This report provides information of activities carried out in research and extension on the use of natural pesticides with special reference to Botswana, Zambia and Tanzania. A network of people involved in natural pest control is listed for each country. The introduction includes an historical background to the use of plant-derived pesticides. Plants of particular interest such as neem, Azadirachta indica, tephrosia, Tephrosia vogelii, milk bush, Euphorbia tirucalli and basil, Ocimum spp., are described in more detail. The use of ashes in stored products is also mentioned. Recommendations for how to strengthen the work on natural pesticides are given with a time perspective of four years.
The Plant Protection Improvement Programme (PPIP) is a regional programme covering Botswana, Tanzania and Zambia The aim of PPIP is to increase the capacity of the region to solve its plant protection problems with particular emphasis on the needs of small-scale farmers. In spite of the considerable amount of publications from workshops, individual research studies, policy reports and project descriptions which underline the importance of plant derived pesticides in plant protection it has been unclear how much of this information has disseminated to the grass roots level. Within the Coordinating Committee of PPIP the question rose as to what extent people are concerned with natural pesticides in the region, working as researchers, advisors or farmers? How is this implemented in practice? Finally, in what way can PPIP strengthen these activities?
As a first step Torsten Andersson, Department of Crop Science, Swedish University of Agricultural Sciences, initiated a compilation of information on the use of natural pesticides in Africa. This was partly done by advertising in Tanzania Agricultural Research & Training Newsletter (1993, vol. VIII: 1-2) and partly done by writing to many private persons and organizations. More than 20 replies were received from various African countries providing valuable information about traditional practice on natural crop protection, on-going experiments and contacts to other persons and organizations known to be involved in work related to natural pesticides. Together with the contacts established later on during the visit in Botswana, Mozambique, Zambia and Tanzania they give a basis for a network among people interested in this matter (Appendix 1). A literature search was also carried out.
During a three week visit in November - December 1993 Amelie Berger had the possibility to meet and discuss with people about work on plant-derived pesticides in Botswana, Zambia and Tanzania. Contacts were also taken with researchers in Mozambique. The terms of reference were: 1) to establish the state of research and development of pesticides of natural origin, 2) to gather information on to what extent pesticides of natural origin are promoted in extension, and if there is any tutorial material available, 3) identify persons interested in and willing to undertake projects on development and use of pesticides of natural origin which may be funded by PPIP and 4) where appropriate make draft proposals together with national representatives for projects on development and use of pesticides of natural origin. Contacts were made with the following persons:
C. Manthe, Department of Agricultural Research (DAR)
P. Ditshipi, DAR
M. Obopile, Department of Agricultural Research (DAR)
I. Javaid, Entomology, Botswana College of Agriculture
B. Göhl, Farming Systems Programme (FAO/SIDA)
P.O.P. Mosupi, Plant Protection Division
S. Yebuah, Dept of Chemistry, University of Botswana
F. W. Taylor, Veld Products Research
G. Nilsson, SANITAS
Personnel at Thusano Lefatsheng Production and Experimental Unit of Natural Products.
L. Chitekwele, Plant Protection Unit, Chilanga
R. Mulenga, ICIPE Pestnet Project, Chilanga
C.K.M. Kaposhi, National Council for Scientific Research
R. Lesseps, Kasisi Agricultural Training Centre
P. Sohati, Msekera Research Station, Chipata
K. Brown Mandola, District Forestry Extension Office, Kabwe
Tanzania (Mainland and Zanzibar)
A.S.M. Ijani, Tropical Pest Research Institute (TPRI), Arusha, at the moment based at Sokoine University of Agriculture (SUA), Morogoro
J.B. Chogo, vice director, TPRI
W. Mziray, National Herbarium, TPRI
J. Bujulu, E. Minja and co-workers at the Plant Protection Division, TPRI
A.O. Moshi and co-workers at Chemical and Physical Division, TPRI
B. J. Buge and co-workers at Handeni Integrated Agroforestry Project, Handeni
A.F. Lana, SUA, Morogoro
F. Senkondo, SUA
D.M.K. Mushobozy, SUA
M. R. Said, Plant Protection Division, Zanzibar
P. Segeren, DANIDA, Departamento de Sanidade Vegetal, National Institute of Agricultural Research, Maputo
Plants are composed of chemical substances of which some are not directly beneficial for the growth and development of the organism. These secondary compounds have usually been regarded as a part of the plants' defense against plant-feeding insects and other herbivores (Rosenthal and Janzen, 1979). The pesticidal properties of many plants have been known for a long time and natural pesticides based on plant extracts such as rotenone, nicotine and pyrethrum have been commonly used in pest control during the earlier half of this century. However, after the second world war, they lost their importance with the introduction of the synthetic organic chemicals. The organic chemicals were concentrated products with a high knock-down effect on pest organisms. The chemicals could be produced in large quantities relatively cheaply and they rapidly substituted most other pesticides in the 1950s.
As is well known the use of persistent organochlorines like DDT and of the acute toxic organo-phosphorous compounds has led to hazardous effects on environment and human beings. In response, efforts were made to strengthen the integrated pest management approach where chemical control, if at all necessary, should be combined with other methods like crop sanitation, resistant varieties and biological control. In addition, attention was directed towards the development of alternative chemicals. One example is the isolation and identification of pyrethrins from the Pyrethrum plant, Chrysanthemum cinerariifolium, which made it possible to synthesize the pyrethroids. These broad-spectrum insecticides with both reduced persistence and toxicity (in relation to organochlorines and organophosphorous compounds) spread over the world in the seventies.
To the disadvantages of pesticide contamination of the environment and human health risks other aspects can be added. Misuse of non-selective chemicals can wipe out the natural enemies and induce problems with development of resistance. About 450 pest species of insects and mites have now developed resistance to one or more major synthetic pesticides (Georghiou, 1986). The yearly consumption of pesticides in developing countries was estimated at 600 000 tons in 1988 with a drastic increase of 184% during 1980-1984 in Africa alone (WHO, 1990). Because pyrethroids and other newly developed pesticides are expensive many of the harmful but cheaper ones such as DDT are still used today.
The success of the pyrethroids has shown the pest control potential of plant derived substances and has revitalized the interest in plants which contain chemical compounds with pesticidal properties. Jacobson, one of the researchers who identified the pyrethrins, reviewed the literature on insecticides from plants, covering more than 3000 plant species during the period from 1941-1971 (1958; 1975). A more detailed information on chemical structure, isolation and properties of major botanical insecticides such as pyrethroids, rotenoids and tobacco alkaloids are given by Jacobson and Crosby (1971). More recently, Grainge and Ahmed (1988) have compiled a global data base which is divided in three sections: 1. A list of 2400 potential pest-control plant species together with a description of the plant and its pest-control ingredients, the mode of action and the organisms which are controlled. 2. Pests (including nematodes, fungi and bacteria) and plants that control them. 3. Poisonous plants and plants controlling human and animal pests. The handbook also includes "the cream of the crop" - a list of 41 plant species with broad-spectrum pest-control properties which deserve special attention with regard to large scale use in developing countries (see Appendix 2).
The neem tree, Azadirachta indica, is so far the most promising example of plants currently used for pest control. This holy tree in India, from where it originates, now has a global distribution throughout the tropics. It is used for many purposes such as shade tree, poles for construction, medicine, tooth sticks and as a source of insecticide (National Research Council, 1992). Since the early seventies much research has been carried out on the pesticidal properties of the neem tree and the results have been published in proceedings from three international neem conferences (Schmutterer and Ascher, 1981; 1984; 1987) supported by Deutsche Gesellshaft fur Technische Zusammenarbeit (GTZ), who also has produced manuals for pest control of field crops. A summary of how neem products are used as bio-pesticides, the mode of action, effects on pests and natural enemies is also produced by Schmutterer (1990). Although the active ingredients in the neem, such as the azadirachtin, are known, it has not been possible to synthesize these complex compounds. Stable formulations of purified extracts are commercialized (Margosan-O and others) and distributed in several countries. Recently in India, during the runup to the signing of the GATT accords, this product has caused debate about the question of patent and the right for farmers to use homemade products from their own neem trees.
In general, plants with pesticidal properties can be exploited in three ways. Firstly, by using parts of plants whole, in powder or as crude extracts in water or other solvents, secondly, as purified extracts, like rotenone and Margosan-O and finally as a key to synthesize a chemical compound which then could be produced industrially. Today there is considerable interest among biochemists and botanists to screen plants for secondary chemical compounds, which could be used for developing medicals and pesticides, particularly in the tropical rain forests where plant species are numerous but threatened with extinction (Downum et al., 1993). However, it is an expensive and difficult process to isolate and identify the active ingredients and further to produce them in formulations which can be commercialized. Further natural pesticides are not uniform products but rather consist of different active ingredients which often vary in concentration from sample to sample. This makes toxicological tests difficult and costly to run (Latum and Gerrits, 1991). Therefore one can expect that the interest of the chemical industry in developing new bio-pesticides is rather limited.
