INSECTICIDES, INSECT REPELLANTS, AND ATTRACTANTS FROM ARID/SEMIARID-LAND PLANTS Martin Jacobson Biologically Active Natural Products Laboratory U.S. Department of Agriculture, Beltsville, Md. Although arid/semiarid land plants do not pro- duce compounds that are more biologically active Four weeds (Acorus calamus, Artemisia triden- against insects than other plants, they lend them- tata, Heliopsis longipes, and Tagetes minuta) and selves more readily to mass cultivation than plants three cultivated plants (Azadirachta indica, Mam- requiring fertile soil for growth and development. mea americana, and Ocimum basilicum) are poten- Since promising pesticidal plants are too numer- tial candidates for crop development and commer- ous to mention here, only the seven with the most cialization for sources of insect attractants, repel- commercial potential are discussed. The scientific lants, or toxicants. Although all could be commer- name, common name (if known), and family of each cially viable, the neem tree (A. indica) is by far the plant are given, followed by a discussion under the most likely to succeed. Its development in the following headings: description, native range, pres- Southern United States and Central and South ent and potential uses, active compounds, extrac- America is highly recommended. tion, cultivation, and constraints to development. The plant kingdom is a vast storehouse of chem- Acorus calamus L. ical substances manufactured and used by plants as defenses against insects, bacteria, fungi, and Common names: Calamus, sweetflag viruses, The American Indians and native tribes in Family: Araceae Central and South America, Asia, and Africa have Description: A. calamus is a semiaquatic, robust used and, in some places, still use decoctions from perennial that can grow on dry land, is 1.5 to 1.8 many plants as medicines for a wide variety of ail- m (5 to 6 ft) tall, has a horizontal rootstock contain- ments (30). The efficacy of these materials for reliev- ing aromatic cells and iris-like leaves, and grows ing pain and suffering is described by Ayensu (5) at an altitude of 900 to 1,800 m (3,000 to 6,000 ft). in the introduction to his “Plants for Medicinal It is winter-hardy and flowers in early summer. Uses With Special Reference to Arid Zones.” Native range: The American variety grows wild Dioscorides (A.D. 40-90) divided poisons into in various provinces from Florida to Texas, Idaho, three classes: animal, plant, and mineral. He listed Ontario, and Nova Scotia. The Indian variety is in- opium, black and white Hyoscyamus, Mandragora, digenous to the plains of India and Burma, Ceylon, Conium, elaterin, aconite, and the juices of Euphor- and the Celebes Islands. The Japanese variety oc- bia species as plant poisons. He was also aware of curs throughout the country. The European varie- colchicum’s medicinal properties. The Remans ty occurs throughout the continent. used Veratrum album and V. nigrum as medicines, Present and potential uses: The roots have been constituents of “rat and mice powders, ” and insec- used from ancient times in India and Japan for the ticides. From the time of the early Remans to the treatment of a variety of ailments and as an insect 20th century, only three efficient insecticides were repellent and toxicant. The essential oils from the discovered: nicotine, pyrethrum, and hellebore. roots of the Indian and European varieties are ob- The discovery of rotenone and several other plant- tained by steam distillation or solvent extraction of derived insecticides followed in rapid succession. the crushed rhizomes. These oils, reported to be Today, a wide variety of plants has been shown to repellent and toxic to clothes moths, house flies, be effective not only as insect toxicants but also as fleas, several species of mosquitoes, lice, and sev- repellents, feeding deterrents, attractants, inhibi- eral species of stored grain insects, are available tors of growth and development, and sterilants. commercially, When the finely powdered rhizome Useful general references on the subject of plant- is mixed with various grains in a ratio of 1:50 (0.9 derived physiologically active materials for insects kg to 45.5 kg) the grains are free from insect damage are those by Jacobson and Crosby (24), Feeny (11), for a year. The dried rhizomes and leaves, as well Kubo and Nakanishi (31), Finch (12), Jacobson as their water infusions, are effective against crop (20,22), and Smith and Secoy (50). pests such as plant lice and beetle grubs (18,19). The 138 Insecticides, Insect Repellents, and Attractants From Arid/Semiarid-Land Plants ● 139 Indian root oil, which is obtained in 5 to 10 per- the use of calamus oil to certain applications, they cent yield, is much more active than that obtained should not prevent use of the oil for agricultural from the Japanese variety which is obtained in less insect control and possibly for medical purposes. than 1 