Coca pests and pesticides

Journal of Ethnopharmacology, 1 (1979) 263 - 278 © Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands

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COCA PESTS AND PESTICIDES

TIMOTHY PLOWMAN* and ANDREW T. WElL Botanical Museum of Harvard University, Cambridge, MA 02138 (U.S.A.) (Received February 20, 1979; in final form May 2, 1979)

Summary The major pests of coca are listed and discussed along with methods used to control them in the past and present. Results of analyses for pesticide residues in samples of commercial Peruvian coca leaves are presented. Levels of pesticides found in these samples are too low to be considered a medical risk to coca chewers.

1. Introduction

Coca is one of the most important stimulant and medicinal plants of the New World. Millions of Indians in Peru and Bolivia chew coca leaves every day during work to give themselves energy and to allay hunger. They also use coca for an array of common medical problems. Controversy over the possible benefits and dangers of coca chewing has existed for many years and doubtless will continue. This controversy has obscured the lack of basic research on coca whether anthropological, botanical, sociological, medical, chemical or pharmacological. Many of the most fundamental questions about the plant and its uses remain unanswered. For example, Indian coqueros have long maintained that coca is nutritive and a valuable adjunct to their diets. Non-Indian officials have often ridiculed this claim. But until recently, no nutritional analyses of coca were undertaken. In a recent paper, one of the authors (Plowman) and colleagues discussed the nutritional value of the leaves and reported them to be high in certain vitamins and minerals relative to other items in the diets of Andean peoples (Duke et al., 1975). At that time, the authors cautioned against enthusiasm for coca as a nutritional supplement on two counts: the leaves contain pharmacologically active alkaloids and also may be contaminated with toxic pesticide residues. *Present address: Botany Department, Field Museum of Natural History, Chicago, IL 60605, U.S.A.

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Like many questions about coca, the matter of pesticide residues has never been investigated. In fact, little information is available on the pests and diseases of coca and their management. In the present paper, we shall summarize what is known about the important insect and fungal pests that attack coca and the chemicals used to control them. We shall also present the results of analyses on samples of coca leaves from Peru that we have screened for pesticide residues. Coca leaves are derived from Erythroxylum nouogranatense (Morris) Hieron. and from E. coca Lam. E. nouogranatense is grown on a small scale in the mountains of Colombia by Indian and mestizo farmers. Its variety truxillense (Rusby) E. Machado is cultivated extensively on the north coast of Peru and in the dry, upper Marafion valley. This is the so-called Trujillo coca, much of which is exported to the United States for preparation of decocainized extracts used in the manufacture of Coca-Colaf, By far the most important species, Erythroxylum coca is an important cash crop in the Peruvian and Bolivian Andes. This plant is cultivated principally in the warm, moist, tropical valleys of the eastern Andes, particularly in the departments of Huanuco and Cusco (Peru) and Yungas and Cochabamba (Bolivia). Cultivation of the coca plant and preparation of the leaf for market are still unmechanized, unindustrialized activities, requiring intensive hand labor and employing many people. In some areas, the use of commercial fertilizers and synthetic pesticides have been introduced to increase crop yields. However, most small-scale growers are too poor to afford these products, which are employed primarily by owners of large plantations or fundos. Peru produces over 20000000 kg of coca leaves each year (Daneri, 1974), and this may be a conservative estimate. Production in Bolivia exceeded 12000000 kg in 1974 (South, 1977). Much of this output is consumed by the local population. It is estimated that over half of the working rural population of Peru chews coca daily (Grinspoon and Bakalar, 1976). A significant and increasing percentage of the total production of coca is diverted to the illegal manufacture of crude cocaine paste. The price of coca is rising sharply as a result of growing demands for cocaine on the black market, making coca the most valuable crop in many areas where it grows.