There is an urgent need to build up reliable food production systems in developing countries, not the least in Africa, where people regularly are faced with harsh environmental constraints of drought and pest outbreaks, a constant lack of agricultural inputs and limited financial means. Under the paradigms of sustainable agriculture and self-reliance, different aid organizations have tried to channel their help to small farmers in the tropics in order to facilitate their use of resources which are locally available and can be cheaply maintained. From this perspective natural crop protection could have an important role to play in the many situations where pests seriously hamper agricultural production. The possibility of making raw extracts from plants grown in the neighborhood where the farmer lives assists in ensuring self sufficiency and gives him/her a cheap alternative to conventional pesticides which often are imported using foreign exchange. Large-scale production of natural pesticides based on crude or purified extracts could also provide an income for people in the countryside.
Efforts have already been made to support the development and use of natural pesticides and many Non-Governmental Organizations (NGO:s) in particular have shown an interest in this field. In a policy document about bio-pesticides in developing countries van Latum and Gerrits (1991) outline prospects and research priorities. This document contributes with a useful background of the exploitation of plant-derived pesticides, highlights possibilities and limitations and gives guidance for future work. With regard to extension a handbook on Natural Crop Protection in the Tropics has been published (Stoll, 1988) and it is now in its third edition and is translated into fifteen languages. This book gives information on several common pesticidal plants and about methods of how to make extracts and apply them to field crops and stored products. It also includes the utilization of ashes in pest control.
The agroecological conditions differ greatly between and within the countries and accordingly, there is a large variation in how the existing cultivation systems are maintained. This will influence the pest profile i.e. which insects, nematodes, fungi, bacteria, viruses and other organisms are common and to what extent they need to be controlled. The limited crop production in Botswana due to the dry climate requires less efforts in pest management than in Tanzania and Zambia where a richer and more diversified cultivation of staple and cash crops is found. However, the needs for pest control varies a lot even within these countries owing to regional differences in environment and agricultural production. Nevertheless there is a regional shared interest to some pest-crop complexes which deserve special attention when looking for possible ways to improve the natural crop protection.
Vegetables are important supplements to staple crops and they are also a resource of income for people living near the towns. Crop rotation and the use of resistant varieties are important methods for reducing pest damage but not always enough in order to control insects. In Botswana caterpillars (American bollworm, Helicoverpa armigera), aphids and spider mites are a common problem. Except for Zanzibar where caterpillars in cabbage are a major problem no detailed information was given for other parts of the region although the importance of pests in vegetables was confirmed. There are two ways how the use of natural pesticides could improve the situation for the small holder (and the consumers). Firstly, plant-derived pesticides can be bartered locally and do not have to be bought with money (often foreign currency) which small-scale farmers are short of. In Botswana the cost for one litre of a common pesticide is 80 $US and no one can afford this. Secondly, there is a widespread misuse of chemical pesticides in vegetables. Pesticides which are left-overs from locusts campaigns, as in Botswana, or used in cash crops like cotton (DDT and organic phosphor compounds are still common) or coffee as in Tanzania are used indiscriminately on vegetables. Many of these pesticides have a medium to high persistency taking a long time to break down. In vegetables the period between chemical application and harvest is usually short. The risk of pesticide contamination in the products which are sold on the market is obvious affecting the health of both producers and consumers. Fears for negative consequences on environment and people were pinpointed in Zanzibar where a huge amount of chemical residuals was discovered in 1985. "This was just too much for this little island" as the Head of Plant Division expressed it and initiated the need for new activities in integrated pest management including training and experimentation on natural pesticides.
Post-harvest losses are often more significant than crop losses which occur in the field. In Africa as much as 20-50% of the grain can be lost in maize and pulses because of infestations from weevils, bruchids and other insects (FAO, 1985). Healthy products and clean storage structures are essential to prevent pest damage but may not be enough, in particular if the storage period is long. Chemicals for fumigation or seed treatment are sometimes available but have become less attractive due to the costs. There is a common tradition among farmers at the subsistence level to use natural products such as ashes instead and these alternatives appear to have increased their importance. An enquiry in Zimbabwe showed that the number of farmers who used natural pesticides in addition to chemicals changed from 20% before 1989 to 80 % after (Giga and Mvumi, pers. comm.). A review of how plants and minerals are used traditionally to protect stored products is produced by Golob and Webley (1980). Maize has usually been stored as cobs which makes it more difficult for weevils, Sitophilus spp. to penetrate the grains. However, this common practice has been challenged by the the larger grain borer, Prostephanus trunctatus, a newly introduced storage pest in Africa, which prefers maize cobs rather than grains.
Agroforestry is today extending to many areas of Africa. Growing annual crops together with perennial trees or shrubs increases the versatility of the cultivation system as a whole and hence spreads the risk for the farmer. Trees are an important resource for fuel and have a beneficial effect on soil conservation. Tree plantations are of special interest in marginal areas where living conditions are hard owing to a combination of poor soils, dry climate and population pressure which have led to degradation of soils and severe shortage of wood for burning. The establishment of tree seedlings may be seriously hampered by termites. Seedlings can be protected through the treatment with insecticides before planting but many farmers cannot afford to buy the products. An improper handling of these chemicals, usually persistent organochlorines, can cause negative effects both on the health of the users and on the environment.
Several colleagues are currently involved in work on natural pesticides in the region but apparently with little contact with each other both within and between countries. Briefly, activities in Botswana, Zambia and Tanzania occur on four different levels (Table 1). 1. Collection of information about traditional use of plants with particular reference to crop protection. 2. Simple on-farm trials or demonstrations which usually do not include replications for statistical analyses. 3. Experimental work in field and laboratory using crude plant extracts. 4. Chemical analyses of active ingredients and bioassays of crude or purified plant extracts. Documentation is so far scarce but some examples are given in the more detailed description below. Extension seems to take place in close contact with farmers who are involved in surveys and on-farm trials.
(1) At the Plant Protection Service (PPS) in Botswana Mr P.O.P. Mosupi has started to build up a small herbarium of plants which farmers have told him are useful. Some of these plants are: Ocimum canum, wild basil, which is used in stored products, Nicotiana glauca, wild tobacco, Lantana camara and Tagetes spp, African marigold, which is planted in mixed cropping with the main crop. On-farm trials are currently carried out based on the methods which are suggested in Natural Crop Protection by Stoll (1988). Farmers are advised to use extracts from Allium sativum, garlic, Capsicum frutescens, chillipepper, Nicotiana spp, tobacco and Melia azedarach, Persian lilac (a relative to the neem tree). Raw extracts are made with water or kerosene, which is easy to find, as a solvent. The trials were started recently and the results will be assessed from the feedback given by the farmers.
(2) In a series of laboratory studies Javaid et al. (in prep.) at the Botswana Agricultural College, have investigated the effects of different plant extracts on the development of bruchids, Callosobruchus maculatus. Cowpea seeds treated with powders from M azedarach (bark and fruit), Eucalyptus (leaves), Croton gratissimus (leaves), Solanum nigrum (fruits), Spirostychus africana (leaves), Ochna pulcra (leaves), cloves, Eugenia caryophyllus (flowers) and black pepper, Piper nigrum (fruits) were better protected than untreated seeds. Powders from ginger, Zingiber officinale (rhizomes), turmeric, Curcuma domestica (rhizomes), chili (fruits) and garlic (bulbs) appearently did not have any significant effects. Ashes from cow dung and the "motswere tree", Combretum imberbe, showed promising results. Further studies are suggested to look at active ingredients, mode of action and toxicity to mammals.
