muscles and even convulsions
US National Dispensary (1926)
II Plants with insecticidal or molluscicidal activity
In tropical climates especially, a number of infective diseases are conveyed by insects or molluscs, and the need for prophylactic action has already been mentioned in the discussion on protozoal and viral diseases. Some nematode infections are also transmitted by animal vectors; thus river blindness (onchocerciasis) is transmitted by the buffalo gnat, Simulium damnosum, and in iilariasis caused by Manzonella ozzardi transmission is done by the midge Culicoides furens (Manson-Bahr, 1952). Insofar as the combating of these animal vectors can be based on the use of plants, they will be dealt with here.
(a) Insecticidal plants
Plant-insect relationships are numerous and often contradictory. Plants can provide a home and food for insects, and can live in partial symbiosis with some insects, for instance ants. Thus in Nigeria the spindle-shaped swellings of the branchlets of Barteria nigritiana Hook. (Passifloraceae) are occupied by stinging ants which defend the plant against larvae, caterpillars, beetles, and in fact, as I have found out to my considerable discomfort, against any living creature approaching the plant. Many plants attract insects, through bright colour and the smell of the flowers, to ensure pollination (Fraenkel, 1959). On the other hand, plants can also trap and 'digest' insects. An example is the insectivorous Drosera.
In insects, basic food requirements seem to be very similar and yet most insects feed preferentially only on a few closely related plant species. Fraenkel (1959) assumes that plant substances which are of secondary importance to the metabolism of the plants, such as glycosides, saponins, tannins, alkaloids and essential oils, may repel most insects or other animals but attract those few that feed on the particular plant species, which may have its particular smell or taste. Tests have shown that isolated active substances (glyco-alkaloids, mustard-oil glycosides, essential oils) even induced feeding when incorporated into neutral media (filter paper or agar jelly) or when applied to leaves commonly not accepted by the insects. Euw and Reichstein (1968) isolated 0.1 mg of aristolochic acid from swallowtail butterflies (the larvae of which feed exclusively on plants of the Aristolochia family). This acid protects the butterflies against vertebrate predators (Oliver-Bever, 1970). Like most insects, mites and microorganisms (bacteria and fungi) appear to be affected by the secondary plant products, and a number of plants have constituents with insecticidal action.
Most of the constituents of insecticidal plants are highly toxic for several cold-blooded animals and often their toxic properties are tested in fish. They are virtually non-poisonous to mammals (including Man) when given orally, but when intravenously injected some can produce respiratory paralysis and death by asphyxia (Heftmann, 1975).
A number of Fabaceae are insecticidal. The best known, which are widely used commercially, belong to the genera Derris and Lonchocarpus, and contain 3-20% of rotenone. Unfortunately, the West African species of Denis* and Lonchocarpus*
appear to have less active components than the American or Indian species, but some other Fabaceae, such asEntada africana*, Mundulea sericea* and Tephrosia vogelii*, which are found in West Africa, are very efficient.
All these insecticidal Fabaceae have roughly the same chemical constituents and their efficiency is often measured in relation to the amount of rotenone present.
Rotenone has an isoflavone nucleus combined with a furan and pyran ring. It is said to belong to the isoflavones (Paris and Moyse, 1967, p. 387), or to the phenyl-propanoid flavonoids (Towers and Wat, 1979). Substances chemically related to rotenone, also found in these Fabaceae, are called rotenoids. Thus, degueline is an isomer with a 2-dehydrobenzopyran nucleus; tephrosine or toxicarol have phenolic hydroxyl groups. Derric acid constitutes the common half of the molecule of rotenone and these rotenoids. The oral lethal toxicity of rotenone is low for mammals: 3 g for the rabbit, 0.6 g for the rat and 0.06 g for the guinea pig. In insects and fish it acts on ingestion or contract and is a potent inhibitor of mitochondrial oxidation (Towers and Wat, 1979); it is active in dilutions down to 1:20000000. At this concentration it can kill goldfish in 2.5 h. As a stomach poison in silkworms, rotenone is 30 times as toxic as lead arsenate. It is 15 times as toxic as nicotine when used as a contact insecticide against bean aphis and is 25 times as toxic as potassium cyanide to goldish (Watt and Breyer-Brandwijk, 1962).
Saponosides have been reported to be present in other Leguminosae with insecticidal properties, such as Dichrostachys glomerata (also molluscicidal against Bulinus globulus), Pentaclethra macrophylla and Tetrapleura tetraptera.