2. The major pests of coca Compared with other tropical American crops, Erythroxylum coca and E. novogranatense are relatively pest-free. Herbivorous insects are only rarely observed on the plants in the field; damage to leaves is often relatively minor. This is especially noteworthy since, during much of the year, the membranaceous leaves of coca are found in the tender state of unfolding, the result of their being stripped 3 to 6 times a year during harvests. The presence of cocaine and other alkaloids in the leaves of the cultivated species is apparently an effective chemical defense against foliovores. In recent

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analyses, dried leaves of E. coca were found to contain an average of 0.76% cocaine; leaves of E. novogranatense contained an average of 0.4 7% (Holmstedt et al., 1977). It should be noted that cocaine accounts for only 70 - 80% of the total alkaloidal fraction of coca leaves. The details of the alkaloid chemistry of Erythroxylum species are still not well known in spite of the distinction of this genus being the sole natural source of cocaine and related compounds. The few studies which have appeared on the pests and diseases of cultivated coca have been conducted in Peru and Bolivia on Erythroxylum coca and E. novogranatense var. truxillense. To our knowledge, nothing has been published on the pathogens of E. novogranatense in Colombia. Some cursory observations have been made on fungal diseases of this species in cultivation in the Old World tropics. Among agronomists, there has been little attention given to the most basic problems of insect predation, fungal diseases and control possibilities, especially during the past 25 years. For these reasons, we shall outline below the major insect and fungal pests of coca which have been reported to date and the methods which have been employed to combat them. (1) Eloria noyesi Schaus (Lepidoptera, Heterocera, Lymantriidae)

Common names: Peru: malunya, malungiii, La mariposa, gusanera, gusano de tela, la tela, sullopuncho (Garcia Calderon, 1924; Wille, 1932a,b et seq .) Bolivia: ulo, ulu (Mortimer, 1901; Alcazar, 1909; Valdivia, 1937; Murillo, 1949) The larva of Eloria novesi is by far the most serious pest of Erythroxylum coca. Eloria is a genus of 61 species according to the most recent monograph on the group (Collenette, 1950). The species are distributed throughout tropical America from southern Mexico to Argentina, essentially the same distribution as neotropical Erythroxylum species. It has been suggested that species of Erythroxylum constitute the principal food plants of Eloria species, but the life cycle of only one species of the moth has been studied (Collenette, 1950). However, Plowman has observed the characteristic larvae and webs of Eloria on the leaves of several wild species of Erythroxylum in the Peruvian Amazon, includingE. macrocnemium Mart., E. macrophyllum Cav. and E. amplum Benth. A thorough study of the biological interrelationships between these two groups of organisms is greatly desired. The life cycle and economic importance of Eloria noyesi has been studied in some depth by Wille in the cocales (coca plantations) of Huanuco (Wille, 1931, 1932a,b, 1937, 1943) and in Cusco (Wille, 1933). This species is also reported from other coca producing regions of Peru (Pozuzo, Oxapampa, La Convencion and Sandia) and Bolivia (Yungas, Cochabamba). The larvae feed exclusively on Erythroxylum coca and pupate on the same plant. Eloria noyesi has not been recorded on E. novogranatense in Colombia or in northern Peru and perhaps does not feed on this species. The adult

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Fig. 1. Plant of Erythroxylum coca showing defoliation of upper branches by Eloria noyesi. Tingo Maria, Huanuco , Peru (Plowman 5843).

moths fly poorly and only during the early morning and late afternoon during daylight. They are typically found resting in fruit or shade trees planted in and around the coca plantations. The larvae develop in about one month and may eat up to 50 coca leaves during their short lives. They also attack the young shoots of the plants which grow out following harvest. Normally, Eloria larvae are very abundant only from December to April. In a bad year, they can destroy up to 80% of the coca harvest. If the larvae devour the terminal shoots following several successive harvests, even strong coca shrubs may be killed, resulting in serious losses to the grower. Various methods of control have been employed to eliminate the larvae of Eloria. One of the oldest and most costly is handpicking, usually done by women and children. Wille (1931, 1932a) recommended dusting the plants with calcium arsenate powder immediately after harvest, and every two weeks thereafter until three weeks before the next harvest. He stated

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Fig . 2 . Eloria noyesf found on Ery throxylum coca, Tingo Marfa, Huanuco , Peru (Plowman 5843). Left : larva; right : adult.