Table 1. Recent or current activities concerning natural pesticides in Botswana, Zambia and Tanzania (Mainland and Zanzibar). Figures between brackets refer to paragraphs in the text.
|Collection of information||Plant Protection Service (PPS), Gaborone (1)||District Forestry Extension Office (DFEO), Kabwe (6)||Handeni Integrated Agroforestry Project (HIAP), Handeni (10)|
|National Council for Scientific Research (NCSR), Chilanga (4)|
|On-farm trials||PPS, Gaborone (1) not specified||DFEO, Kabwe (6) termites Kasisi station, Lusaka (7) aphids on citrus, termites spider mites on eggplant||HIAP, Handeni (10) termites, stemborers Tropical Pest Research Institute (TPRI), Arusha (11) larger grain borer and weevils in stored maize|
|Field and laboratory experiments||Botswana College of Agriculture Gaborone (2) bruchids in stored cowpea||Msekera Research Station, Chipata (8) podborers in cowpea Luapula Regional Research Station, Mansa(9) aphids in cabbage fungus in tomatoes NCSR, Chilanga (4) ticks Mt. Makulu Central Res. Station, Chilanga (5) stemborers in maize||Ministry of Lifestock and Plant Protection, Zanzibar (12) caterpillars in cabbage rice beetles, termites Sokoine University of Agriculture, Morogoro (13) Mexican bean weevil in stored beans TPRI, Arusha (11)|
|Bioassays and chemical analyses||Dept. of Chemistry, University of Botswana, Gaborone (3) armoured crickets||NCSR, Chilanga (11) ticks, toxicity tests|
(3) The armoured cricket, Acanthoplus speiseri, eats the grain of maize, sorghum, millet and legumes, in Botswana sometimes reducing the crop production with 80%. The insect is deterred by the mogodiri plant, Rhus pyroides, and work on the pest-plant interactions was initiated by Dr J. Wollard and is now continued by Dr S. Yebuah and co-workers at the Chemistry Department of the University of Botswana. Bioassays have indicated that the plant has antifeedant properties and some active chemicals have been separated from aqueous extracts. Further studies are needed including field experiments and cooperation with entomologist in order to apply the findings in practical pest control. The group work with other Rhus-species as well.
(4) In 1986 researchers at the Livestock and Pest Research Centre of National Council for Scientific Research (Dr C.K.M. Kaposhi and co-workers) started to collect information about small holders use of indigenous plants and their potential in tick control. Surveys were done in the main agricultural areas. Five plant species of the genera belonging to Neurautanenia, Boscia, Acanthosicyos, Courbonia and Tephrosia were found to have acaricidal properties. Cassia abbreviata, "mutili" and "ombwe" are other promising plants, the latter is still being identified. T. vogelii was chosen as the most promising plant to work with in the search for alternatives to chemical acaricides. Field experiments have shown that treatment with crude leaf extract in water at a concentration of 10% w/v gave good control and protected cattle from tick infestation up to 10 days (Kaposhi, 1992). The Pest Unit has got possibilities to carry out toxicity tests on mammals (mice and rats) and such tests are planned for T. vogelii next year. One man is in charge of the laboratory work preparing extracts in water and organic solvents. There is an interest in extending the work to include plant material which could be useful for crop protection but priorities are given to tick control.
(5) Raw extracts from fresh leaves of T. vogelii at a concentration of 15% (1.5 kg soaked in 10 l of water) reduced infestation of maize stem borers and maize streak virus (spead by vectors of Cicadulina spp.) but significant differences in yield was not achieved. The plant extract did not influence oviposition behaviour of the stem borers and it was concluded that the principle mode of action is an antifeedant and not as a repellant (Dr. Mugoya and Mr. Chinsembu are carrying out this work at Mt. Makulu Central Research Station, Chilanga).
(6) Interviews with farmers in Kabwe District, Zambia, revealed that a number of plants were used in local plant protection against termites and other insects. Pods of T. vogelii, "ububa, are crushed into a fine powder and mixed with water, then sprayed on affected plants. Leaves of L. camara are boiled in water for 30 minutes, then sprayed on the crop. Leaves or fruits from the neem tree are crushed and soaked in water, the solution is sprinkled on the crop. Roots from Euphorbia tirucalli, "lunsonga" are soaked in water for 24 hours, the solution is sprinkled on insects and crop. Pods from Swartzia madagascariensis, "ndale", are crushed and put in water, then sprinkled on the crop. Roots and bark from M azedarach are soaked in water for 24 hours and then sprayed preventively or directly on attacking insects. Plant extracts from T. vogelii and E. tirucalli are used to protect seedlings of Eucalyptus and Gmelina arborea in areas where termites are known to cause problems. There are plans to extend and expand the rather small trials and also include the other plant materials as well.
(7) At the Kasisi Mission Station, Lusaka, several plant species are grown for their potential utility in pest control as well as for other purposes like mulching, fodder, shelter and fuel. Plantations of T. vogelii were initiated in 1990. The leaves from Vogel tephrosia are soaked in water for two hours and then sprayed against aphids in citrus, red spider mites on egg plants and used in termite control with good results. Leaves from Gliricidia sepium, madre, are soaked in water and fermented which probably releases coumarins (Lesseps, pers. comm.) before used as a bait for rats. Cassia siamea is used for mulching and compost. It's termite resistant properties and the fact that cattle don't like to eat the leaves, because of their richness in tannins, suggest that this plant can be worth testing as a bio-pesticide. Young trees of neem and M azedarach were grown for future use in crop protection.
(8) In field experiments at Msekera Regional Research Station, Chipata, Zambia, application of leaf extract from Persian lilac, M. azedarach, on cowpea resulted in good control of pod damaging insects dike the lepidopterous Maruca testulalis and the weevil Piezotrachelius varium). Plant extracts from Agave sp. and T. vogelii did not give the same degree of protection (Sohati and Sithanantham, 1992).
(9) Within Farming System Research/Adaptive Research Planning Team (ARPT), Luapula Regional Research Station, Mansa, natural pesticides are tested against insects in cabbage and diseases in tomatoes. Treatments against insects, mainly aphids and caterpillars, comprise extracts from T. vogelii, "ububa" (fresh solution and solution from leaves soaked over the night), Swartzia madagascariensis, "ndale" (leaves soaked in water for 24 hours), Capsicum sp., chilli (ground fruits soaked in water for 12 hours), Ocimum canum, "Iwena" (chopped leaves soaked in water for 7 days), tobacco (dried leaves? soaked in water for 30 minutes) and a synthetic pesticide. There is some indication that crude extract of O. canum can have a positive affect on the control of aphids but neither of the other treatments (except for the chemical) reduce infestation (Thord Karlsson, pers.comm.). Products against diseases include papaya (leaves), garlic (bulbs), tobacco, cow urine, wood ash and a conventional fungicide and results are being analysed.
(10) Within the Agroforestry Project in Handeni, Tanzania, Mrs K.A. Kajias, B.J. Buge and J. Kabelwa are currently collecting information about plants which can be used in crop protection. This is done together with villagers in the region. A thorough documentation on two of them has been written: the leguminose weed creeper Neurautanenia mitis and Pedilanthus cucullatus of the Euphorbiaceae family. Farmers cut the huge root of the weed creeper into pieces and soak them in water. The extract is then sprayed for protection of maize against stalk borers. P. cucullatus were successfully used to protect young coconut stands against termites before the second world war (and the introduction of synthetic chemicals). The plants which can easily be propagated, are now planted in between seedlings of Eucalyptus and Grevillea robusta. Because the sap of the Euphorbiaceae plants is harmful to the eyes the team has been looking for alternatives and has recently found an evergreen shrub with the local name "mnkangala" (in Zigua/Ngua) or "endipilikwa" (in Masai). When building houses the Masai people use to put leaves into the holes where the poles are placed in order to protect the wood from termites. The shrub is common in the the woodlands and is now propagated in the project area. Promising plant materials for termite control and raw extract from N. mitis against stem borers are tested in the field.
(11) At Tropical Pest Research Institute, Arusha, on-farm trials are carried out on stored products. Larger grain borer (LGB), Prostephanus trunctatus has since its introduction into Tanzania in the mid seventies become an increasingly important pest in stored maize together with the common weevils Sitophilus spp. and moths. LGB is less sensitive to treatment of neem than the weevils (Tierto Niber, 1989; Tierto Niber et al., 1992). Silos with maize are therefore treated with a combination of powder and slurries of neem and pyrethrum. This work is part of a PhD-study by Mr B. Tierto Niber at the University of Helsinki.
In Tanzania extractions and chemical analyses of plant material can be carried out at the Chemical and Physical Division of TPRI, Arusha. Toxicity test on mammals could be run if financial support was made available. Activities on natural products are at the moment very low, partly because the responsible chemist, Mr B. Kaoneka, is doing a PhD on antifeedants at the International Centre of Insect Physiology and Ecology, ICIPE, in Kenya.
(12) In 1990 the Plant Protection Division in Zanzibar started experimental work on neem, A. indica, mainly in cabbage, which was heavily exposed to insects and chemicals. Applications with crushed neem kernels in water have given promising results against caterpillars. Crushed kernels are also used around seedlings and in stored products. Mulching of leaves protects against termites. The increased interest in neem initiated the farmers to charge for the kernels and the research team started to look for alternative plants. In 1992 they began work on E. tirucalli. Leaves and seeds are soaked in water and sprayed on the crop. Extract from this plant seems more effective than the neem products and does also control rice beetles (latin name not given). Extracts from tobacco have shown some, but limited, effect. Leaves from E. tirucalli are spread around houses to protect against army ants. Buds from mangrove trees are crushed and used as an insecticide.
