Plants That

Help Kill Nicotine is the chief insecticidal principle in tobacco. It belongs to the class of compounds known as alkaloids, Insects which are basic, nitrogen-containing plant products having a marked physi- ological action. Other related alkaloids, Ruth L. Bushey notably nornicotine, also may be pres- ent in tobacco. Nicotine derives its name from Nico- tiajia, the genus of plants to which to- In June 1943, DDT was revealed to bacco belongs. The genus was named the American public. Floods of pub- for Jean Nicot, who introduced tobac- licity told of its amazing powers as an co into France in 1560. Chemically, insect killer. Announcements of other nicotine is 1 -methyl-2- ( 3-pyridyl) pyr- synthetic insecticides have followed in rolidine. Most preparations that con- rapid succession. It is not surprising tain it have a strong tobaccolike smell. that many who read those accounts as- Its boiling point is 477° F., yet it evap- sumed that insecticides of natural oi'ates rather rapidly at ordinary room origin, derived from plants, arc out- or outdoor summer temperatures. It is moded and of little importance now- peculiar in that between 140° and adays. The assumption is far from true. 248° F. it is soluble in water in all pro- As each new synthetic ins(x:ticide is portions, but above and below those studied and the ramifications of its temperatures its solubility is limited. It toxicity to man and animals explored, is highly toxic to warm-blooded ani- the problems of removing its residues mals and to most insects, but because of from foods encountered, and its pos- its volatility it disappears rapidly from sible injurious effects on plants exam- products that have been sprayed or ined, we appreciate the value of insecti- dusted with it. Its freezing point has cides, like pyrethrum and rotenone, not been determined, but it is a liquid which are nontoxic to warm-blooded even at -110°F. animals in the small quantities needed Nicotine has been isolated from at for insect control, are safe for plants, least 18 species of Nicotian a and from and leave no harmful residues. a few species in other plant genera. In Within the plant kingdom are many this country it is produced commer- species, known or yet untried, whose cially from Nicoiiana tahacum, the insecticida 1 properties are worth a ordinary tobacco used for smoking and careful search by chemists and ento- chewing. From the woody stems and leaf midribs, which are not suitable for mologists. Today nicotine, pyrethrum, smoking or chewing, we extract the derris, and cube are by far the best nicotine. A coarser species of tobacco, known and most commonly used in- Nicotiana rustica, of higher alkaloid secticides of plant origin, but a few content, is cultivated in Soviet Russia, others are utilized for specific purposes Germany, Kenya, and Hungary as a or in a few localities. Others still in source of nicotine. experimental stages have been found to contain substances highly toxic to THE ALKALOID is obtained by treat- insects. The indications arc that many ing the plant material with an alkali plant insecticides await discovery. solution and distilling by passing steam 765 766 1950-1951 YEARBOOK OF AGRICULTURE through the mixture. The nicotine is Anabasine, a compound isomeric volatilized and carried off by the steam with nicotine (that is, containing the and afterwards condensed by cooling. same proportions of carbon, hydrogen, All parts of the plant contain the alka- and nitrogen), is like it in chemical, loid, but it is chiefly in the leaves. The physical, and insecticidal properties. proportion of nicotine present varies Russian chemists in 1929 isolated from from almost none in high-grade smok- the Asiatic shrub Anabasis aphylla an ing tobacco to as much as 12 percent in alkaloid that they identified as 2-(3- leaves of N. rustica. pyridyl) piperidine and called anaba- Most of the nicotine used as an in- sine because of its source. The year secticide in the United States is sold in before, C. R. Smith, who was synthe- the form of the sulfate, in a water solu- sizing a number of compounds related tion, containing 40 percent of the alka- to nicotine in order to study their toxic- loid. Free nicotine also is available, but ity to insects, found one that appeared it is not so widely used in spraying be- to be equal to nicotine. The compound, cause it evaporates too quickly and be- which he named neonicotine, was iden- cause it is much more toxic to man tical with anabasine. It was unique in than the sulfate. The spray is greatly being first prepared synthetically and diluted for use, as concentrations of later found to occur as a natural plant 0.05 to 0.1 percent of nicotine are constituent. In 1935 Mr. Smith found enough