Triterpenoids seem to be responsible for the insecticidal activity of Melia azedarach*, Annona spp*. and Santalum album*. The insecticidal action of Sesamum indicum has been attributed to a lignan (sesamin) and that of Duranta repens cultivated in West Africa, to an alkaloid. Vemonia pauciflora, with sesquiterpene lactones (vernolide and hydroxyvernolide), is considered useful for killing termites.
Larvicidal properties have been found in Thevetia neriifolia (aucubine, flavonic heteroside), Uvaria chamae (chamaenetin, benzylflavanone) and Spilan thus uliginosa (spilanthol). The leaves of Melia azedarach are insect repelling through their meliacins and a repellant action is found in many essential oils. The oils of Ocimum basilicum and O. canum are reputed to repel ants and moths. (For details on U. chamae, O. basilicum and O. canum see Antibacterial plants).
Derris spp. have been introduced in certain parts of West Africa (Congo, the Ivory Coast and Nigeria). They were originally used in China and India and were introduced into the USA and Europe towards 1930 (Paris and Moyse, 1967, Vol. II, p. 388). Commercial Derris is mainly obtained from Southern Asia (D. elliptica Benth. and D. malaccensis Prain). The roots of these contain 4—20% of rotenone. Seasonal variations of the rotenone content have been reported (Nandy and Gupta, 1968). Rotenone is colourless and odourless, and thousands of tons of rotenoids are used against agricultural parasites and to relieve domestic animals of insects. In its commercial formulation, rotenone is often associated with pyrethrins (from certain plants of the genus Chrysanthemum, referred to as Pyrethrum, not present in West Africa), which act more rapidly but are less stable and more expensive to produce (Paris and Moyse, 1967, Vol. II, p. 389). Prenylated flavonoids (derricin, derridin, lonchocarpin, etc.) are almost ubiquitous in Derris and Lonchocarpus spp. and may be considered as biogenetic precursors of the rotenoids (Delia Monache etal., \97%),
Lonchocarpus sericeus Poir. H.B. & K. syn. (Robinia sericea Poir.) FABACEAE
L The bark is employed as a stomachic and laxative and in Nigeria for convulsions and backache. It is applied locally for parasitic skin conditions and eruptions. In America this species has been listed, together with other Lonchocarpus spp. as an insecticide (Dalziel, 1937).
C From the roots, seeds and leaves of this tree, lonchocarpine has been isolated in the Congo (Castagne, 1938). It was identified as a 5-hydroxy-2,2-dimethyl-3-chromen-6-yl-strylycetone. From the leaves, sterols (including /3-sitosterol), prenylated flavonoid precursors, p-coumaric acid, quercitin, rutin and hyperosid have been isolated (Kerharo and Adam, 1974; Delia Monache et al., 1978). The main commercial sources for rotenone are the American L ■ nicou DC. and L. urucu Phillips & Smith. In the Nigerian L. laxiflorus Guill. & Perr., Pelter and Amenechi (1969) reported an isoflavonoid and a pterocarpanoid.
Entada africana Guill. et Perr. syn. (E. ubaguiensis de Wild., E. sudanica Schweinf., Entadopsis sudanica (Schweinf.) Gilb. & Boutique) MIMOSACEAE
L This tree has many local uses. It yields an inferior quality gum and the leaves are used as cattle fodder. The bark of root and stem yields a long fibre used for cordage, commonly for roof-binding, the tying of grass matting, etc. In Northern Nigeria and Northern Ghana, an infusion of the leaves or of the bark is taken as a tonic and stomachic. The leaves also constitute a good wound dressing, preventing suppuration (Dalziel, 1937).
C Rotenone has been reported to be present in the plant (Gaudin and Vacherat, 1938) and saponosides have been found in the bark and leaves (Githens, 1949).
P An infusion of the leaves at a concentration of 1:1000 kills Carassius auratus (goldfish) in 12 h but was not toxic even in doses of 5 g/kg to the guinea pig (Gaudin and Vacherat, 1938).
Mundulea sericea (Willd.) Chev. syn. (M. suberosa (DC.) Benth.) FABACEAE
L The bark is known to be poisonous and both bark and seeds are used as a fish poison in Nigeria, Ghana, India, Sri Lanka, Tanzania and Zimbabwe. It is said to kill and not merely to stupefy. Both bark and roots have been suggested as an insecticide (Dalziel, 1937).