(13) At the Sokoine Agriculture University, Morogoro, entomologists have focused on natural crop protection. Beans treated with different plant material were significantly less infested by the Mexican bean weevil, Zabrotes subfasciatus, than untreated seeds after 90 days. Seed treatments comprised coconut oil, powder of Eucalyptus camaldulensis and neem, ashes and a synthetic pesticide. Of the bio-pesticides neem was the least effective (Busungu and Mushobozy, 1991). Mr D.M.K. Mushobozy is now in Alabama for a short period to study the effect of various natural pesticides against termites.
Mr F. Sekondo, is planning to do experiments on leaf extract from T. vogelii against the maize stalk borer, Busseola fusca, pod borers, M testulalis and pod suckers in cowpea and finally against cassava green spider mite. Other plants of interest are Datura sp. (a common weed), cinnamon, Cinnamomum zeylandicum and clove.
In addition to the examples given above several researchers and extensionists working in other areas have contributed with information about natural plant protection with particular reference to Eastern and Southern Africa. Many different plant species are used traditionally as natural pesticides or/and have been explored experimentally (Table 2). Some plants seem to be more popular or tested more often than others. For instance, experiments on the effect of plant extract from tephrosia occurred in six different places in Zambia. Similarly, species of the family Euphorbiaceae appeared to be commonly used in Tanzania. A brief description of some of these plants are given below.
The neem tree, Azadirachta indica, Persian lilac, Melia azedarach, and Trichilia emetica do all belong to the mahagony family Meliaceae. Neem is widely distributed throughout tropical Africa in both dry and humid areas (FAO, 1988). It is grown in many West African countries such as Nigeria, Sierra Leone, Ghana, in plantations in Sudan and Ethiopia and in East and Southern Africa with a predominance in the Swahili dominated areas along the coast.
Table 2. Plants used in pest control either experimentally (E) or traditionally (T) according to correspondents in Botswa, Zimbabwe, Mozambique, Zambia, Tanza (Mainland and Zanzibar), Kenya, Uganda, Ethiopia and Ghana.
|Acanthosicyos sp. T||T|
|Azadirachta indica, neem||E||T||ET||T||E|
|Capsicum frutescens, chilli||T||E||T||T|
|Euphorbia tirucalli, milkbush||T||ET|
|Jatropha curcas physic nut||E|
|Melia azedarach, Persian lilac||E||E||ET||E|
|Solanum nigrum, black pepper|
There is an immense documentation on the neem tree, including the pesticidal properties of neem products (Jacobson, 1989; Schmutterer, 1990; National Research Council, 1992; Saxena, 1993). In spite of this there seems to be a rather limited documentation in Africa of how it should be exploited in practical crop protection with regard to methods of application, dosages and target pests. The most common method seems to be to let dried and crushed kernels soak in water and spray the solution on the crop. This is also the way neem is used in Zanzibar and Kenya (Said and Jro, pers. comm).
For storage protection neem is usually used as a powder from crushed seeds which is mixed with the grain at various concentrations. This gives protection of many insect pests including weevils, Sitophilus spp., khapra beetles, Trogoderma granarium and lesser grain borer, Rhizopertha dominica (Golob and Webley, 1980; Saxena et al., 1989) however, contradictory results are also obtained. The neem product gives a bitter smell and taste which can reduce its attractiveness as a protectant in food grain in particular in areas where there is shortage of water for washing the treated produce (Tierto Niber, pers. comm.). The risk for aflatoxin contamination in the grain owing to neem fruits which have not been dried properly should also be considered (Latum and Gerrits, 1991).
Neem leaves contain much less of the major active ingredient, azadirachtin, than seed kernels and are appearently not used as commonly. Nevertheless leaf powder mixed with beans at a concentration of 5% was shown to be effective against Mexican bean weevils (Busungu and Mushobozy, 1991). Further, water extract from fresh leaves gave a good control of stem borers in maize, Chilo partellus, when applied into the plant whorls in Mozambique (Segeren, 1993).
The azadirachtin content in seed kernels varies with the geographical location of the neem plants with high concentrations found in plant extracts from Nicaragua, Indonesia and Togo and low concentrations in kernels from trees grown in Sudan and Niger (Ermel et al., 1987). The azadirachtin content has also been analysed in relation to development and growing conditions of the trees (Gruber, 1991). Plant extracts from different ecotypes give rise to a variation in the antifeedant activity (Singh, 1987). The relationships between the active ingredient, antifeedant activity and climatic factors are not straight forward but high temperature and relative humidity and exposure to light decrease the content of azadirachtin in the seeds. The fact that the concentration of the active compounds may vary largely between different plant material is probably one reason for the sometimes ambivalent results reported from the field.
Within an GTZ/SIDA supported project in Nicaragua it has been possible to establish tree plantations and a small factory for producing crude neem products which then are commercialized. Regular contacts are taken with the farmers to encourage them to plant their own neem trees and to use neem extracts in pest control. The practical experience from this project could be useful if similar projects are going to be developed elsewhere. The project has published manuals for plantation procedure, technique for processing the plant extract and application methods against various pests (Gruber and Mendes, 1992; Gruber and Miranda, 1993).
The Persian Lilac or chinaberry appears to be a common alternative to neem and there is occasionally a confusion of which of the two plants has actually been used. During a neem planting programme in Ethiopia it was revealed that the seeds used were from the Persian Lilac and not from the neem. There is hence a risk that the two species can be mixed up with consequences for the interpretation of experimental results. Stoll (1988) suggested to use powder of dried leaves and seeds in stored grain. In addition, bark has been used as powder against bruchid bean weevils (Javaid, in prep.) or soaked in water for spraying against termites (Mandola, pers. comm.). Leaf extract in water was not as effective as neem leaves against the stem borers in maize (Segeren, 1993).
A third species of the Meliaceae family, Trichilia emetica, is reported to be used in Mozambique. Treatment with crushed seeds mixed with cowpea at a dosage of 1% gave a 98% protection of the grain and no weight loss after 90 days (Segeren, 1993).
The legume Vogel tephrosia, T. vogelii, is an shrubby plant indigenous to Africa but distributed to many other parts in the tropics where it is used as shelter, cover crop, fish poison and as a pesticide. It was introduced to the United States in the sixties for the purpose of commercial production of rotenone and regarded as a more promising plant than Derris and Lonchocarpus spp which were the main sources of the pesticide (Barnes and Freyre, 1966). In Eastern and Southern Africa T. vogelii and other related species have been grown in small plantations by small holders for their use in crop protection (Watt and Breyer-Brandwijk, 1962). The principle active ingredient is rotenone but there are also other rotenoids such as tephrosin and deguelin which are toxic to fish and mammals. The insecticidal effects have been shown on several different insect species (Grainge and Ahmed, 1988). In bioassays, extracts of these compounds had stronger antifeedant effect on army worms, Spodoptera exempta, sugar borer, Eldana saccharina and pod borers M. testulalis than extracts of azadirachtin (Hassanali and Lwande, 1989).
The most common application method is to soak fresh and crushed leaves in water at a concentration of 10% and then spray the liquid on the crop. Farmers in Malawi use Tephrosia as a dip to protect cattle from ticks and as a fish poison (CIMMYT, 1991). Similar practices are reported from Zambia (Kaposhi, 1992). On the other hand, farmers in the Mansa region are not satisfied with the plant used as a botanical pesticide in crop protection (Thord Karlsson, pers. comm.). Powder of Tephrosia leaves can also be used to protect stored products. In Congo powder mixed with groundnuts at a ratio of 1:40 gave a 98.8% mortality of the Groundnut Borer, Caryedon serratus, after 13 days (Delobel and Malonga, 1987).
There are varietal differences in rotenone concentration in the leaves (Irvine and Freyre, 1959). Changes in latitude and spacing within rows influence the leaf stem ratio and hence the yield of rotenone in plantations (Barnes et al., 1967).
