Farmers’ ethno-ecological knowledge of vegetable pests and pesticidal plant use in Malawi and Zambia

While pests are a major constraint in vegetable production in many parts of Southern Africa, little is known about farmers’ knowledge and management practices. A survey was conducted among 168 and 91 vegetable farmers in Northern Malawi and Eastern Zambia, respectively, to evaluate their knowledge, attitudes and traditional management practices in tomato and crucifers (brassica). All respondents in Malawi and Zambia reported pest damage on tomato and crucifers, and 75% had used synthetic pesticides. The use of pesticidal plants, cultural practices and resistant varieties constituted a smaller portion of the pest control options in both crucifers and tomato. Over 70% of the respondents were aware of pesticidal plants, and more female (75%) than male (55%) respondents reported using them. While over 20 different plant species were mentioned by respondents, Tephrosia vogelii accounted for 61 and 53% of the pesticidal species known to respondents in Malawi and Zambia, respectively. Farmers with small landholdings were more inclined to use pesticidal plants than those with medium and large landholding highlighting the importance of this management alternative for poor farmers. Most respondents were willing to cultivate pesticidal plants, which indicate that farmers understand the potential value of these plants in pest management

Chemical variation and insecticidal activity of Lippia javanica (Burm. F.) Spreng essential oil against Sitophilus zeamais Motschulsky

Lippia javanica (Burm. f.) Spreng is used commercially as an herbal tea and medicinal plant in sub-Saharan Africa. Here we investigated the chemical variation and pesticidal potential of L. javanica essential oils against a major stored product pest, Sitophilus zeamais Motschulsky. We identified two morphologically distinct varieties of L. javanica growing at different locations in Malawi. Perillaldehyde was the major constituent in oil of L. javanica var. javanica while myrcenone (ipsdienone) was the major compound in oils of L. javanica var. whytei. Myrcene, linalool, carvone, β-caryophyllene and germacrene D were identified as the other most significant components in oils from both varieties. The yields of oil and the chemical composition also varied significantly with time of harvest during the season in both cases. In contact toxicity tests against S. zeamais, oils from both varieties were active. However, whereas perillaldehyde, linalool and carvone, components of the oil of L. javanica var. javanica, were all toxic against adult S. zeamais, myrcenone, the main component of oil from L. javanica var. whytei, was not. The oil from L. javanica var. javanica also showed some fumigant toxicity against S. zeamais. The high efficacy of L. javanica oil against S. zeamais suggests it is suitable to be used as a botanical insecticide to control S. zeamais in stored maize. However, further research is required to optimise and standardise the variety and harvest time to be recommended and to evaluate its activity against S. zeamais and other storage insect pests under farm conditions before it can be adopted by farmers more widely

Highly variable insect control efficacy of Tephrosia vogelii chemotypes

Tephrosia vogelii has been used for generations as a pest control material in Africa. Recently, two chemotypes have been reported based on the occurrence (chemotype 1) or absence (chemotype 2) of rotenoids. This could have an impact on the efficacy and reliability of this material for pest control. We report that chemotype 2 has no pesticidal activity against Callosobruchus maculatus Fabricius (family Chrysomelidae) and that this is associated with the absence of rotenoids. We present a first report of the comparative biological activity of deguelin, tephrosin, α-toxicarol, and sarcolobine and show that not all rotenoids are equally effective. Tephrosin was less toxic than deguelin which was less active than rotenone, while obovatin 5-methyl ether, the major flavonoid in chemotype 2 was inactive. We also report that in chemotype 1 the occurrence of rotenoids shows substantial seasonal variation

Optimising pesticidal plants in Africa: technology innovation, outreach and networks

Small-holder farming in Africa is marginal and at risk of failure through losses due to biotic and abiotic factors. Invertebrate pests are perhaps the most important biological stress since pest control technologies are usually straightforward even for resource poor farmers and the effects of control are easily seen. Synthetic pesticides are used widely but are, however, expensive, frequently adulterated (so lose efficacy), are often out of date or are toxic, are not always available, may be used incorrectly and are persistent in the environment. Pesticidal plants are a low cost and effective alternative, and many small-holder farmers in Africa depend on them entirely for controlling invertebrate pests of stored products, field crops and livestock. However, chemical variability in some species, limited natural availability of plants and inefficient application methods mean there is considerable scope for optimising their safe use. We have developed a network of universities, NGOs, government institutions and private sector over several years and are enabling researchers in Africa to understand how best to use plants based on robust scientific evidence of the chemistry and efficacy and impacts on non-target species. Our work is now developing technologies for improved food security based on pesticidal plants that can be effectively deployed within the context of local needs and resources. We are also developing protocols for the propagation and cultivation of key species to improve availability and increase opportunities for commercialisation. Capacity building for stakeholders is critical to successful and sustainable uptake but users need to fully understand the policies that govern their use and the most effective and efficient applications in pest management and food security. An understanding of the policy environment is required to develop commercial opportunities at both the large and small scale to enhance our promotion strategies widely for optimised and safe use