to control most aphids and anabasine in Nicotiana glauca, the wild other soft-bodied insects. tree tobacco native to our Southwest- Many attempts have been made to ern States and Mexico. fix the alkaloid and lengthen its period The Russians have produced anab- of effectiveness. One of the most efiPec- asine sulfate commercially as an in- tive forms is nicotine bentonite, which secticide from Anabasis aphylla, which was developed by a Department of is a salt-loving perennial plant of Agriculture chemist, C. R. Smith, in the family Chenopodiaceae, grow- 1934. It is made by adding nicotine to ing in the semiarid steppes of Trans- a suspension of bentonite (a kind of caucasia, Russian Turkestan, and clay) in water, then drying and grind- neighboring parts of Central Asia. A ing the mixture. The nicotine combines Russian commercial product that was with acidic constituents of the benton- marketed in the United States for a ite and the product, when properly few years before 1934 contained about made, is effective for several weeks 40 percent of anabasine and associated after it is sprayed. It has been used alkaloids. Anabasine has been used ex- especially to control the codling moth tensively in the Soviet Union in the on apple trees. form of insecticidal dusts. Finely ground tobacco, or nicotine The production of anabasine has not sulfate diluted with a carrier, such as been developed commercially in the clay, pyrophyllite, fuller's earth, or talc, United States. Small-scale tests by en- often is used as a dust on vegetable tomologists of the Department of Agri- crops. If a quick-acting dust is desired, culture have shown that it is of the alkaline diluents such as hydrated lime same order of toxicity as nicotine to a are useful. number of species of aphids and other For the fumigation of greenhouses, insects. H. H. Smith, a geneticist in the nicotine is ordinarily used as the free Department of Agriculture, and C. R. alkaloid in concentrated form to be Smith in 1942 studied the alkaloid con- volatilized by heating, or as a mixture tent of several species and interspecific with a combustible organic material hybrids of Nicotiana. They found and an oxidizing agent, like potassium that anabasine was the predominant nitrate, to be applied by burning. alkaloid in N. debneyi, N. glauca, and Further details about nicotine are the hybrid N. tabacum x A^. glauca. given in the chapter that follows. Russian workers have reported as much PLANTS THAT HELP KILL INSECTS 767 as 8 percent of anabasinc in hybrids of dichloridc, and then removing the sol- A^ glauca and A', rustica. De})artraent vent by evaporation to leave a semi- chemists in 1948 began to investigate solid residue, w^hich can b(^ diluted N, ¿llanca as a source of anabasinc for with kerosene or other solvent. insecticidal use and to study methods Many chemists, beginning wath an that might be feasible for extracting Italian named Ragazzini in 1.854, tried the aikaioid on a com.mercial basis. without success to isolate the active Wild plants, collected in Texas, which princi])les of pyrethrum flowers. In contained 1 percent or less of the alka- 1924 two Swiss chemists, H. Staudin- loid were used in the studies. L. Fein- ger and L. Ruzicka, obtained two in- stein and P. J. Hannan developed secticidally active esters, which they methods of extraction that arc satis- called ])yrethrin I and pyrethrin II. factory on a laboratory scale, A plant- A group of De]:>artmcnt chemists, breeding program to develop strains or headed by F. B. LaForge, finally estab- hybrids of N. glauca of higher alkaloid lished the exact chemical structure of content is necessary before develop- the pyrethrins in 1947. They dis- ment as a cultivated croj) can bi^ under- co\'ered that twx:) other very similar in- taken profitably. secticidal esters also are present in jjyrethrum, and they named them EARLY IN THE NINETEENTH CEN- cinerin I and cinerin II. TURY an insecticide jDowder was intro- duced into Europe by an Armenian METHOD^ of making highly purified, trader, who learned its secret while standardized concentrates from pyre- traveling in the Caucasus. The prepa- thrum have been so successful that ration consisted of jDow^dered dried extracts containing 20 percent of pyre- pyrethrum flowers, w^hich had been ob- thrins now arc commercially available. tained from certain species of Chrysan- The extracts are especially useful in themum and probably had been used insecticidal aerosols, w^hich contain the as an insecticide in Persia for a long pyrethrum concentrate and a liquefied- time. The trader's son began to make gas i^ropellent, like Freon-12 (dichlo- it on a commercial scale in 1.828. rodiiluoromethane). Usually the aero- Pyrethrum ])owder w^as introduced