The milk bush, Euphorbia tirucalli is a succulent shrub or tree of several meters height which occur in grassland and savanna woodland thoughout tropical Africa including Madagascar as well as in the Arabian peninsula, India and the Far East (Polhill, 1988). It is easy to propagate with branch cuttings and is often planted in hedges around villages in Eastern Africa. Stem, branches and buds have insecticidal and repellant properties against aphids, grasshoppers and mosquitos (Grainge and Ashmed, 1988). The plant is also used as a fish poison. The plant sap, latex, can be applied as a seed dressing against the plant parasitic nematodes Tylenchorhynchus brassicae and Rotylenchus reniformis to protect vegetables (Siddiqui and Alam, 1988a; 1988b). Leaves, seeds and roots are soaked in water and the solution is sprayed to protect vegetables from caterpillars and seedlings from termites (Said and Mandola, pers. comm.). Because the latex is harmful to the eyes and causes irritation of the skin the plant material must be handled carefully when preparing the crude extracts.
Finger euphorbia is planted near coconut trees to prevent attack by Rhinocerous beetle, Oryctes spp. in Kenya (Onyango Jro, pers. comm.) and similar practice occurred with another Euphorbiaceae Pedilanthus cucullatus in the coastal region of Tanzania before the second world war. The plant is now used in Handeni to protect tree seedlings from termites (von Ramdohr, pers. comm.).
Sweet basil, O. basilicum (syn. americanum) was reported by Irvine (1955) for its potential as a pesticide. Leaves and seeds are rich in essential oils which are repellent, toxic or growth inhibitory to many insects (Grainge and Ahmed, 1988). In field and laboratory experiments treatments with seed extracts against bugs in turnip, Bagrada cruciferarum, the American bollworm, Helicoverpa armigera and aphids, Aphis gossypii increased mortality between 50-90% (Pandey and Verma 1982; Pandey et al., 1983a; 1983b).
There are other wild Ocimum species such as O. suave and O. canum which have been used traditionally against pests. Branches of O. suave are often placed around windows and doors to keep the mosquitos away. Chemical analyses of the essential oils from the plant revealed that the principle compound was eugenol which was shown to have a strong repellent effect on mosquitos (Chogo and Crank, 1981). Linalool is another terpenoid found in hoary basil, O. canum. This chemical compound is responsible for the toxic effect of dried leaves to the bruchid Zabrotes subfasciatus and other storage pests (Weaver et al., 1991). Extracts from O. suave have shown promising results in bioassays on maize weevils, Sitophilus zeamais, carried out at ICIPE, Kenya. The plant was going to be in focus for future evaluation of botanical pesticides in stored grain at the village level (Hassanali and Lwande, 1989). Eugenol and other isolates of essential oils have also a strong inhibitory effect on the growth of many fungi (Garg and Siddiqui, 1992).
To treat the stored grain with ash is a common method of protection against insect pest (Golob and Webley, 1980). The ash is either mixed thoroughly with the grain or added to the stored product in various layers. In Zimbabwe ashes from unnamed sources and ashes from maize cores and Mopane tree, Colophospermum mopane, are predominant in Mashonaland Provinces. Ashes from cattle and goat droppings and from the lead wood, Combretum imberbe, are preferred in Matabeleland Provinces (Giga and Mvumi, pers. comm.). Lead wood is very heavy and burns down to an almost floury ash. It is also used by people in Botswana and was shown to be fairly effective against bruchids in cowpea (Javaid, forthcoming). Wood ash, as well as sand, tobacco dust and dolomite, provided a good protection of maize stored for six months in Malawi (Golob, 1984).
The protective mechanisms of ash is unclear. Desiccation and suffocation are two possible ways of how insects are affected. There may be a variation in how effective different ash products are owing to differences in texture and chemical composition. Although the choice of ash products is likely to be dependent on what is available for the people in a particular area, it could be of interest to carry out comparative experiments of several ash products against the most common storage pests.
Ashes are usually used in stored grain but can also be applied to field crops. Stoll (1988) gives several recipes for protection of vegetables against insects and diseases. In Kenya ash is applied against stem borers in maize (Jro, pers.comm.). In Uganda farmers use ash to protect against sweet potato clear wing, Synanthedon dasysceles, aphids, banana weevils and blight in tomatoes. However, on-farm trials have shown that although ash reduced the infestations its effectiveness in protecting the crop was limited (Brehony, pers. comm).
It is beyond the scope of this study to give a complete coverage of people and activities with connection to natural crop protection in the region. In spite of this limitiation, the overall picture, judged from the several examples given above, shows that there is a widespread interest among researchers and agriculture extensionists to incorporate natural pesticides into the integrated pest management. A shortcoming seems to be that most of the work is carried out on a scattered ad-hoc basis, with little background information and few horizontal and vertical links to other people who study the same plants somewhere else.
It is unclear to what extent the initiatives have been taken within programmes already defined and supported by NGO:s and governmental organizations (at least German, Dutch and Finnish organizations seem to be involved) or because there have been a need expressed by the small holders at the grass roots level. A combination of both is of course also possible.
The constrained economy of many small-scale farmers together with the problems of health risks and environmental pollution owing to chemical pesticides provide strong arguments for carrying out studies on plants with pesticidal properties. These studies can of course be of interest in themselves because they may contribute to scientific knowledge in general making it easier to predict the outcome of different interactions between plants and pests.
However, if the aim is to improve the natural crop protection there must also be an awareness of and response to the experience of the farmers. Current knowledge and new findings about promising plant products need to be transformed into practical applications which are accepted by the users. Neglecting this can lead to a negative feed back from the farmers which results in a decreasing interest to use natural pesticides. This was experienced in the Phillippines where extensive surveys and experimental work on natural pesticides have been carried out for many years (Stoll, pers. comm.).
A crude extract may be effective in bioassays and field experiments where insects are given a choice between treated and untreated plants. In the farmers field there is no choice and unless there are other alternative host plants from the wild flora the insects may overcome their reluctance to feed on the treated plants. Even if a natural pesticide has shown to be effective in the farmers field, extraction and application methods may be so time consuming and labour requiring that the farmers are put off from using the product.
There are no absolute rules of how to carry out investigations on natural plant protection in a fruitful way but interest and dedication are certainly important at all levels. The approach to a problem is dependant on personal and material resources. Although these may vary considerably, some general suggestions are given below for how to strengthen the current work with natural pesticides with the ultimate goal of helping the small-scale farmers.
Collection of information: Information about plants with pesticidal properties can be collected in two ways, either from surveys on the grass root level or from existing databases and current knowledge about the flora in the country.
Surveys can be an important mean for getting to know about traditional plant protection methods and has already given results. Within the Handeni Agroforestry Project the research team uses to walk through the bush together with both young and old villagers, the latter would then point out useful plants which the younger people could learn about. To more directly ask a farmer about plant protection methods may not be the best way to get the right information. Many farmers have been too involved in the use of chemical pesticides and see these as the only method to protect the crop. Although traditional methods are used they are not brought up as a source for plant protection.
There are databases which supply information about potential plants. One example already mentioned is Grainge and Ahmed Handbook of Plants with Pest-Control Properties (1988). A database has also been developed in Zimbabwe (Elwell, pers. comm.) which could provide a valuable source for the region. This database is the basis for a forthcoming joint publication by PPIP and Natural Farming Network in Zimbabwe (Elwell and Maas: Natural pest et disease control). A bibliographic database dealing with storage pests has recently been published by Natural Resources Institute (Rees et al., 1993). A global Natural Product Database, Napralert, is continuously produced by College of Pharmacy, University of Illinois, Michigan, United States and is said to cover all published material on plants with pesticidal properties (Quinn, pers. comm.). Linking the information obtained from the database to the knowledge of the indigenous flora could draw rings on the most promising plants which deserve further studies. Important aspects to consider are not only pesticidal properties of the plants but also their distribution, abundance and easiness to be propagated. Cooperation with botanists at the National Herbaria and Universities would facilitate the work. Help is also needed with the identification of plants used traditionally but only known by their local names. Concentration to some important plants: There is a need to concentrate the work on certain plants in order to cover them as well as possible at different levels. A systematic approach is required. This includes documentation of the botanical aspects (also taking into account the growing conditions), research in laboratory and field, assessment of feed-back from the farmers in combination with improvement of application methods and finally - if the arguments are good enough - production of extension material.
Some plants seem to have attracted researchers and extension officers more than others. They have been described above and deserve special attention. Research on plants with pesticidal properties must of course not be restricted to those species mentioned above. The important point is that whatever plant is chosen a holistic view is desirable.
The versatile use of neem and the fact that the tree can be planted in dry areas make this plant promising. A regional project on how to use neem as a source for pesticides, medicines and contraceptives is now being started at ICIPE with FINNIDA as the principle donor (Takala, pers. comm.). The project will include some research on improvement of neem products, neem tree-crop interactions and evaluation of germplasm. However, main efforts will be directed to extension and the project will include production of information material as well as training courses on how to propagate, prepare and use neem products. A tree plantation has already been established at ICIPE. Future work on neem carried out elsewhere should only be approved by PPIP if it is a well justified complement to the neem project at ICIPE.
