Plant Molluscicides
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Journal of Planta Medicinal 1982, Vol. 46, pp. 195—209, © Hippokrates Verlag GmbH - Plant Researchmedica /<'l©© PlantMolluscicides H. Kloos* and F. S. McCullough** * Department of Epidemiology and International Health. University of California, San Francisco, USA. ** Ecology and Control of Vectors, Division of Vector Biology and Control, World Health Organization, Geneva, Switzerland Received: February 5, 1982 Accepted: May10, 1982 Key Word Index: prehensive review on plant molluscicides having yet been published, the purpose of this paper is toas- MolluscicidalPlants; Molluscicide; Snail Control;semble pertinent information and provide general Schistosomiasis; Screening Methods; Target Organ-guidelines and recommendations relevant to further isms; Toxicity Levels. research on plant molluscicides and their role in con- trol programmes. Introduction Review National and international institutions are both Interest in plant molluscicides dates from the currently giving increasing attention to the study of 1930's when ARCHIBALD [12] and WAGNER [1311 advo- plant molluscicides in the hope that they may provecated planting the desert palm, Balanites aegyptiaca cheaper and more readily available than syntheticand B. maughamii ,alongthe water courses of the Su- chemicals.. Many developing countries are reluctantdan and southern Africa, respectively. The laborato- to embark on chemical snail control programmes,ry and field trials of these scientists indicated that the using costly synthetic compounds bought from indus-fruit which fell into the water inhibited the increase of trialized nations with scarce hard currency [28,88]. snail population density. These encouraging findings Recentrigorous legislation governing pesticide devel-prompted the introduction of B. aegyptiaca to Puerto opment und use, has tended to discourage the chem-Rico, where it was planted around a Biomphalaria ical industry from carrying out research even onglabrata infested pool with apparently beneficial re- promising synthetic compounds [137]; not surprising-sults [99]. MOZLFY [86, 87] considered this and two ly, very few candidate molluscicides are presentlyother saponin-containing plants, Sapindus saponaria, available [80]. Whereas synthetic chemicals biode-the berries of which were widely used in Africa and grade slowly, and preliminary evidence suggests thatSouth America as a fish poison and soap, and Swart- some populations of snail hosts may have developedzia madagascariensis, a traditional African medicine resistance to them [7, 80], plant extracts are quite ra-and fish poison [131], to be among the most promis- pidly reduced to simpler substances [57, 88, 89]. So-ing of vegetable molluscicides. Using the berries of me recent studies of plant molluscicides give prelimi-S. saponaria, he controlled a population of Bulinus nary indications that they may be applied effectively(Physopsis) africana in a pond in Zanzibar. In South in different habitats using techniques available in,America, preliminary studies by LUTTERMOSER [731 in and appropriate to, developing countries. Moreover,Venezuela, and by PINTOandALMEIDA [98] in Brazil, the use of indigenous, rather than imported, mate-showed that the berries of S. saponaria were lethal to rials is desirable, especially as strategies for schisto-numerous microscopic organisms, as well as to the somiasis control programmes should be based onhost snails of Schistosoma and Fasciola [129]. Syner- long-term operations. Such strategies should ideallygistic effects were found between extracts of S. sapo- employ a multiplicity of methods (including popula-naria and sodium pentachlorophenate [17, 85]. None tion chemotherapy, focal and seasonal snail host con-of these plants, nor several additional Old World fish trol, environmental and sanitation improvement andpoisons [87, 110, 126], was further exploited for the health education), rather than a singic approach. control of snails. Not until the mid-1960's was the Research on plant molluscicides has become multi-first plant (Phytolacca dodecandra) used for control disciplinary and, as a consequence, the findings haveof schistosomiasis in an endemic focus, in Ethiopia been reported in a wide variety of journals. No com- [62]. 