerated development of radiant heating and the method did not work, energy equipment in recent years, in- and arcing of the electric charges creased interest will be shown in apply- sometimes damaged the fruit. ing this energy to a study of insect problems. So, IN SUM MARYj the use of radiant energy for controlling insects is still in ALFRED H. YEOMANS, a technologist the experimental stage and will prob- of the Bureau of Entomology and ably remain so for a long time. Plant Quarantine, has been engaged Sound waves do not penetrate most in investigating and developing equip- materials that shield the insect. High- ment used in insect control. Some of frequency waves arc difficult to trans- his studies are concerned with such mit through air, and low-frequency fundamentals as the effect of particle waves do not efficiently produce size, which must he considered when enough heat to kill the insect. High- developing equipment. He is a native intensity waves will shatter the insect of California and a graduate of Ohio and also injure most surrounding State University. materials. Radio waves kill insects by heat and For further reference: also penetrate dielectric materials L. Bergmann: Ultrasonics and Their Scientific and Technical Applications, readily, but the cost of operation com- translated by H. S. Hatfield, John Wiley & pared with other methods, such as Sons, Inc. 1946. vapor heat, makes them impractical to George H. Brown, Cyril N. Hoyler, and use at the present time. Rudolph A. Bierwirth: Theory and Appli- Killing insects by heat produced by cation of Radio-Frequency Heating, D. Van Nostrand Company, Inc. 1947. infrared waves is restricted not only by ]. Gordon Carlson and Alexander Hol- the cost of operation but by the poor laender: Immediate Effects of Low Doses penetrating qualities of this wave- of Ultraviolet Radiation of Wavelength length. 2537 A on Mitosis in the Grasshopper Neu- roblast, Journal of Cellular and Compara- The chemically active ultraviolet tive Physiology, volume 23, No. 3, pages rays have such poor penetrating quali- 157-1^9- ^944- ties that their use for most insect prob- J. H. Lawrence and J. G. Hamilton: lems is impractical. Advances in Biological and Medical Phys- ics, volume I, Academic Press Inc. 1950. The ionizing radiation used so far is G. F. MacLeod: Effects of Ultra Violet cither very inefficient, as with X-rays on the Bean Weevil, Bruchus and gamma rays, or does not penetrate Obtectus Say., Annals of the Entomologi- sufficiently without harming the com- cal Society of America, volume 26, pages modity or material on which the insect 603-615. 1933 F. G. Spear: The Biological Effects of lives. The most promising future ap- Penetrating Radiations, The British Medi- plication of ionizing radiation will be cal Bulletin, volume 4, No. i, pages 2-23 for producing more penetrating clcc- 1946.