C Worsley (1936) has isolated rotenone, deguelin, tephrosin and some alkaloids and glycosides from the bark. Chopra et al. (1941) confirmed the presence of rotenone. Mundelone or mundulone of isoflavonoid structure has been isolated from the bark as well as a rotenoid, munduserone, and a flavonoid, sericetin (Finch and Ollis,
1960). In addition, the flavanones lupinifolin, lupinofolin, mundulin, mundulinol and a chalcone, sericone, have been reported by van Zyl et al. (1979). The plant is also said to contain hydrocyanic acid (Watt and Breyer-Brandwijk, 1962).
P In India the root, bark, leaves, stem and seeds are all said to be toxic and several authors consider the plant to be an extremely efficient fish poison capable, even, of killing small crocodiles (Chopra et al., 1941). According to Worsley (1937) it is considerably more toxic to insects than Tephrosia vogelli Hook. The bark is said to be equivalent in toxicity to the root of Denis elliptica, despite a lower percentage of rotenone but the toxicity of plants grown under different conditions varies and the smooth bark from the closed forest region is much more toxic than the rough corky bark of the savannah areas. The leaves, root and bark have proved to be efficient against Chrysanthemum aphids (Watt and Breyer-Brandwijk, 1962, p. 636).
Tephrosia vogelli Hook. FABACEAE
L The shrub was formerly cultivated throughout West Africa, and used to stupefy fish (this has been prohibited in Southern Nigeria). If the pounded leaf is thrown into a creek the fish are temporarily paralysed and can be lifted out of the water. Most commonly the leaves are used alone but in some districts people also use them with the ¡rods or use the pod only. A very dilute solution is sufficient to produce paralysis and death in fish.
C Two main constituents, deguelin and tephrosin (hydroxydeguelin) have been found not only in the leaves but also in the roots, fruit capsules and seeds. The leaves also contain a volatile oil, tephrosal, which is responsible for their pungent odour (Hanriot, 1907; Castagne, 1938). Furthermore, rotenone, dehydroxydeguelin, rutin and tetrahydroxy-3,6,7,4'-methoxy-5-flavone (which was called vogeletin) have been reported to be present in T. vogelii (Vleggaar et al., 1978) and rotenoid extraction from the leaves was carried out by Barnes and Freyre (1966a, b, 1967).
P By simple contact, fish kept in a 2% dispersion of the leaves have died within 3 h and those kept in a 1% dispersion in 12 h. On the other hand, guinea pigs ingested as much as 5 g/kg without adverse effects. When injected intravenously, however, a leaf extract corresponding to 0.01 g/kg of tephrosin has killed dogs in 5 min whilst the injection of 0.01 g/kg of pure tephrosin produced death through respiratory arrest only the day after, preceded by accelerated breathing and convulsive effects alternating with paralysis (Hanriot, 1907). Concentrations of tephrosin as low as 1:50000000 paralyse fish and a delayed fatal effect may occur. The Tephrosia rotenoids are also toxic to insects, batrachians, worms and snails. Although deguelin is about half as efficient a piscicide as rotenone (it kills fish in a dilution of 1:20000000 at 27°C in 4.5 h whilst rotenone in the same circumstances kills fish in 2.5 h (Barnes and Freyre, 1966b, 1967)), in Tephrosia it is the leaves which contain the active rotenoids rather than the roots as in Denis and Lonchocarpus spp. After 22 years of storage the dried leaves of Tephrosia were still able to kill goldfish and larvae of worms (Watt and Breyer-Brandwijk, 1962).
Spilanthes uliginosa Sw. syn. (S. acmella Chev, S. oleraceae Jacq.) COMPOSITAE Bresil cress, para cress L The flowerheads of S. uliginosa have a pungent taste and cause salivation. They are chewed in Nigeria and the Cameroons to relieve toothache and are used in local application as a haemostatic and analgesic (Dalziel, 1937). In India, they are also used for sore throats and gums and in paralysis of the tongue (Chopra et al., 1956). C The flower tops of both species contain Spilanthol, which is an unsaturated amide and may be identical with affinine (from Erigeron affinis) (N-isobutyldecatriene-2,6,8-amide), a sterol and a non-reducing sugar (Paris and Moyse, 1971, p. 458). P Extracts of the plants have a depressant action on the guinea pig ileum and on the blood pressure of cats and dogs. In mice the maximum dose tolerated intraperito-neally is 100 mg/kg (Dhar et al., 1968). Spilanthol has been said to have local anaesthetic action (Chopra et al., 1956). It also has a larvicidal action. Extracts of the flowerheads in a soapy suspension and spilanthol kill Anopheles larvae in a dilution of 1:100000 (Kerharo and Adam, 1974) and the whole plant has insecticidal properties towards cockroaches and bedbugs (Heal and Rogers, 1950).