Most studies of natural pesticides are concerned with the effects on insects. Plants or crude extracts can also be used against many other organisms (Grainge and Ahmed, 1988) and some examples on the nematicidal and fungicidal effects of E. tiraculli and Ocimum spp were given above. Marigold plants, Tagetes spp., are known for their nematicidal properties and field experiments in Tanzania have shown that intercropping tomatoes with marigold significantly reduced number of root-galls and increased the yield (Ijani and Mmbaga, 1988). Similar results are reported from Kenya (Oduor-Owino, 1993). In laboratory experiments in Botswana, extract from the stem of Dichapetalum cymosum completely inhibited the mycelium growth of the rot pathogen Macrophomina phasealina and fungicidal effects were also found in extracts from M. azaderach (seed and bark), Solanum nigrum (berries) and Pavetta harborri (stem)(Poswal et al., 1992).
Comparative studies with emphasis on the mechanisms: In several studies comparisons have been made between extracts from different plants and their effect on a particular organism (Busungu and Mushobozy, 1991; Sohati and Sithanantham, 1992; Poswal et al.; 1992; Javaid, in prep.). The reason for choosing these plants is often that they have been used locally for medical treatment, in tick control, as fish poison etc. Sometimes a more detailed description is given about the active ingredients which are likely to be involved. A common limitation is that the results are seldom discussed in relation to the mechanisms which are thought to be responsible. The mechanisms behind an extract's pesticidal properties are of course not always understood. Nor are they easy to observe in the field. Bioassays with crude or purified extracts could contribute information about insect behaviour and development and thus facilitate an interpretation of the results. Anti-feedant activity assay with leaf disks in a choice situation has been used at ICIPE and is described by Kubo (1993), other examples of bioassays on fecundity and development are given from the neem tree (Schmutterer and Ascher, 1987).
The target pest of most studies is one single species. However, crops are often hosts for several insects and in the case of vegetables there is a wide range of aphids, bugs, caterpillars and beetles which feed on the plants. It would be useful to carry out comparative studies testing one or a few promising plant materials against various insects with different feeding behaviour.
Regional network, key-persons and work procedure: An overall impression is that many researchers and extension officers work in isolation from each other, independent of the geographical distance in between them. The description of the various on-going activities on plant derived substances which is given in this study, should be seen as a first attempt to create a network of people interested in natural pesticides. Such a network could provide possibilities for developing a mutual exchange of ideas and experiences, concentration on relevant research topics and an avoidance of unnecessary duplication of experiments.
It is important to have interested key-persons who can coordinate the work. Initially they shall be responsible for collection and documentation of available information. This compilation will give a basis for how to concentrate the work to certain plants. The next step will be to formulate projects which are relevant in relation to the ultimate goal of how to improve the use of these plants as natural pesticides. Chemical identification of the active ingredients might be necessary and the question of toxicity to mammals and beneficial insects requires attention. Another aspect to consider is the selection of important crops and target pests. A reasonable time period for compiling information and formulating project proposals is one year. A group of researchers and extension officers could work together on one or a few plants so that different aspects are covered. Each group should be coordinated by a key-person who also will have an advisory role during the experimental period. It is desirable that, whenever it is possible, the same methods are used in order to facilitate comparisons of results from studies carried out at different locations. Scientific support, if necessary, should be provided by PPIP in cooperation with the Swedish University of Agricultural Sciences or other institutions.
Workshop and documentation: A workshop can be a useful tool for strengthening the network. It can provide a forum for discussing how our knowledge about plant-derived pesticides can be transferred into practical applications in natural crop protection which can help the small-scale farmers. The scientific documentation is important and it is recommended that a workshop is held at the end of a two years experimental period. The workshop shall also include a critical analyses of the practical implications, i.e. the feed back from farmers and how extraction and application methods can be improved. The workshop could be replicated at the village level where farmers will be taught how to prepare and use plant material available in their respective areas.
There is a need for extension material and efforts should be made to produce this after the workshop during a fourth year. However, ideas of what kind of information is needed can be discussed already in the beginning. A system of leaflets one for each plant, may give enough flexibility to work with several products at the same time in spite of heterogeneity in the scientific and practical knowledge of the plants. In addition, leaflets can be easily renewed in the light of new findings.
There is a common interest in natural crop protection among many researchers and agricultural extensionists in several African countries. On-going activities in Botswana, Zambia and Tanzania provide examples of investigations on natural pesticides at different levels, from surveys and simple on-farm trials at the village level to field experiments and bioassays in the laboratory. Some plants are more frequently occurring in the studies than others, such as neem and neem related plants, tephrosia and species of the Euphorbiaceae family. There is a lack of a systematic approach to the problems related with the utilization of plant-derived pesticides. Many studies are carried out in isolation with little back-ground information about the plants and what has been done elsewhere. The documentation is so far scarce.
The possibility for small-scale farmers to buy agricultural inputs is limited. This together with the problems of health risks and environmental pollution, owing to misuse of chemicals, provide good arguments for carrying out studies on natural pesticides. Support to these activities is therefore strongly recommended with particular reference to pest problems in vegetables, stored products and tree plantations. The aim should be to develop reliable pest control methods which are attractive and safe for farmers to use. With a time perspective of four years the following recommendations are given:
T. Andersson initiated contacts with many persons and organizations involved in natural pesticides. L. Chitekwele, A.S.M. Ijani, A.F. Lana and C. Manthe gave helpful assistance during field travels. J. Mörner contributed useful information, B. Tierto Niber commented on an earlier draft and P. Sinclair helped with editing. Finally, the contributions from all persons who responded in writing and talking are gratefully acknowledged.
Barnes, D.K. and Freyre, R.H. 1966. Recovery of natural insecticide from Tephrosia vogelii. I. Efficiency of rotenoid extraction from fresh and ovendried leaves. Economic Botany, 20: 279-284.
Barnes, D.K., Freyre, R.H., Higgins, J.J. and Martin, J.A. 1967. Rotenoid content and growth characteristics of Tephrosia vogelii as affected by latitude and within-row spacing. Crop Science, 7: 93-95.
Busungu, D.G. and Mushobozy, D.M.K. 1991. The efficacy of various protectants against Zabrotes subfasciatus (Boh) Coleoptera, Bruchidae in common beans. Bean Research, 6: 62-67.
Chogo, J.B. and Crank, G. 1981. Chemical composition and biological activity of the Tanzanian plant Ocimum suave. J. of Natural Products, 44: 308-311.
Cimmyt, 1991. Farming Systems Bulletin, Eastern and Southern Africa, no. 9.
Delobel, A. and Malonga, P. 1987. Insecticidal properties of six plant materials against Caryedon serratus (Ol.)(Coleoptera:Bruchidae). J. Stored Product Research, 23:173-176.
Downum, K.R., Romeo, J.T. and Stafford, H.A. (eds.). 1993. Phytochemical potential of tropical plants. Recent advances in phytochemistry, vol.27. Plenum Press, New York.
Ermel, K., Pahlich, E. and Schmutterer, H. 1987. Azadirachtin content of neem kernels from different geographical locations, and its dependence on temperature, relative humidity, and light. In Schmutterer and Ascher (eds.) Natural pesticides from the neem tree and other tropical plants, pp. 171-184. GTZ, Eschborn, Germany.
FAO. 1985. Handling and storage of food grains. Food and Agriculture Organization of the United Nations, Rome.
FAO. 1988. Traditional food plants. Food and Agriculture Organization of the United Nations, Rome.
Garg, S.C. and Siddiqui, N. 1992. Antifungal activity of some essential oils isolates. Pharmazie, 47: 467-468.
Georghiou, G.P. 1986. The magnitude of the resistance problem. In Pesticide resistance, strategies and tactics for management. National Aacademy Press, Washington, D.C. pp. 11-44.
Golob, P. 1984. Improvements in maize storage for the smallholder farmer. Tropical Stored Products Information, no. 50:14-19.
Golob, P. and Webley, D.J. 1980. The use of plants and minerals as traditional protectants of stored products. Tropical Products Institute G 138. Now Post harvest pest and quality section, Natural Resources Institute, Chatham, United Kingdom.
Grainge, M. and Ahmed, S. 1988. Handbook of plants with pest-control properties. Resource systems institute, East-West center, Honolulu, Hawaii. John Wiley & Sons, New York.
Gruber, A.K. 1991. Wachstum, Fruchtertrag und Azadirachtingehalt der Samen von Azadirachta indica A. Juss auf verschiedenden Standorten in Nicaragua. PhD-thesis, Technische Universität, Berlin, Germany.