into sols also contain one of a number of the United States about .1860. synthetic or natural compounds that Although the pyrethrins, the insecti- greatly enhance the effectiveness of the cidal constituents of pyrethrum, occur pyrethrins w'hen mixed with them. to some extent in several species of the (Most of the aerosols now sold also genus ChrysanthemMm, only C. ciñera- have DDT and an auxiliary solvent as naefolium is used for the commercial ingredients. ) production of insecticides. PyrethrumL in the amount needed as The use of pyrethrum powder grew an insecticide has little toxicity to rapidly. Originally, it w^as employed warm-blooded animals and is not in- m.ainly to control household insects, jurious to plants to which it is applied. because, in the dosages needed to kill It rapidly paralyzes insects, such as insects, it was nontoxic to man and houseflies, and therefore is often used domestic animals. About 1916 kerosene in combination wâth other slower act- extracts of pyrethrum flowers appeared ing insecticides that have a longer on the market and were widely used as residual effect. Because the pyrethrins sprays against flies and mosquitoes. deteriorate rather quickly on exposure Nowadays w^e have highly refined, to light and air, various materials have odorless grades of kerosene for house- been employed as antioxidants to pre- hold sprays. Another and more effi- vent the decomposition, among them cient way of preparing sprays consists hydroquinone and certain substituted of extracting the pyrethrins from the cresols. Better antioxidants for py- flowers wdth a solvent like cthvlenc rethrum arc needed, and Department 002722°—51- -50 768 1950-1951 YEARBOOK OF AGRICULTURE entomologists and chemists are work- all members of the family Leguminosae ing on the problem. and subsequently found to contain a The pyrethrum plant, a herbaceous compound called rotenone. Besides perennial, has flowers that look like our serving as fish poisons, some of the common daisy. The pyrethrin content plants were used locally to control in- is concentrated in the flower heads and sect parasites on humans and animals. increases up to the time the flowers are The Chinese are believed to have fully open. Before the First World War, used "tuba" root, obtained from Der- most of the pyrethrum was produced ris, as an insecticide long ago. In 1848 in Dalmatia, on what is now the Yugo- an Englishman named Thomas Oxlcy slav coast. Shipping difficulties there re- published a report on growing nutmeg sulted in an expansion of production in British Malaya, in which he told in Japan until, in the middle 1920's, about washing with a decoction of Japan had a virtual monopoly of the tuba root the leaves of nutmeg trees trade, although the quality of the Jap- attacked by insects. In 1909 the bot- anese flowers was low. In 1928 experi- anist A. T. Bryant found African Zulus mental pyrethrum culture was under- killing head lice with an extract of taken successfully in Kenya, a British Tephrosia leaves. In 1910 cube {Lon- colony in East Africa. The quality of chocarpus) was used to destroy ticks on the flowers raised there was superior llamas in Peru. In 1911 a British patent to the Japanese, and by 1940 the was issued for the use of tuba root as an United States imported five times more insecticide, but these plant products pyrethrum from Kenya than from Ja- were not commonly employed until pan. The war ended our imports from about 1930. Japan. Limited amounts of pyrethrum Since that time consumption has in- have been imported from the Belgian creased greatly. In 1939 we imported Congo, Tanganyika, and Brazil. In more than 4 million pounds of derris 1945 we imported more than 18 million and cube roots. During the war, im- pounds of pyrethrum flowers. ports of derris were cut ofl", and many Pyrethrum could be grown in the derris plantings in the East Indies were northern United States or in irrigated destroyed or neglected. Our rotenone areas in the West. The hand labor re- imports now consist mostly of cube root quired in harvesting and drying the from South America. flowers has been a deterrent to its cul- A Japanese chemist, Kazuo Nagai, ture here. A mechanical harvester de- isolated a crystalline insecticidal com- veloped by the Bureau of Plant Indus- pound from Derris chinensis in 1902. try, Soils, and Agricultural Engineer- He named it rotenone from the native ing would reduce the cost of harvesting. name of the plant, roh-ten. About 30 The cultivation of pyrethrum has been years passed before the complete chem- attempted in Pennsylvania, Colorado, ical structure of rotenone was learned. and California, but in 1950 there were Then it was determined almost simul- no plantings in this country. taneously