Root bark extracts of five Meliaceae species (Turraea abyssinica Hochst., Turraea wakefeldii Oliv., Turraea mombassana Hiern ex C.DC., Trichilia roka (Forsk) Chiov. and Melia volkensii Guerke.) and different fractions thereof (following chloroform extraction and column chromatographic separation) were compared for their immediate toxicity and long-term effects on Anopheles gambiae Giles sensu stricto (Diptera: Culicidae). Larvicidal effects of the extracts appeared to be largely associated with limonoids of medium polarity with M. volkensii and T. mombassana extracts being more potent than those of the other Meliaceae. Long-term (6–8 days post-exposure) observations at lower doses showed that 100% cumulative mortality can be achieved with some extracts (particularly those of T. mombassana and M. volkensii) with interesting growth-inhibition effects. Follow-up studies that are needed and practical implications of the results in terms of development of larval control strategies for African malaria vectors are discussed.

A method of formulating granules from an acetone extract fraction of the fruit of Melia volkensii, a Kenyan tree known to possess insecticidal properties, was developed. The granules were tested for toxicity to third and fourth instars of Aedes aegypti L. Some acute physiological effects were observed within 24 hours of adding the granules to water as larval food. A mortality of 95% was achieved on various developmental stages of the mosquito after 12 days, with only 5% adult emergence being recorded.

A chromatographically enriched fraction designated Fraction B from dry fruits of the plant Melia volkensii (family Meliaceae) was evaluated with the objective of determining its toxic and growth inhibiting effects on the larvae and adults of Culex quinquefasciatus mosquitoes. The fraction was purified from a crude methanolic extract by cold precipitation and elution of the precipitate dissolved in a hexane-ethyl acetate solvent system through a silica gel column. Larval treatments involved rearing the larval stages in water containing the fraction at concentrations of between 5 and 200 ppm. The LC50 for this fraction was found to be 34.72 μg/ml in 48 h. Second instar larvae were found to be more susceptible to fraction B when compared to fourth instar larvae. All fourth instar larvae that survived the treatment moulted into larval-pupal intermediates that were short-lived. The extract was also found to be an oviposition deterrent at a concentration of 20 ppm and above. It is concluded that M. volkensii extract has potential in the control of Culex quinquefasciatus.