that the heavy rains in the coca growing area would wash away any arsenate residues on the leaves before they were picked. Similarly, Valdivia (1937a,b) suggested lead arsenate powder to combat E . noyesi outbreaks in the Bolivian Yungas. Several natural insecticides were also used formerly in the Yungas region. Alcazar (1909) suggested three plant poisons which reputedly were effective against the ulo : dried leaves of negro quichila (Urticaceae, genus not given) , and the roots of sacha (Lonchocarpus sp .?) or charara (unidentified). Murillo (1949) suggested experimental trials using DDT, pyrethrum or lead arsenate, but there is no indication that these were systematically tested. In the most recent account, Wille (1951) recommended repeated applications of 0.5 % DDT in water. Today modern insecticides are used in Peru to control Eloria. We were told by growers in Tingo Marfa (Huanuco) that both Carbaryl and Dieldrin may be applied to the plants following the harvest. We do not know at present how much of these substances are used or how widespread insecticidal spraying in cocales might be. (2) Leaf cutting ants (Acromyrmex spp ., Atta spp .) Common names: Peru: coqui, cuqui, utaca (Wille, 1932b; Biies, 1935) According to Mortimer (1901) and Wille (1932b), as well as to coca growers in Tinge Marfa, leaf cutting ants can also be a destructive enemy of coca. These ants do considerable damage mainly to seedlings and young shoots. In Huanuco, Wille identified the principal species as Acromyrmex

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hispidus Santschi, although other species are probably involved here as

elsewhere . In Cusco, for example, Biles (1935) mentions three distinct species of coqui, which he referred to the genus Oecodoma (= Atta). In the past, the ubiquitous leaf cutters have been controlled by flooding the nests with water. Usually a stream or irrigation canal is diverted into the nest to drown the subterranean colony. The nests are also fumigated with a mixture of arsenic oxide and burning sulfur or carbon disulfide. In 1951, Wille recommended two toxic compounds to control the coqui : 1% Lindane in powder form to be dusted on the ground and at the opening to the nests; or 5% Chlordane in powder form to be spread on the ground under the plants. In Brazil and in other countries, leaf cutters are now effectively controlled with baits that contain the insecticide Mirex. (3) Eucleodora cocae Busck (Lepidoptera, Heterocera, Oecophoridae)

Common name: Peru: gusano de tela This pest of coca was first reported from the Province of Otuzco on the north coast of Peru near the city of Trujillo in 1928 (Anonymous, 1928; Barton, 1930a,b). It occurs exclusively on Trujillo coca and has not been found in other regions. During the 1930s, there were outbreaks of this pest in several other northern districts where Trujillo coca is grown. Unlike Eloria noyesi, the adults of Eucleodora fly in the evening. The larvae spend all of their lives on the coca plant, feeding on the leaves and young shoots. During the worst months of infestation, from April to August, the larvae may damage up to 90% of the coca harvest. Little is known of the life cycle, geographic distribution or present economic consequences of the depredations of Eucleodora. Barton (1930a,b) and Wille (1932b) recommended dusting the plants with calcium and lead arsenate, respectively, following the harvest. More recently, Wille (1951) and Martin Lynch (1952) suggested repeated sprayings with 0.5% DDT in water. Until about 1976, Parathion was also used to control the larvae . After 1976, farmers switched to a 3% Lindane solution which is currently used to a great extent, usually when the young leaves are flushing out following harvest. Lindane is considered a cheap and effective means of control in spite of its known toxicity (R. Collantes, personal communication, Lima, Peru, 1978). (4) Aegoidus pacificus Tippmann (Coleoptera, Cerambycidae, Trachyderini)

Common name: Peru: la groma Another pest found in the cocales near Trujillo is known as la groma, Although this beetle larva is familiar to coca growers in the area, it has only recently been described scientifically (Tipprnann, 1960). To our knowledge , this is the first report which identifies la groma as Aegoidus paciticus, A specimen (Plowman 5602A) was identified by Dr. M. A. Morine of the Museum Nacional de Rio de Janeiro, where the voucher specimen is deposited.