A 50% ethanol extract of the plant is reported to have antibacterial action against Staphylococcus aureus, Salmonella typhi, Escherichia coli, Mycobacterium tuberculosis and Agrobacterium tumefaciens. Antifungal activity was found against Candida albicans, Trichophyton mentagrophytes and Aspergillus niger. Antiviral action was seen in Raniket disease and against Vaccinia virus, and antiprotozoal action against Entamoeba histolytica. Finally, the plant has an anthelmintic effect towards Hymenolepis nana (Dhar et al., 1968).
Melia azedarach L. (Fig. 4.10) MELIACEAE
Persian lilac, bead tree L Cultivated in Nigeria, its bark has been used as an anthelmintic. In India, the country of origin, the juice of the leaves is used internally as an anthelmintic, antilithic, diuretic and emmenagogue (Chopra etal., 1956). The seeds are prescribed for rheumatism and the oil is considered to be similar in its properties to Neem oil. C Schulte et al. (1979) isolated triterpenoids, steroids and aromatic compounds from the air-dried roots. These compounds are 24-methylene-cycloartanone, cylco-eucalenone, 4-stigmastene-3-one-2,4-campestene-3-one, 4-methylene-cyclo-artanol, triaconthanol, cycloeucanol, ß-sitosterol, ß-sitosterol-D-glucoside, vanillic aldehyde, transcumanic aldehyde and vanillic acid (Kraus and Bokel, 1981).
In the fruit and heartwood they found the same cyclonastone derivatives as in the roots, plus two additional substances: 21,23,24,25-diepoxy-tirucall-7-en-2 l-ol and a protolimonoid (Nath, 1954; Schulte et al., 1979). An alkaloid paraisine (ocaziridine) was found in the leaves. In the rootbark of the Nigerian species the limonoids gedunin and 7-deacetoxy-7-oxogedunin, the nimbolins A and B (meliacin cinnamates), meliarrins A and B, as well as the products of decomposition (fraxinel-lose and azedainic acid) were reported, besides 24-methylene-cycloartanone, cyclo-eucalenone and cycloeucalenol (El Said et al., 1968; Ekong et al., 1969b; Okogun et al., 1975). In Israel, the protolimonoids melianon, melianol, melianodiol and meliantiol as well as an apo-eupol derivative were found by La vie et al. (1967) and La vie and Levy (1969) in the roots and bark.
P Aqueous extracts of the fruits have been found to produce dyspnoea, tremor, convulsions and death in rabbits. In cats, dogs and sheep they produced paralysis and narcosis (Murthy and Sirsi, 1957, 1958). However, Ekong etal. (1968) found no components toxic to mice from Indian M. azedarach. The LD50 in mice was 1.04 g/kg for ether and chloroform extracts and 1.5 g/kg for a triterpene mixture.
The insecticidal properties of the leaves, stems and bark have been clearly demonstrated on crickets, cockroaches and Aedes aegypti (Heal and Rogers, 1950) and make Melia a very superior insecticide. It has also been noted that plants sprayed with triterpenoids of the fruit are not visited by insects (Henry, 1949, p. 781; Bezanger-Beauquesne et al., 1981). The repellant substance found in Melia leaves (3.5%) has been named meliatin. It is very similar in its properties to cail-cedrin (Chauvin, 1946). Anthelmintic properties have also been reported for Melia by
Fig. 4.10. Melia azedarach L.
Fig. 4.10. Melia azedarach L.
Chopra et al. (1938) and Cortex azedarach was included in the US Dispensary as an anthelmintic against tapeworm and ascarides, and as an antiparasitic.
The bark is said to act as an antispasmodic and tonic. Some antimicrobial activity of extracts of the leaves, bark and seeds has been reported by Nickel (1959), mainly on Gram-negative bacteria. The extracts were inactive against Paramecia (Spencer et al., 1947a). In anticancer tests the extracts were only slightly active against sarcoma 180 and adenosarcoma 755 (Abbot et al., 1966).
Annona muricata L. ANNONACEAE
Annona reticulata L.
