2004

Simiyu Silas Khamala B.Sc.
Bioevaluation of Insecticidal and Repellent Plants from Central Region of Kenya and Chemical Identification of Bioactive Derivatives
A thesis submitted in partial fulfilment for the award of the degree of Master of Science of Kenyatta University, Nairobi, Kenya

Bioevaluation of Insecticidal and Repellent Plants from Central Region of Kenya and Chemical Identification of Bioactive Derivatives

Abstract :

Despite considerable control efforts, malaria still remains the most prevalent and devastating disease in the tropics. With more than 40% of the world population at risk, malaria undermines the welfare of several South American, Asian and African states, endangering the survival of children (killing one child every 30 seconds) and straining scarce resources. It is estimated that US $ 2 billion is spent on malaria control and treatment programmes in Africa annually. The problem is becoming increasingly difficult to manage because of the continuous intensification and spread of resistance to anti-malarial drugs by the parasites. This poses a serious threat in increased severity of disease and health. Vector resistance to insecticides is a recurring theme and a major problem in malaria control programmes. The safety and efficacy of N, N-diethyl-mtoluamide (DEET), the most potent of the modem synthetic repellent, is questionable. Other problems associated with repellents include vector resistance, avoidance and frequent repetitive application. The recent discovery of trans-cis-nepetalactone and p-mentane-3,8-diol that are more effective and environmentally friendly than DEET justifies bioprospecting from plants. In our search for new repellents we have continued with bioprospecting activities of the Kenyan flora.

The essential oils from leaves of Artemisia afra, Senecio moorei, Cineraria grandifolia (Asteraceae), Nepeta azurea, Satureja pseudomensis (Labitae), Clausena anisata (Rutaceae) and Pseudocarum eminii (Umbelliferae) from Mt. Kenya region were evaluated for their repellent and insecticidal activity against adult female An. gambiae mosquitoes. The essential oil of Nepeta azurea was the most effective repellent (RD50 6.5x10-7mg/cm2). The essential oils from other species studied also showed significant repellent effect. The order of repellency was : Pseudocarum eminii > Senecio moorei > Clausena anisata > Satureja pseudomensis > Cineraria grandifolia > Artemisia afra with RD50 = 4.39 x 10-4, 1.27 x 10-3, 7.86 x 10-3, 1.15 x 10-2, 2.2 x 10-2, 3.07 x 10-2 mg/cm-2, respectively. The essential oil from Artemisia afra was insecticidal at 1% w/v (LD50= 2.26x 10-2 mg/cm"). The constituent compounds were identified through GC, GC-MS and GC co-injection and bio-assayed for repellent and insecticidal properties.

Excerpt :

23.1.1.1 Artemisia afra
Artemisia afra from the family Asteraceae is described as an erect loose shrub to 2 m, with grey-green aromatic foliage. Locally the plant is known by various names such as Sesimwa (Marakwet), Ushemeli (Sukuma) and Shamba (Fiji) (Agnew, 1974). The herb is frequently used in folk medicine for various pharmacological properties (Kokwaro, 1993). A fermentation of the heated herb is given to children with soar throat. The plant is also used for indigestion. Roots are boiled and decotion drunk 2-3 times a day for internal worms. The leaves are chewed and juice swallowed as emetic (Kokwaro, 1993). A. afra was collected from Marania Forest, Mt. Kenya via Timau on the way to the Kenya School of Adventure.

The anti-plasmodial activities against chloroquine-resistant Plasmodium falciparum and mosquito larvicidal activity of the extracts ofA. afra has been reported (Kraft etal., 2003) and (Guantai, 1990) respectively. The essential oil composition of A. afra from S. Africa, Botswana and Zimbabwe has been reported (Graver et al., 1990 ; Chagonda et al., 1999). However, no repellent or adulticidal activity had been undertaken. In our preliminary studies, A. afra oil exhibited both repellent and insecticidal activity against An. gambiae s.s mosquitoes. These findings and the fact that no repellent or insecticidal activity had been reported in the literature for this plant prompted us to embark upon chemical and biological investigations in search of repellent or insecticidal compounds therein.

2017

Laëtitia Machiels
Contribution à l’étude de l’effet d’une culture associée entre l’armoise africaine (Artemisia Afra Jacq. Ex Willd.) et le chou pomme (Brassica Oleracea Var. Capitata L.) sur les ravageurs du chou pomme dans la région de Thies au Sénégal
Travail de fin d’études présenté en vue de l’obtention du diplôme de Master Bioingenieur en bio-ingénierie et sciences agronomiques. Année académique : 2016-2017

Contribution à l’étude de l’effet d’une culture associée entre l’armoise africaine (Artemisia Afra Jacq. Ex Willd.) et le chou pomme (Brassica Oleracea Var. Capitata L.) sur les ravageurs du chou pomme dans la région de Thies au Sénégal

Résumé

De nombreuses études ont montré de meilleurs rendements dans les cultures associées avec des plantes aromatiques résultant de l’émission de composés organiques volatiles (COV) qui induisent un effet sur le comportement des insectes. Afin d’évaluer l’effet de l’association de l’armoise africaine (Artemisia afra Jacq. ex Willd.) avec le chou pommé (Brassica oleracea L. Convar. Capitata (L) Alef. var. Alba DC.) sur les ravageurs et le rendement du chou, un dispositif expérimental en blocs aléatoires complets avec 3 répétitions a été installé dans la région de Thiès au Sénégal. Le but était de comparer trois traitements : (A) culture de chou associé avec A. afra sans traitement insecticide, (B) culture pure de chou sans traitement insecticide et (C) culture pure de chou avec traitement insecticide. Le suivi d’insectes a été réalisé pour les traitements (A) et (B) grâce à 3 pièges collants et aux observations visuelles d’insectes dans 3 quadrats mobiles par parcelle ; 2 fois par semaine pendant 2 mois. Les données de rendement et les dégâts occasionnés sur pommes ont été recensés à la récolte pour les 3 objets durant 5 semaines de récoltes échelonnées. Le prix de revient a été calculé pour chacun des trois traitements. Les principaux ravageurs observés sont Hellula undalis (Fabricius), Plutella xylostella (Linnaeus), Trichoplusia ni(Hübner) et des pucerons. Les résultats ne montrent pas de différence significative pour les populations d’insectes entre les traitements (A) et (B). Le rendement le plus élevé en moyenne est celui du traitement (B) suivi du traitement (C) puis du traitement (A). Finalement, le traitement (A) est le plus rentable grâce au revenu élevé apporté par l’armoise.

Mots clés : Artemisia afra, Brassica oleracea, associations culturales, plantes aromatiques, ravageurs, rendement, prix de revient