Chemical composition and insecticidal activity of plant essential oils from Benin against Anopheles gambiae (Giles)

BACKGROUND: Insecticide resistance in sub-Saharan Africa and especially in Benin is a major public health issue hindering the control of the malaria vectors. Each Anopheles species has developed a resistance to one or several classes of the insecticides currently in use in the field. Therefore, it is urgent to find alternative compounds to conquer the vector. In this study, the efficacies of essential oils of nine plant species, which are traditionally used to avoid mosquito bites in Benin, were investigated. METHODS: Essential oils of nine plant species were extracted by hydrodistillation, and their chemical compositions were identified by GC-MS. These oils were tested on susceptible “kisumu” and resistant “ladji-Cotonou” strains of Anopheles gambiae, following WHO test procedures for insecticide resistance monitoring in malaria vector mosquitoes. RESULTS: Different chemical compositions were obtained from the essential oils of the plant species. The major constituents identified were as follows: neral and geranial for Cymbopogon citratus, Z-carveol, E-p-mentha-1(7),8-dien-2-ol and E-p-mentha-2,8-dienol for Cymbopogon giganteus, piperitone for Cymbopogon schoenanthus, citronellal and citronellol for Eucalyptus citriodora, p-cymene, caryophyllene oxide and spathulenol for Eucalyptus tereticornis, 3-tetradecanone for Cochlospermum tinctorium and Cochlospermum planchonii, methyl salicylate for Securidaca longepedunculata and ascaridole for Chenopodium ambrosioides. The diagnostic dose was 0.77% for C. citratus, 2.80% for E. tereticornis, 3.37% for E. citriodora, 4.26% for C. ambrosioides, 5.48% for C. schoenanthus and 7.36% for C. giganteus. The highest diagnostic doses were obtained with S. longepedunculata (9.84%), C. tinctorium (11.56%) and C. planchonii (15.22%), compared to permethrin 0.75%. A. gambiae cotonou, which is resistant to pyrethroids, showed significant tolerance to essential oils from C. tinctorium and S. longepedunculata as expected but was highly susceptible to all the other essential oils at the diagnostic dose. CONCLUSIONS: C. citratus, E. tereticornis, E. citriodora, C. ambrosioides and C. schoenanthus are potential promising plant sources for alternative compounds to pyrethroids, for the control of the Anopheles malaria vector in Benin. The efficacy of their essential oils is possibly based on their chemical compositions in which major and/or minor compounds have reported insecticidal activities on various pests and disease vectors such as Anopheles

Inventaire ethno-pharmacologique des plantes utilisées dans le traitement des pathologies parasitaires dans les élevages extensifs et semi-intensifs du Bénin

L’Afrique regorge d’une importante réserve de plantes utilisées en  ethnomédecine vétérinaire. La présente étude vise à répertorier une gamme de plantes médicinales habituellement utilisées pour traiter lespathologies parasitaires des animaux. A cet effet, une enquête ethno-botanique a été réalisée auprès de 787 éleveurs et agro-éleveurs des huit zones agro-écologiques du Bénin, de juin à décembre 2013. Au total, cinq (5) plantes médicinales (Azadirachta indica, Cajanus cajan, Cissus  quadrangularis, Nicotiana tabacum et Vernonia amygdalina) sont utilisées pour traiter la coccidiose contre deux (2) plantes (Bombax costatum etProsopis africana) pour la piroplasmose et douze (12) plantes dont A. polyacantha, C. sieberiana, C. febrifuga, D. microcarpum, P. kotschyi, Z. mays pour la trypanosomiase. En outre, dix-huit (18) plantes dont A. digitata, A. senegalensis, A. leiocarpa, Bambusa vulgaris, F. exasperata ont été inventoriées pour traiter les ectoparasitoses contre dix-sept (17) plantes dont A. flagellaris, C. papaya, E. guineensis, M. charantia, Sennaalata pour la gale et quarante-deux (42) plantes dont A. digitata, A. sativum, Anacardium occidentale, A. leiocarpa, B. ferruginea, C. papaya, C. ambrosioides, K. senegalensis, F. sur, M. inermis, N. canensis pour traiter les helminthiases. Les organes les plus utilisés sont les feuilles et les écorces. La majorité des remèdes sont préparés sous forme de décoction. Des tests sur l’efficacité de ces plantes permettront de mieux les valoriser dans la lutte contre les pathologies parasitaires.Mots clés : Maladies parasitaires, phyto-pharmacologie, enquête, Bénin