The leaves of these introduced spp. have been reported to have anthelmintic activities in their country of origin (Nadkarni, 1954; Watt and Breyer-Brandwijk, 1962) and an aqueous solution of the seeds of A. reticulata kills most wood bugs (Lecanium). Insecticidal activity has also been reported for the seeds, stems and roots of A. muricata and A. reticulata (Steenis-Kruseman, 1953). A. muricata has a potent insecticidal effect against Macrosiphonella sanbomia. Against Aphis ruminis the toxicity of the roots of A. muricata is inferior to that of Derris elliptica (Heal and Rogers, 1950; Kerharo and Adam, 1974). The insecticidal constituent of the leaves and roots is resistant to heat, but not to saponification, and may be related to fatty acids of high molecular weight (Hegnauer, 1962-68, Vol. Ill, p. 120). Both Annona spp. contain hydrocyanic acid and A. reticulata contains 0.12% of anonaine.
L The people of Northern Nigeria use the leaves of this small tree, mixed with cereal cakes, or in the form of a large bolus mixed with soda and bran, as an anthelmintic for horses. The bark and root have been similarly used. The leaves are also applied as a dressing mixed with the latex oiCalotropisprocera and of Euphorbia balasamifera in the treatment of epizootic lymphaginitis in horses (Dalziel, 1937). C The leaves of A. senegalensis have been found to contain rutin, quercetin and quercitrin (Mackie and Ghatge, 1958) and in the stembark, positive reactions for alkaloids, saponins and tannins have been obtained (Persinos and Quimby, 1967). The leaf contains a hard and a soft wax, both of which contain higher saturated fatty acids. From the hard wax, primary alcohols and palmitone (hentriacontanone), and from the soft wax a yellow sesquiterpenic oil has been obtained (Mackie and Misra, 1956).
P The soft leaf wax has proved to be effective against Sclerostoma larvae from horse faeces; this action has been attributed to the sesquiterpenes. The twigs of A. senegalensis produced 100% mortality oiOncopeltus fasciatus in concentrations of 500 /xg/ml (Jacobson et al., 1975).
Annona squamosa L. ANNONACEAE
Sweet sop, sugar apple
L In Northern America and in Gambia the leaves of the sweet sop are used as an insecticide and to eliminate bed-bugs (Dalziel, 1937). In Indonesia the seeds are used against head-lice (Steenis-Kruseman, 1953).
C From the bark, roots, seeds and stems of A. squamosa aporphine alkaloids (anonaine, roemerine, norcorydine, corydine, norisocorydine and glaucine) have been isolated (Bhakuni et al., 1972).
P Anonaine has been found to possess antimicrobial properties against Staphylococcus aureus, Klebsiella pneumoniae, Mycobacterium smegmatis and Candida albicans at the 100 /ag/ml level (Chen et al., 1974). Corydine is reported to have anticancer activity (Bhakuni et al., 1972). An ether extract of the seeds of A. squamosa has been found to act as a stomach poison in the larvae and eggs of Bombyx mori and to be moderately toxic to Musa nebulo and Triboleum castanum adults. When petroleum ether is added to the extract an insoluble resin is formed and this treatment has been found to increase the toxicity against M. nebulo by a factor of six (Mukerjee and Govind, 1958).
Santalum album L. SANTALACEAE
L A native of India introduced in parts of West Africa (Nigeria and the Ivory Coast), this tree is used in India for its scented heartwood, yielding the fragrant sandalwood oil.
C From the bark a triterpenoid has been identified as urs-12-en-3/3-yl-palmitate (Shankaranarayana et al., 1980). The bark is a waste material after sandalwood oil extraction.
P The benzene extract of the bark has insect growth-inhibiting and antireproductive (chemosterilant) properties. Local application of the triterpenoid in micro-doses to freshly formed pupae of economically harmful forest insects (Atteva fabriciella, Eligma narcissus, Eupterote geminata, etc.) produced morphologically defective adults with crumpled wings and shorter abdomen, suggesting a growth inhibition. It has been observed that feeding a glucose solution containing a minute quantity of the compound to freshly emerged moths prevented them from mating and laying eggs, indicating an antireproductive (chemosterilant) effect (Shankaranarayana et al., 1980). These authors write: 'Such chemosterilant compounds of late, are becoming popular as "third generation pesticides" in controlling forest pests without the bad side effects (like toxicity, environmental pollution etc.) generally possessed by common organic pesticides.'
For a more comprehensive list of plants with insecticidal and molluscicidal action see Table 4.6.
Molluscicidal, Bulinus truncatus,
Hussein Ayoub (1983,1984)
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