196 Kloos, McCullough Stimulated by these early studies, the search foren plant families, it was noted that the greatest pro- plants with molluscicidal potential was intensified asportion of molluscicidal plants found was in the Sola- exemplified by extensive screening and general im-naceae (8 of 14 plants tested), Phytolaccaceae (both provement of methods and techniques (Table II).species), Fabaceae (3 of 15), Rubiaceae (2 of 12) and AMORINandPESSOA [10]randomlyscreened fresh ma-Euphorbiaceae (2 of 13). All 9 species of the family terial of nine plants indigenous to Alagoas State,Compositae and the 6 grasses were found to be non- Brazil. Three of the plants, Paullinia pinnata, Steno-toxic to snails. These findings reveal certain similari- lobium velutinum and Piptadenia macrocarpa, wereties and contrasts to other studies. Thus, althoughfa- found to be only mildly molluscicidal at 1000 ppm,tropha curcas had no effect on Lyrnnaea sp. in Puerto apparently due to the green state of the plants. SWVARico [82], its roots proved highly molluscicidal against et al. [117] screened another 30 species indigenous toOncomelania quadrasi in the Philippines [142], and Brazil, of which four were toxic to Biomphalaria stra-its seeds moderately so against Bulinus truncatus in minea, but only one, Agonandra brasiliensis, wasSudan [32]. Whereas Randia aculeata and Canna sp. molluscicidal at 100 ppm. Possible confinement ofwere well tolerated by Lymnaea sp., [82], the fruit the active ingredient in the bark, which regeneratesand root of R. nilotica tested by EL-KHEIR and EL- slowly, of A. brasiliensis and Brysonima sericea (otherT0HAMI [32], and Canna indica tested by MAHRAN parts of the plants were not tested) probably pre-et a!. [75], and Adewunmi and Sofowora [5], were cludes their practical use for snail control. The barkmolluscicidal. Paullinia pinnata, well tolerated by of Ziziphus undulata was found to have no effect onlymnaeid snails [82], caused 100 percent mortality in the snails, but BARBOSAandMELLO [18] reported 30 B. glabrata as a 1000 ppm water extract [10], but spe- percent mortality in Biomphalaria glabrata exposedcies of Ipornoea, Urera and Serjania were nontoxic in to a 10 ppm water extract of Z. joazeiro. In northeastboth studies. Similarly, Borreriavercillataand the Brazil several of about one hundred plants studies, two species of Annona tested by MEDINA and WooD- including Pithecellobium multiflorum and Piper tu- BURY [82] and SILvA et a!. [117], showed no mollusci— berculaturn, showed promising molluscicidal activitycidal activity at 1000 ppm. The toxicity of two species [105]. However, fish succumbed at concentrations low-of Phytolacca against Lyrnnaea spp. corroborates the er than those which killed snails [1061, and the resist-findings of several investigators [56]. ance of the plants to physiochemical stress (sunlight, Twenty-three of the 181 methanolic extracts (12.7 temperature, silt and pH) remains to be studied be-percent), representing 106 plant species used in Nige- fore their suitability can be more fully assessed. rian herbal medicine, gave 100 percent kill against MEDINA and W000BURY [82] tested 198 plants indi-Bulinus (P.) globosus [5]. They include the root of genous to Puerto Rico and two to the Dominican Re-Rauvolfia caffra, the stem and root of Bombaxcostat- public. The plants selected for screening were from urn,the fruit of Dialium guineense, the root and stem genera known to have mofluscicidal activity, plantsof Combretum spp., and the root of Terminalia mol- with medicinal or toxic effects in man or domesticus, the root of Cyrpiogonone argentea, the stem of animals, as well as some species randomly selectedAcioa emenii and A. ruatisii, the leaves of Morinda from areas infested with lymnaeid snails. All parts oflucida and Rothrnania whitefleldii, and the leaves of the plant were tested. Thirty species were found to beXiris anceps. lethal to Lyrnnaea cubensis and L. columnella in wa- The suitability of plants having molluscicidal activ- ter extract of 1000 ppm. For further screening theseity only in the roots and stems depends primarily on plant products were oven-dried and tested in watertheir rate of growth, potency and amount of labour extracts at 25, 100, 200 and 1000 ppm. Although He-involved in digging up the roots. Plants endowed with dychiurn coronariurn yielded the most potent extract,regenerative fruiting parts and seeds, being more Solanurn nodiflorum was selected for further study,easily harvested, transported and processed, should due to the uniform distribution of the molluscicidalnormally be given preference. Nevertheless, veg- principle in all parts of the plant [82, 83]. All otheretatively grown tubers may be used advantageously species exhibited great variations in potency, but thein some locales, since they may not require milling or highest toxicity levels were most often found in thestorage and can remain in the ground until used. flowers and leaves. Several species of Solanum areTheir weight and bulk, however, pose problems du- being cultivated for solasodine, a sapogenin used inring digging and transportation, as noted by TEES- the production of pharmaceutical steroids, and at-DALE [126], who field-tested the root of Neorautanenia tempts are being made to cultivate S. mammosum inpseudopachyrhizus in Kenya.