by three groups of chemists in the United States, Japan, and Ger- SINCE EARLY TIMES^ natives in many many. The American chemists, who tropical countries, especially the East published their results in 1933, were F. Indies, Africa, South America, and In- B. LaForge, H. L. Haller, and L. E. dia, have used various plants to catch Smith, of the Department of Agricul- fish. As a rule, the plants were crushed ture. They soon devised analytical in water and the mixture was poured methods for rotenone, so that it was into a stream; the fish were stupefied possible to assure the farmer that he and rose to the surface, where they were could buy standardized rotenone dusts collected. Some of the plants so used to treat his crops. were species of Derris, Lonchocarpus, Several other related compounds, Tephrosia, Mundulea, and Millettia, some of them insecticidal, occur along PLANTS THAT HELP KILL INSECTS 769 with rotcnone and arc called rotenoids. Department have shown that the In order to get a good idea of the total rotenone content of this species varies insecticidal value of rotenonc-contain- wddely and is an inherited character- ing roots, usually both the rotenone istic. Since about 1931, breeding exper- content and the total amount of ma- iments have been carried on by Texas terial that can be extracted by a solvent Agricultural and Mechanical College like ether or chloroform are deter- and by the Bureau of Plant Industry, mined. The rotenone content may vary Soils, and Agricultural Engineering to from almost none to as much as 15 develop strains of higher rotenone con- jDcrccnt in rare cases. Market prices are tent for ultimate commercial use. quoted on the basis of 5 percent rote- Strains containing 5 percent rotenone none content. have been obtained. Unfortunately, The original way of using derris as they are not very vigorous. Under the an insecticide, employed by Chinese direction of L. M, Pultz, a horticul- market gardeners in the Malay Penin- turist, experiments are in progress on sula, was 10 beat the fresh root into a cîossing them wdth strains of greater pulp in water and spray the liquid on vigor. Roots of devil's-shoestrings are the plants to be protected. Now derris difficult to grind, and mills of different and cube are used mostly in the form kinds will have to be tried. of dusts made by grinding the dried roots fine and mixing them wdth an MANY OTHER PLANT SPECIES have inert material {like talc, clay, or pyro- been tested against insects. A former phyilite) to give a final rotenone con- Dej^artment entomologist, N. E. Mc- tent of about 1 percent. Dusts also are Indoo, found reports in the literature made by impregnating materials like on nearly 1,200 species of possible in- w^alnut-shell flour or exhausted py- secticidal value. D. E. H. Frear, pro- ri^thrum marc with an extract of the fessor of agricultural chemistry at derris or cube in a volatile solvent, such Pennsylvania State College, has pub- as chloroform, that can be removed lished a list of about 1,450 plant spe- easily by evaporation. Liquid extracts cies wdth which insect tests have of the roots sometimes are made with been made. Several of them appear a water-miscible solvent like acetone, promising. to be diluted wdth water to make a fine For hundreds of years it has been suspension for spraying. For fly sprays, known that the seeds of several species extracts are made with a solvent like of lilies of the genus Schoenocaulon, ethylene dichloride and then diluted commonly known as sabadilla, which with kerosene. grow in Mexico and the United States, In 1947, the late L. W. Brannon, Vvdll kill insects. In 1938 a group of a Department entomologist w'orking w^orkcrs at the University of Wiscon- wdth the Virginia Truck Experiment sin, headed by T. G. Allen, began to Station on methods to control the Mex- study the insecticidal properties of ican bean beetle, discovered that sabadilla. The active substances in the rotenone, like pyrethrum, could be in- seeds are several alkaloids, usually re- creased greatly in effectiveness by mix- ferred to jointly as veratrine. The Wis- ing it with certain synthetic com- consin investigators learned that heat- pounds, especially one called piperonyl ing the seeds or tn^ating them wdth cyclonene. This opened a promising alkali greatly increases the toxicity to field of investigation to chemists and insects. Sabadilla seed can be used as a entomologists. dust mixed wdth a diluent such as lime A Nortifi American plant, Tephrosia or pyrophylfite or as kerosene ex- virgmiana, common as a w^eed in the tract. It loses its toxicity quickly when Eastern and Southern States under the exposed to air and light. It is irritating name of devii's-shoestrings, contains to the mucous membranes and causes rotenone in its roots. Workers in the sneezing if the particles are inhaled. 