percent yield. The oil causes sterility in male house flies, and low concentrations hamper the Artemisia tridentata Nutt. maturation of ova and cause complete regression of the ovaries. The Indian oil, and to a lesser ex- Common name: Big sagebrush tent the European oil, is highly attractive to female Family: Asteraceae Mediterranean fruit flies, female melon flies, and Description: A. tridentata is a copiously branched male and female oriental fruit flies (25). The roots perennial which has short rhizomes, is aromatic, are used as an insecticide and vermifuge in China. and grows to a height of 3 m. The inflorescence is Active compounds: The major distilled oil com- generally dense and leafy; the flowers are fertile ponent (80 percent) responsible for the repellency and bloom from July to September. The three- and sterility is ß-asarone, or (Z)-2,4,5-trimethoxypro- toothed leaves are 2.5 cm long. The plant thrives penylbenzene. Another component, asarylaldehyde in light, well-drained, dry, stony soils. (2,4,5-trimethoxybenzaldehyde), also is repellent to Native range: Originally a native of Europe, it is many species of insects. Both compounds are at- the prevailing plant of the Great American Desert, tractive to fruit flies (25). Synthesizing ß-asarone which centers around the Salt Lake of Utah and in- and related compounds by a process that gives an cludes portions of Utah, Colorado, northern Neva- overall yield of 79 percent is cheaper than extract- da, and northern Arizona. It is also found in the ing the oil from calamus. The compounds are ex- desert areas of Washington State, in British Colum- pected to be especially useful as fumigants for pro- bia, and in Baja, Calif. tecting stored grain from insects, as they will per- Present and potential uses: Cattle browse this meate grain-filled storage areas without leaving res- plant on the range. The Indians sometimes use the idues on the grain after the areas are ventilated. The brittle branches for thatch. The seeds are eaten by rice weevil, probably the most damaging insect pest many kinds of birds and mammals, and California of stored grains, is vulnerable to ß-asarone (2). Indians grind the seeds into a meal used for mak- Asarylaldehyde is available commercially. ing a kind of pinole. An extract of the pollen is used Several other compounds obtainable from cala- to treat hay fever. mus oil are acoragermacrone, which is attractive An ethanol extract of the dry branch ends is ex- to female melon flies but is not available synthetical- ceptionally effective in preventing feeding on ly (25); at least eight coumarins which are poten- potato leaves by the Colorado potato beetle, Lep- tially useful in the treatment of tuberculosis (38); tinotarsa decemlineata Say (28). The beetle’s resist- and a host of terpenes which have superior germi- ance to insecticides in potato-growing areas is an cidal properties (49) and are used in perfumery (13). increasingly serious problem in several areas of the Extraction: Raquibuddowla and Haq (43) have world, and this resistance probably will become published the details of a countercurrent pilot plant more widespread. Antifeedants could be important method for extracting the oil from the rhizomes in a multiple system approach (integrated pest man- with petroleum ether, which can be recovered and agement) to control this pest (27). In classical times, reused. Three extractions of 25 kg of ground the leaves and shoots of Artemisia species were rhizomes (1.65 mm particle size) at room tempera- added to stored cereals in granaries to protect them ture yield 2.71 kg of oil, from which the active com- from weevils and other pests, and the water in pounds can be isolated by fractional distillation or which they had been steeped was used to kill or re- column liquid chromatography (25). pel insect larvae, fleas, and locusts. Several species Cultivation: The plant is propagated by division. of ticks are killed rapidly by exposure to the vapors It propagates easily in the spring or autumn and of the powdered plant (19). Various parts of the although it thrives in moist soil, it may be grown plant are used in the United States as a vermifuge, on dry land. Active compounds: Although one of the feed Constraints: ß-asarone has a marked depressant ing deterrent compounds in the branches has effect on the central nervous system of mice, rats, been identified as deacetoxymatricarin, other com- and monkeys. It reduces spontaneous locomotor ac- pounds not yet identified are also responsible for tivity in mice and rats, and in monkeys produces the activity. Deacetoxymatricarin shows good anti- a calming effect lasting 24 hours. The onset of ac- feedant activity at a threshold of 20 micrograms/ tion is more rapid than that of reserpine (9). Al- square centimeter (µg/cm2). An extensive series of though these pharmacological properties may limit sesquiterpene lactones and a number of coumarins 140 .