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Fig. 3. Adult of Aeguidus pacificus in hollowed stem of Erythroxylum nouogranatense var . truxillense, Simbal, La Libertad, Peru (Plowman 5602A).

The adult female of la groma lays her eggs in the fissures of the bark near the base of the Trujillo coca plant. The young larva burrows into the stem and gradually excavates channels as it eats its way through the woody tissues toward the central pith where it pupates. Although this destruction of the stem tissues weakens the plant, it is apparently the infestation by pathogenic fungi which is directly responsible for killing the plant, especially during the cold, humid, winter months . Even large, healthy coca shrubs may succumb to the infestations of La groma. At Simbal near Trujillo, we observed appreciable damage and subsequent loss of mature plants. Little is known of the distribution or amount of damage caused by this insect. Recently, growers have been using a very strong solution (12 %) of Lindane to control this pest (R. Collantes, personal communication, Lima, Peru, 1978). Numerous other insects are reported as minor pests of coca, most of them mentioned in the literature by common names only and lacking scientific identifications. These are mostly of local importance and include sundry Lepidoptera, Coleoptera, grasshoppers, leafhoppers and scale insects. Most of these feed on other plants as well and only attack coca in times of food shortages. Spider mites, known locally as arenilla, are reported from cocales in the Trujillo area and may be a problem in certain years. (5) Fungal diseases

Coca is also attacked by numerous species of pathogenic fungi, especially during the wet season (Biles, 1935). Very few studies have been made

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on the pathology of the plants in the field, and most fungal pathogens on coca are known only from scattered reports. A recent review lists the correct names of all fungal diseases which have been reported for Erythroxylum species (Lentz et al., 1975). Damping off is a fairly common problem in coca, especially in the seedbed and nurseries, and may also affect mature plants. One of these organisms - Mycena citricolor (Berk. and Curt.) Sacco (= Stilbum flavidum Cooke) - causes defoliation in Trujillo and Cusco, where it is known as ojo de galla (Biies, 1935; Martin Lynch, 1952). A rust - Bubakia erythroxylonis Cumm. (= Uredo erythroxyli Graz) - also causes yellowing of leaves and premature defoliation in the cocales of Junin and Cusco (Biies, 1935). In general, fungal diseases are treated by applying Bordeaux mixture to the plants following harvest (Bires, 1935; Martin Lynch, 1952). Another widespread disease of coca, the specific origin of which remains unknown, is witch's broom . It is known in Peru as escoba de bruja or hcupa hcupa and in Bolivia as estalla de la coca. This condition is also found in several wild species of Erythroxylum , including E. deciduum A. St. Hil., E. amazonicum Peyr ., and E. ulei O. E. Schulz. "Witch's broom" is a general term for any abnormality in which the branchlets proliferate in a broom -like appearance. This condition affects many woody plants and may be caused by a number of different organisms including fungi and insects. Cardenas (1948) suggested that the causal pathogen in coca was a virus, transmitted by a small black aphid, but this was never confirmed by further studies. Branches infested with witch's broom are usually removed by pruning. If the infestation is great, the plants may be pollarded at the base or destroyed altogether.

Fig. 4. Old plants of Erythroxylum coca infested with lichens and witch's broom, San Francisco , Ayacucho , Peru (Plowman and Jacobs 4713) .

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Infestation of coca plants with various species of lichens is also considered a serious problem by growers, especially in the more humid regions of the eastern Andes and Amazon basin (Mortimer, 1901). Known collectively as barbasco or la rancha in Peru and lacco in Bolivia, various species in at least nine genera of lichens are involved. These form a dense covering on the trunk and larger branches of the shrubs. Local growers at Tingo Marfa and in the Amazon insist that the accumulation of lichens weakens the plants appreciably and lowers the alkaloid content of the leaves. Lichen infestation may be removed by hand labor or by pollarding the plant. Lead arsenate applied after harvest may also be used to control heavy infestations. Genera and species of lichens which have been collected from infested coca shrubs in different coca growing areas are summarized in Table 1. Various loranthaceous parasites, collectively called matapalo, may also inhabit coca plants and diminish productivity. These are generally removed by pruning. The following species of Loranthaceae have been recorded on the several cultivated cocas: Oryctanthus florulentus (Rich.) Urban (Plowman et al. 6946) on Ery throxylum coca (Plowman et al. 6989) in Amazonian Peru; Oryctanthus alueolatus (HBK.) Kuijt (Plowman and Vaughan 5273) on E. nouogranatense (Plowman and Vaughan 5272) in El Valle, Colombia; and Phthirusa pyrifolia (HBK.) Eichl. (Plowman 5829) on E. coca (Plowman 5831) and E. nouogranatense var. truxillense (cultivated experimentally) (Plowman 5829) in Huanuco, Peru.