Gruber, A.K. and Mendez, M. (eds.). 1992. Arbol Nim en Nicaragua. Cultivo y aprovechamiento como fuente de insecticidas botánicas. Proyecto Insecticida Botánico NIM, Impreso en Editorial Evangélica, CIEETS, Managua, Nicaragua.
Gruber, A.K. and Miranda, F. (eds.). 1993. Memoria del primer taller de intercambio de experiencias y conocimientos sobre el cultivo del arbol nim en America Latina. 2-6 Novembre, Managua, Nicaragua.
Hassanali, A. and Lwande, W. 1989. Antipest secondary metabolites from African plants. In Arnason, J.T., Philogene, B.J.R. and Morand, P. (eds.) Insecticides of Plant Origin. ACS symposium series 387, pp. 78-96. American Chemical Society, Washington, D.C.
Ijani, A.S.M. and Mmbaga, M.T. 1988. Studies on the control of root knot nematodes (Meloidogyne species) on tomatoes in Tanzania using marigold plants (Tagetes species), ethylene dibromide and aldicarb. Tropical Pest Management, 34:147-149.
Irvine, F.R. 1955. West African insecticides, Colon. Pl. Anim. Prod. 5: 34-38.
Irvine, J.E. and Freyre, R.H. 1959. Varietal differences in the rotenoid content of Tephrosia vogelii. Agron. J. 51: 664-665.
Jacobson, M. 1958. Insecticides from plants: a review of the literature, 1941 - 1953. USDA Agricultural Handbook no. 154.
- 1975. Insecticides from plants: a review of the literature, 1953-1971. USDA Agricultural Handbook no. 461.
- 1989 (ed). The Neem tree. Focus on phytochemical pesticides vol.1. CRS Press, Boca Raton, Florida.
Jacobson, M. and Crosby, D.G. (eds). 1971. Naturally occurring insecticides. Dekker Inc., New York.
Kapushi, C.K.M. 1992. The role of natural products in integrated tick management in Africa. Insect Sci. Applic. Vol. 13: 595-598.
Kubo, I. 1993. Insect control agents from tropical plants. In Downum, K.R. et al. (eds.) Phytochemical potential of tropical plants. Recent advances in phytochemistry, vol. 9. Plenum Press, New York.
Latum, E.B.J. van and Gerrits, R. 1991. Bio-pesticides in developing countries. Prospects and research priorities. ACTS Press, African Centre for Technology Studies, Nairobi, Kenya and ACTS Biopolicy Institute, Maastricht, The Netherlands.
National Research Council. 1992. Neem - a tree for solving global problems. National Academy Press, Washington.
Oduor-Owino, P. 1993. Effects of aldicarb, Datura stramonium, Datura metel and Tagetes minuta on the pathogenicity of root-knot nematodes in Kenya. Crop protection, 12(4): 315-317.
Pandey, U.K. and Verma, G.S. 1982. Effectiveness of some indigenous plant products against insect-pests of cruciferous vegetables, Bagrada cruciferarum Kirk. Z.ang. Ent. 69 (2): 129-132.
Pandey, U.K., Srivastava, A., Lekha, C. and Singh, A. 1983a. Efficacy of certain plant extracts against brinjal aphid Aphis gossypii Glover. Indian J. of Entomology, 45: 313-314.
Pandey, U.K., Srivastava, A., Singh, A. and Panday, M. 1983b. Evaluation of some plant origon insecticides against gram caterpillar, Heliothis armigera Hubn. Indian J. Entomology, 45: 211-212.
Polhill, R.M.(ed.). 1988. Flora of tropical East Africa. Euphorbiaceae I-II. A.A. Balkema, Rotterdam.
Poswal, M.A.T., Masunga, G., Javaid, T. and Kwerepe, B.C. 1992. Comparative evaluation of the inhibitory effects of different plant extracts on the charcoal rot pathogen Macrophomina phaseolina in Botswana. In Mathodi, S.M. et al. (eds.) Proceedings of the first national workshop on plant genetic resources, 24-26 June, 1992, Gaborone.
Rees, D.P., Dales, M.J. and Golob, P. 1993. Alternative methods for the control of stored-product insect pests. A bibliographic Database. Chatham, United Kingdom: Natural Resources Institute.
Rosenthal, G.A. and Janzen, D.H. (eds). 1979. Herbivores: their interaction with secondary plant metabolites. Academic Press, New York.
Saxena, R.C. 1993. Neem as a source of natural insecticides - an update. In Botanical pesticides in integrated pest management. Indian Society of Tobacco Science, 1-24, Rajahmundry, India. IRRI, Manilla, Philippines.
Saxena, R.C., Jilani, G. and Kareem, A.A. 1989. Effects of neem on stored grain insects. In Jacobson (ed.) Focus on phytochemical pesticides. Volume I. The neem tree. CRC Press, Boca Raton, Florida.
Schmutterer, H. 1990. Properties and potential of natural pesticides from the neem tree, Azadirachta indica. Annu. Rev. Entomol. 35: 271-97.
Schmutterer, H., Ascher, K.R.S. and Rembold, H. (eds.). 1981. Natural pesticides from the neem tree (Azadirachta indica) Rottach-Egern Neem Conference, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), Eshborn, Germany.
Schmutterer, H. and Ascher, K.R.S. (eds.). 1984. Natural pesticides from the neem tree (Azadirachta indica A. Juss) and other tropical plants. Proceedings of the second international neem conference, Rauischholzhausen, Germany, 25- 28 May, 1983. GTZ, Eschborn, Germany.
Schmutterer, H. and Ascher, K.R.S. (eds.). 1987. Natural pesticides from the neem tree and other tropical plants. Proceedings from the third international neem conference, Nairobi, Kenya, 10-15 July 1986. GTZ, Eschborn, Germany.
Segeren, P. 1993. Pesticidas naturais: uma alternativa para o sector familiar? Extra - Revista para o desenvolvimento e a extensão rural, 12: 34-38. Centro de Formação Agrária e de Desenvolvimento Rural, Maputo, Moçambique.
Siddiqui, M.A. and Alam, M.M. 1988a. Effect of seed dressing with plant latex on Tylenchorynchus brassicae and plant growth of cabbage and cauliflower. Pakistan J. of Nematology, 6: 65-71.
- 1988b. Effect of latex on Rotylenchus reniformis and plant growth of some vegetables. Nematologia Mediterranea, 16:129-130.
Singh, R.P. 1987. Comparison of antifeedant efficacy and extract yields from different parts and ecotypes of neem (Azadirachta indica A. Juss) trees. In Schmutterer and Ascher (eds.) Natural pesticides from the neem tree and other tropical plants, pp. 185-194. GTZ, Eschborn, Germany.
Sohati, P.H. and Sithanantham, S. 1992 Exploratory field testing of plant extracts against some pests on cowpea in Zambia. Paper presented at the SADCC/IITA Cowpea Workshop for Southern Africa, 26-27 September, 1991, Harare, Zimbabwe.
Stoll, G. 1988. Natural plant protection in the tropics. AGRECOL, Margraf Publishers Scientific Books, Weikersheim, Germany.
Tierto Niber, B. 1989. Evaluation of some indigenous Ghanaian plants for insecticidal, repellent or antifeedant effects on four species of stored product pests. MS-thesis, Dept of Applied Zoology, University of Helsinki, Finland.
Tierto Niber, B., Helenius, J. and Varis, A.-L. 1992. Toxicity of plant extracts to three storage beetles (Coleoptera). J. Appl. Ent. 113: 202-208.
Watt, J.M. and Breyer-Brandwijk, M.G. 1962. The medicinal and poisonous plants of southern and eastern Africa. Livinstone, London.
Weaver, D.K., Dunkel, F.V., Ntezurubanza, L. Jackson, L.L. and Stock, D.T. 1991. The efficacy of linalool, a major component of freshly-milled Ocimum canum Sims (Lamiaceae), for protection against postharvest damage by certain stored product Coleoptera. J. of Stored Products Research, 27: 213-220.
WHO. 1990. Public health impact of pesticides used in agriculture. World Health Organization, Geneva, Switzerland.