770 1950-1951 YEARBOOK OF AGRICULTURE In the course of an extensive testing ularly their roots, are toxic to house- program on botanical materials, car- flies. Early in 1950 he isolated from the ried on cooperatively by the New Jer- roots of H. s cabra, which are especially sey Agricultural Experiment Station toxic to houseflies, an amide closely and Merck & Co., Ryania speciosa, a related to the one found earlier in H. tropical shrub native to Trinidad, was longipes, and nam(xl it scabrin. found to have high, specific toxicity In 1948 Jacobson found a very sim- to the European corn borer. A group ilar insecticidal amide in the bark of of Merck chemists in 1948 reported another American plant of a com- that the insecticidal principles in Ry- pletely diflTercnt kind, the southern ania s pecio sa can be extracted with prickly-ash tree Zanthoxylum clava- w^ater or many organic solvents. They hercuUs. had isolated an alkaloid, which they In 1941 a group of Department called ryanodine. Although the active men—Walter T. Swingle, a plant phys- material occurs in gn^atest concentra- iologist, E, H. Siegler, and M. C. tion in the Ryania roots, the stem wood Swingle, entomologists, and H. L. is the source of the commercial insecti- Haller, a chemist — reported the cide, because this part of the plant is promising insecticidal properties of available in larger quantities and also the roots of Tripterygium wilfordii, a because leaving the roots intact per- perennial vine nati\'e to China, which mits further production of the stem has been used in that country for in- wood. The finely ground plant mate- sect control for many years. This plant, rial is used as a dust or suspended in called thunder god vine by the Chi- water as a spray. nese, is related to the American bitter- Workers at the Puerto Rico Agri- sweet. The Bureau of Plant Industry, cultural Experiment Station at May- Soils, and Agricultural Engineering aguez began a study of the insecticidal has made experimental plantings of possibilities of the West Indian tree thunder god vine, first at the Bureau's named Mammea americana, or ma- plant introduction garden at ■ Glenn mey. They have found that the seeds Dale, Md., and later at Knoxville. contain an insecticidal substance, be- Haller and Aeree began in 1939 to lieved to be an ester. The ground seeds investigate the insecticidal constituents or kerosene extracts of them are toxic of the root. They had obtained the to houseflies, mosquitoes, cockroaches, active material in a rather pure state ants, and a number of chewing insects, and had shown it to be an ester alka- like codling moth larvae and southern loid, when their w^ork was interrupted armyworms. by other activities connected with the In 1945, three Department chemists, w^ar. In 1949 the study of the material Fred Aeree, Jr., Martin Jacobson, and was resumed by another chemist in the H. L. Haller, isolated an insecticidal Department, Morton Beroza. After he compound, an amide, from the roots had found that the alkaloidal fraction of a Mexican plant, w'hich they isolated by Haller and Aeree contains thought was Erifueron affinis. (An at least two difl'erent comj^ounds, he amide is a compound derived from an began the work of separating and organic acid and ammonia.) Later the identifying them. plant w^as identified as Hcliopsis lon- Many plant products are not in f^ipes, a member of the family Com- themselves toxic to insects, yet have positae. Roots of the plant have been properties that mak(^ them useful in used in Mexico as an insecticide. Mr. the preparation of insecticides. For Jacobson is now investigating three example, I have already mentioned other species of Heliopsis, which are that certain substances greatly enhance native to the United States, H. scahra, the effectiveness of the pyrethrins H. gracilis, and H. parvifolia. He has against insects. Sesame oil contains a found that all three species, partic- compound called sesamin that does so. PLANTS THAT HELP KILL INSECTS 771 The ability of sesame oil to increase the serves as a diluent ¡n some commer- insect toxicity of pyrcthrum, called by cial insecticides. E. L. Gooden, a ])hys- biologists a synergistic ciTect^ was dis- icist in the Bureau of Entomology and covered by Craig Eagleson, a Depart- Plant Quarantine laboratories at Belts- ment entomologist, in 1941. Our chem- viile, is examining samples of many ists separated the oil into different frac- such materials to see wheth(n^ their tions for testing and soon found that it physical properties are suitable for this was the sesamin that was cflFective. purjoose. Some of the waste products Combinations