3. Experimental part 3.1. Materials

Three samples of dried leaves of commercial coca from Peru were analyzed for pesticide residues according to methods described below. These samples were of recent origin, collected from cocales in the three principal growing regions of Peru. The chemical analyses were carried out by Dr. Donald Young of the Food and Drug Administration Laboratory, Boston, Massachusetts. The first sample (A. T. Weill 00) represents Ervthroxvlum coca from a large [undo near Tingo Maria, Department of Huanuco, In this region, growers use relatively modem methods, including applications of chemical fertilizers and pesticides, as well as wood-heated drying rooms to dry the leaves after harvest. Growers here told us that pesticides are applied immediately after harvest, an interval of two to three months. Huanuco coca is the highest priced coca in Peru, having large leaves of good form and flavor and with a moderately high alkaloid content. The second sample (A. T. Weil 206) is E. coca from a small cocal at 1290 m elevation in the Valley of La Convenci6n, Department of Cusco. This is the largest coca producing area of Peru, and growing is mostly on small plots without modem equipment or artificial dryers. In general, growers of this region cannot afford to use chemical fertilizers or pesticides. How-

Teloschistes flavicans (Sw.) Norm. Pyrine berteriana (Fee) Imsh. Usnea sp. Ramalina sp. Parmelia cristifera Tayl. Chiodecton sanguineum (Sw.) Vain. Usnea sp. Parmelia cristifera TayJ. Parmelia latissima Fee Parmelia subarnoldii des Abbayes Usnea sp.

Coenogonium sp, Graphis sp.

Peru: Huanuco : Chinchao

Peru: Huanueo : Tingo Maria

Peru: Ayacucho: San Francisco

Colombia: Vaupes: Rio Kubiyii

Plowman 6060A

Plowman 5826

Plowman and Jacobs 4713

E. W. Davis 12

*Peruvian specimens were identified by Mr. Dan Plas, Colombian specimens by Dr. Martha Sherwood. Voucher specimens are deposited in the Farlow Herbarium of Harvard University.

Lichen

Locality

Voucher number

Lichens collected on Erythroxylum coca*

TABLE 1 t.;) t.;)

-J

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ever, pesticides are used on other crops here, and there may be considerable environmental contamination as well. The most desirable coca from this region grows on poor soils above 1200 m elevation and is called coca de altura : It has a small, thick leaf which is high in alkaloids. The third sample (A. T. Weil 304) is Erythroxylurn nouogranatense var. truxillense, so-called Trujillo coca, from the north coast of Peru near the city of Trujillo. This is a very arid region, and irrigation must be used for coca production. Chemical fertilizers and pesticides may also be used depending on the size of the cocal and the budget of its owner . Trujillo coca has a papery thin leaf, which is lower in cocaine than E. coca but much valued for its aromatic and medicinal properties. It is rarely seen outside of the region where it is grown. Voucher specimens of the leaves analyzed in this study are deposited in the Economic Herbarium of Oakes Ames, Botanical Museum of Harvard University.

3.2. Experimental methods The methods of extraction and cleanup and chromatographic determination used here are standard procedures of the Food and Drug Administration (U.S.A.) for identifying pesticide residues in food crops. Details of these procedures have been published previously (U.S . Dept. of Health, Education and Welfare, Food and Drug Administration, 1977). Briefly, weighed samples of ground, dried coca leaves were blended with water/acetonitrile, filtered, extracted with petroleum ether, transferred to a Florisil column, and eluted with methylene chloride/hexane and two mixtures of methylene chloride/acetonitrile/hexane. The eluates were concentrated in a Kuderna-Danish concentrator for determination by gas-liquid chromatography.