Javaid, I. Botswana College of Agriculture, Faculty of Agriculture, Sebele, Private Bag 0027, Gaborone
Manthe, C.S. Dept of Agricultural Research (DAR), Sebele Agricultural Research Station, Private Bag 0033, Gaborone
Mosupi, P.O.P. Plant Protection Division, Ministry of Agriculture, Gaborone
Motshwari, O. DAR, Sebele Agricultural Research Station, Private Bag 0033, Gaborone
Phoebe, D. DAR, Sebele Agricultural Research Station, Private Bag 0033, Gaborone
Yebuah, S. Dept of Chemistry, University of Botswana, Gaborone
Taylor, F.W. Veld Products Research, Gaborone
Segeren, P. Departamento de Sanidade Vegetal, Ministério de Agricultura, C.P. 3658, Maputo
Elwell, H.A. 2, Loerie Lane, Borrowdale, (previous Agritex, P.O. Box BW 330, Borrowdale), Harare
Giga, D.P. Crop Science Department, Faculty of Agriculture, P.O. Box MP 167, Mount Pleasant, Harare
Kutywayo, D. Coffee Research Institute, P.O. Box 61, Chipinge
Muchay, S. Permaculture Association of Zimbabwe (PAZ), Fambidzania Training Centre, Dovedele Road, Mount Hampden, P.O.Box 8515, Causeway, Harare
Mvumi, B.M. Crop Science Department, Faculty of Agriculture, P.O. Box MP 167, Mount Pleasant, Harare
Bwalya, A. Fort Hares' Florist Garden, P.O. Box 450018, Mpika
Chisenga, A. Department of Agriculture, P.O. Box 850007, Serenje
Chitekwele, L. Plant Protection Unit, Mount Makulu research Station, P.O. Box 7, Chilanga
Dudding, J. Institute of Cultural Affairs, P.O. Box 31454, Lusaka Fischer, Family Farms Ltd., P.O. Box 42, Magoye
Kanyemba, M.M. Department of Agriculture, P.O. Box 910067, Mongu
Kaposhi, C.K.M. National Council for Scientific Research, Livestock and Pest Research Centre, P.O.Box 350049, Chilanga
Karlsson, T. Adaptive Research Planning Team, Luapula Regional Research Station, P.O. Box 710129, Mansa
Lesseps, R.S.J. Kasisi Agriculture Training Centre, P.O. Box 30652, Lusaka 10101
Mandola, K.B. District Forestry Extension Office, P.O. Box 80441, Kabwe
Mugoya, C.F. ICIPE Pestnet Project, Mt Makulu Research Station, P.O. Box 7, Chilanga
Mulenga, R.C. ICIPE Pestnet Project, Mt Makulu Research Station P.O. Box 7 Chilanga
Siamngika, University of Reading, Early Gate TB0l, Reading, Berkshire RG6 2AT
Simfukwe, W.M. Deptment of Agriculture, P.O. Box 210612, Chililabombwe
Sohati, P.H. Msekera Regioal Research Station, P.O. Box 510089, Chipata
Chogo, J.B. Tropical Pest Research Institute (TPRI), P.O. Box 3024, Arusha
Ijani, A.S.M. Sokoine University of Agriculture (SUA), P.O. Box 3062, Morogoro
Kaijas, K.A., Handeni Integrated Agroforestry Project (HIAP), P.O. Box 183, Handeni
Kaoneka, B. The International Centre of Insect Physiology and Ecology (ICIPE), P.O. Box 30772, Nairobi, Kenya
Lana, A.F. SUA, P.O. Box 3062, Morogoro
Minja, E.M. TPRI, P.O. Box 3024, Arusha
Mushobozy, D.M.K. SUA, P.O, Box 3062, Morogoro
Mvungi, E.I. Natural Resource Konla, BAP Office, P.O. Box 91, Kondoa
Ramdohr, von A. HIAP, P.O. Box 183, Handeni
Said, M.R. Ministry of Livestock and Natural Resources, P.O. Box 159, Zanzibar
Saidi, J. TPRI, P.O. Box 3024, Arusha
Tierto Niber, B. Dept of Applied Zoology, University of Helsinki, P.O. Box 27, Fin-00014 Helsinki, Finland
Senkondo, F. SUA, P.O. Box 3062, Morogoro
Jro, O. The District Agricultural Officer, Kilifi District, P.O. Box 19, Kilifi
Hassanali, A. The International Institute of Insect Physiology and Ecology (ICIPE), P.O. Box 30722, Nairobi
Kenyan Institute of Organic Farming, P.O. Box 34972, Nairobi
Saxena, K.N. ICIPE, P.O. Box 30722, Nairobi
Songe, C.N. African Centre for Technology Studies, P.O. Box 45917, Nairobi
Association for Social Economic Progress, P.O. Box 14369, Mengo, K'la
Brehony, E. CONCERN, P.O. Box 1644, Masaka
Abate, T. Institute Of Agricultural Research (IAR), p.o. Box 2003, Addis Ababa
Ayele, A. South Wollo, P.O. Box 303, Dessie
Giorgis, M. P.O. Box 408, Makele
Negasil, F. Nazret Research Station, IAR, Nazret
Tekle, F. P.O.Box 16, Robe, Arsi
Jabang, M. Sifoe Kafoo Farm, c/o Sifoe Primary School, P.O. Box 2270, Banjul
Cobbinah, J.R. Forestry Research Institute of Ghana, University, P.O. Box 63, U.S.T, Kumasi
Ahmed, S. Resource Systems Institute (RIC), East-West Centre, Honolulu, Hawai, United States
Dales, M.J. Natural Resources Institute, Central Avenue, Chatham Maritime, Kent, ME4 4TB, United Kingdom
Grainge, M. RIC, East-West Centre, Honolulu, Hawai, U.S.
Ponte, DA J.J. Phytopatologist, Universidade Federal do Ceara, Brazil (working on fungicidal and insecticidal effects of root extracts from cassava)
Stoll, G. Miseror, Mozartstr. 9, 52064 Aachen, Germany
Aconitum ferox (Indian aconite) Ranunculaceae
Acorus calamus (Sweetflag) Araceae
Ageratum conyzoides (Goatweed) Asteraceae
Aleurites fordii (Tung tree) Euphorbiaceae
Annona reticulata (Custard apple) Annonaceae
Annona squamosa (Sugar apple) Annonaceae
Arachis hypogaea (Peanut) Fabaceae
Artabotrys hexapetalus (Ylang-Ylang) Annonaceae
Azadirachta indica (Neem tree) Meliaceae
Chrysanthemum cinerariifolium (Pyrethrum) Asteraceae
Croton tiglium (Purging cotton) Euphorbiaceae
Datura metel (Angel's trumpet) Solanaceae
Datura stramonium (Jimsonweed) Solanaceae
Derris elliptica (Derris) Fabaceae
Haplophyton cimicidium (Cockroach plant) Apocynaceae
Justicia adhatoda (Malabar nut tree) Acanthaceae
Madhuca indica (Mowra) Sapotaceae
Mammea americana (Mammey apple tree) Clusiaceae
Melia azedarach (Chinaberry, Persian lilac) Meliaceae
Mundulea suberosa (Sweetcane) Fabaceae
Nicotiana rustica (Wild tobacco) Solanaceae
Nicotiana tabacum (Tobacco) Solanaceae
Pachyrhizus erosus (Chinese yam bean) Fabaceae
Piper nigrum (Black pepper) Piperaceae
Pogostemon patchouli (Patchouli) Lamiaceae
Pongamia pinnata (Poonga oil tree) Fabaceae
Quassia amara (West Indian quassia) Simaroubaceae
Ricinus communis (Castor bean) Euphorbiaceae
Ryania speciosa (Not known) Flacourtiaceae
Schoenocaulon officinale (Sabadilla) Liliaceae
Tagetes erecta (African marigold) Asteraceae
Tagetes patula (French marigold) Asteraceae
Tephrosia virginiana (Devil's shoestring) Fabaceae
Tephrosia vogelii (Vogel tephrosia) Fabaceae
Tripterygium forrestii (Three-winged nut) Celastraceae
Tripterygium wilfordii (Thunder-god vine) Celastraceae
Veratrum album (European white hellebore) Liliaceae
Veratrum viride (American false hellebore) Liliaceae
Vitex negundo (Indian privet) Verbenaceae
Zanthoxylum clava-herculis (Southern prickly ash) Rutaceae
Zingiber officinale (Ginger) Zingiberaceae
Tidskrift/serie: Rapport - Sveriges lantbruksuniversitet, Institutionen för växtskyddsvetenskap
Utgivare: SLU, Institutionen för växtskyddsvetenskap
Författare: Berger A.
Adress: Department of Entomology, Swedish University of Agricultural Sciences, P.O. Box 7044, S-750 07 Uppsala, Sweden
Titel: Using natural pesticides: current and future perspectives. A report for the Plant Protection Improvement Programme in Botswana, Zambia and Tanzania
Nummer (ISBN, ISSN): ISSN 1104-6422