of sesamin and pyreth- he has examined are: Almond, coco- rins are now much used, especially in nut, filbert, ]3ecan, black walnut, and aerosol bombs. Usually a sesamin con- English walnut shells ; peach and apri- centrate is used that is obtained as a cot pit shells: redwood, fir, and south- by]:)roduct in the purification of sesame ern pine barks; sumac leaves; rice oil for food. hulls; corncob fractions, corn stover; Another compound that is much like il ax shives; hemp hurds; and wheat sesamin in chemical structure and has straw\ The most j^romising of thi^se so a synergistic action with the j^yrcthrins far a])pear to be the nutshells, fir and is asarinin. It occurs in the bark of the pine bark, and the hard com]3oncnt of southern prickly-ash tree, wiiich, as corncob. W^ettable DDT powders con- you already know, also contains an taining them as diluents are being insecticidal substance. Other plant con- tested in the field by entomologists. Tlie stituents have been found .that arc botanical diluents are not so ñnn in synergists for pyrcthrum and are chem- particle size as the mineral diluents or- ically related to sesamin and asarinin. dinarily used, but the size is more uni- A common one is pi]:>erine, in black form. Testing has not yet gone far pe]:>])er. enough to fix definitely their value. Essential oils from some ])lants arc The utilization of plants in insecti- attractive to insects. A well-known cides has three as]3ects that should example is citronclla grass, Cymhopo- int(irest the American farmer. gon 11 ardus3 from which we get geraniol First, ])lant ])roducts can control and eugenol, used as baits in traps for many of the insect pests that attack his Japanese beetles. Some plants contain crops, without leaving persistent poi- substances that repel insects. Nearly sonous residues at haivest time. Such everyone is familiar with the use of oil residues may interfere with marketing of citronclla, also obtained from of produce or with feeding of forage to C. nardiis, to repel mosquitoes, and livestock. Vsdth the storage of woolen goods in Second, several of the insecticidal chests of cedar wood to protect them plants that have been discussed could from clothes moths. b(^ grown in the United States and ofTer Vegetable oils have some value as possibilities as new crops for future insecticides, but are not often used for cultivation. that purpose in the United States be- Third, the use of byproducts as in- cause they are more expensive than the secticide diluents would ofTer a market equally effective petroleum oils. They for materials now discarded as waste. are sometimes included in horticultural sprays, however, because they arc good, RUTH L. BUS BEY is.a chemist in the stickers or adhesivos. Soybean oil is Bureau of Entomology and Plant used in this way in nicotine bentonite Quarantine. After graduating from the sprays. Rosin also has been used as an University of Maryland she joined the adhesive in sprays. Department in 1930 to carry on chemi- Waste materials fromi such plant cal studies on synthetic organic insecti- products as nutshells and bark, when cides at College Park, Md. Later she finely ground, may be useful as diluents was engaged in investigations on for insecticide dusts. Walnut-shell flour fumigants. 772 1950-1951 YEARBOOK OF AGRICULTURE Estimate of the major uses of nicotine in the United States in terms of 40-percent nicotine sulfate equivalent

40-percent Host Insect nicotine sulfate

Pounds Animals (other than poultry) Lice, ticks, internal parasites. 25,000 Apples MP*^\^^ 100,000 [Codhng moth 100,000 Broccoli Aphids 75,000 Cabbage and cauliflower do 85,000 Í do 20,000 Cantaloups jCucumber beetle 10,000 ISquash borer 5,000 Celery Thrips 35,000 Cherries. (Aphids . 10,000 iThrips. 25,000 Citrus Aphids 70,000 Cotton do 50,000 [ do 5,000 Cucumber jCucumber beetle. 7,000 ISquash borer. . . . 3,000 Currants Aphids 5,000 Eggplants do 5,000 Gooseberries do 5,000 Grapes ÍBerry moths 25,000 [Leaf hopper 50, 000 Greenhouse flowers and commercial plants. . . Aphids, thrips, white flies, mealy bugs. 150,000 Greenhouse vegetables do 50,000 Home gardens do 400,000 Hops Hop aphid 70,000 Mushrooms Flies, mites 5,000 Onions Thrips 5,000 Peaches [^"^^'^^ 40,000 [Twig borer 12,000 Pears \^^^' P^y"^ 25,000 [Thrips 40,000 Peas Aphids 100,000 Í do 30,000 Pecans JNut casebearer 5,000 [phylloxera 5,000 Peppers Aphids 5,000 Plums and prunes J 15,000 [Pear thrips 50,000 Potatoes Aphids 10,000 Poultry Mites, lice, internal parasites 150,000 Shade trees, ornamentals, and nursery stock. . Aphids and other sucking insects 50,000 Spinach Aphids 30,000 Strawberries do 5,000 Tomatoes do 10,000 Turnips do 20,000 Walnuts do 80,000 Watermelons. I do 20,000 [Cucumber beetle 10,000