4. Results and discussion The results of the pesticide analyses are given in Table 2. It is noteworthy that most of the pesticides that show up in these analyses have been out of use in the United States for some time because of their long soil and environmental persistence. The BHCs are a family of five isomers of benzene hexachloride (also known as HCH or hexachlorocyclohexane). Only the gamma isomer is insecticidal; in pure form it is known as Lindane. In a normal mixture of BHC, the gamma isomer accounts for only about 12% of the total, the other four isomers being inert material. Lindane is a nerve poison with an action similar to that of DDT ; it is no longer widely used in the United States because of its toxicity (Ware, 1975). The beta isomer of BHC is suspected of causing liver abnormalities in animals (G. W. Ware, personal communication, Tucson, Arizona, 1977).

trace trace 0.060 0 .250

1.780

0.040

0.100

trace 0 .090

0.010 0 .015 0 .026

Erythroxylum coca ATW 206 , Cusco

0 .122 0 .217 0 .082 trace 0 .040

Erythroxylum coca 2 ATW 100, Huanuco

Samples

Erythroxylum

0.800

0.050 0 .240 ~ 0.420

l

0.015 ~ 0 .034 0 .019 trace trace trace 0.040

nouogranatense var. truxillense ATW 304, Trujillo

1.000 10 .000 3.500 3

1.000 7.000 (total DDT)

0 .100 0 .100 0.000

1 .000 (total BHC)

EPA tolerance levels for lettuce l

Arsenic tolerance level is given for grapes. Environmental Protection Agency Office of Pesticide Programs, Washington, D .C., personal communication, June 3, 1978.

3 Voucher specimens are deposited in the Economic Herbarium of Oakes Ames, Botanical Museum of Harvard University, Cambridge, MA .

~ Environmental Protection Agency (1976).

Q-BHC r-BHC 5 -BHC Aldrin Dieldrin Endrin pp'DDE pp'DDD op'DDT pp 'DDT Parathion Carbaryl Arsenic

Compound

Pesticide residues in ppm in coca leaf samples from Peru

TABLE 2 t,:) ~

~

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In the present analyses, no beta-BHC was detected, an unusual result, since the beta isomer is usually seen if the delta isomer is present (D. Young, personal communication, U.S. Food and Drug Administration Laboratory, 1977). Although the BHCs are not readily metabolized, the levels of them found in these samples of coca are too low to be of concern. As a standard of comparison, a BHC level of 1 ppm is considered tolerable on lettuce in the United States (Environmental Protection Agency, 1976). Aldrin, Dieldrin and Endrin are representative of a group of insecticides known as cyclodienes, which have been used mostly as soil insecticides because of their long soil persistence. This characteristic has led to severe restrictions on their use in the United States. The cyclodienes are also nerve poisons but have different mechanisms of action from BHC or DDT. Aldrin is the parent compound of Dieldrin, and these two chemicals may be considered as a single molecule. The levels of these compounds found in the Peruvian coca samples are not of medical concern. A level of 0.1 ppm of Dieldrin on lettuce is considered tolerable (Envrionmental Protection Agency, 1976). Endrin is much more toxic than Aldrin or Dieldrin with an LD 50 of 3 mg/kg orally compared with an LD 50 of 40 rug/kg for Dieldrin . But a " t race" of Endrin in the sample of Trujillo coca is equivalent to a zero in this analysis (G. W. Ware, personal communication, 1977). DDT and its relatives have been the most widely used insecticides in the world. Although they interfere with nerve conduction in both insects and mammals, they are relatively innocuous to humans. However, their long environmental persistence and tendency to accumulate in food chains makes them ecologically hazardous, and the use of DDT has been banned in the United States since 1973 (Ware, 1975). DDE is an aerobic breakdown product of DDT. DDD (also known as TDE) is an anaerobic breakdown product of DDT, formed by the gut flora of animals . The pattern of residues of these compounds found in the samples of coca suggests background environmental contamination rather than the direct result of spraying the plants. The fact that DDE occurs in about the same amounts as DDT on the leaves makes this interpretation most likely (G. W. Ware, personal communication, 1977). The tolerable limit of DDT on lettuce is 7 ppm, of DDD 1 ppm. Parathion belongs to the class of phenyl organophosphate insecticides. They block nerve transmission by inhibiting cholinesterases and are generally more toxic and less persistent than the organochlorine compounds like DDT and BHC. The most widely used form of parathion has been ethyl parathion, and this is probably the form used in Peru today. Currently, methyl parathion is used in the United States; it has a shorter residual life and lower toxicity to man and domestic animals (Ware, 1975). A level of 1 ppm of parathion is allowed on most food crops in the United States (Environmental Protection Agency, 1976). Carbaryl, marketed under the trade name Sevin, is the most popular of the carbamate insecticides, derivatives of carbamic acid that also inhibit

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cholinesterase. The present analysis is not sensitive to levels of carbaryl much below 5 ppm, so that small amounts (of the order of 1 - 2 ppm) might have gone undetected in the coca samples (D. Young, personal communication, 1977). However, the toxicity of carbaryl is relatively low, with levels of 10 ppm allowed on lettuce, for example (G. W. Ware. personal communication, 1977). Inorganic arsenical insecticides were in wide use in world agriculture until the mid·1950s, when the more complex organic compounds largely replaced them. Both arsenite and arsenate salts have been used , and they owe their toxic action to arsenite and arsenate ions. These ions have several different biological effects. They uncouple oxidative phosphorylation, inhibit enzymes containing sulfhydryl groups, and denature proteins. Arsenical insecticides can cause acute and chronic poisoning in humans. The tolerable limit of arsenic on grapes is 3.5 ppm. The levels found on the coca samples are well below this value.

5. Conclusions The possible presence of pesticide residues on a leaf crop destined for direct human consumption is a matter of concern, whether the crop is a food or a medicine. Andean Indians may chew 30 to 80 g of dried coca leaves daily for most of their lives (Grinspoon and Bakalar, 1976). They retain quids of leaves in the mouth, sucking them dry of juices and flavors, then ejecting the residue. Even so, it may be assumed that a thorough extraction of any pesticide residues takes place. The results of this preliminary screening of coca leaves for pesticide residues do not give cause for alarm. The levels detected are so low that even chewing large amounts of leaves for years would not cause any serious toxicity. We must emphasize that these results are not complete. We were able to test only three samples from scattered locations in Peru . Furthermore, since our analyses were completed, we learned of the great increase in the use of Lindane on Trujillo coca; leaves of this variety should be retested as soon as possible for possible toxic levels of this compound .

Acknowledgements We thank Ing, R. Collantes of Lima, Peru, for sharing with us his broad experience and knowledge of the cultivation of coca. We are grateful to Dr. M. A. Manne for the identification of fa groma, to Dr. M. Sherwood and Mr. D. Plas for determination of the lichens; and to Dr. J. Kuijt and Mr. C. W. Greene for identification of the Loranthaceae. We also thank Mr. L. Gershman of the U .S. Food and Drug Administration Laboratory, Boston, Massachusetts, for authorizing the screening of the coca samples in his laboratory, and Dr . D. Young for conducting the actual analyses in

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that laboratory. We are grateful to Dr. G. W. Ware of the University of Arizona for his help in interpreting the analytical results. We appreciate the useful comments, corrections and suggestions made by the following colleagues who read the manuscript: Drs. M. Blum, G. Lamas, P. Ponce de Leon and L. Rivier. Professor R. E. Schultes kindly provided facilities at the Harvard Botanical Museum for the importation and storage of coca leaves. Research reported in this paper was supported in part through a contract with the U.S. Department of Agriculture (No. 12·14 - 1001 - 230, R. E. Schultes, principal investigator) and by a postdoctoral fellowship (to Plowman) from the Katharine W. Atkins Fund at Harvard University.

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