INVESTIGATION OF THE MOSQUITO LARVICIDAL ACTIVITY OF THE OIL OF MARIGOLDS (TAGETES SPP., AEDES AEGYPTI, OCIMENONE, ALLELOCHEMICS)

Research has shown that plants employ chemical defenses against insect predators. The search for plants which produce potentially useful allelochemicals may be aided by field observations, thereby avoiding lengthy broad spectrum screening experiments. Field observations which form the basis of agricultural folklore, could be used to focus scientific investigation. This stimulated research which supported the folklore claim of the ovipositional repellency of marigold oil to flies (Musca domestica L.). The possible validity of other folklore claims led to the present investigation of the response of the mosquito, Aedes aegypti L. (the disease vector for yellow fever) to possibly afford a control mechanism.;Marigold oil (Tagetes spp.) was obtained by steam distillation from flowering plants grown without pesticides. The oils were characterized by GC and HPLC and monitored for stability. In entomological bioassays with A. aegypti larvae, the oil from T. minuta proved larvicidal. This oil and its ethanolic solutions retained biological activity upon repeated bioassay, after storage at -20(DEGREES)C for up to 24 months. Aqueous solutions incubated at 30(DEGREES)C maintained activity for at least 9 days after preparation. Bioactivity was located in the late-eluting, non-polar HPLC (reversed-phase) chromatographic region of the oil.;The suspected larvicidal principle, suggested by previous work, (5E)-ocimenone (2,6-dimethylocta-2,5,7-trien-4-one) was synthesized. The resultant product composition of cis- and trans-isomers (2:3), determined by HPLC and GC was at variance with previously published results. Further characterization was performed by IR, UV, GC/MS and NMR (proton and ('13)C).;Upon bioassay, fresh solutions of ocimenone at 40 ppm resulted in mortalities comparable to 10 ppm solutions of T. minuta. In sharp contrast to concurrently assayed T. minuta controls ocimenone was found to be unstable upon standing, with subsequent loss of biological activity. Ocimenone does not elute in the HPLC chromatographic region of T. minuta oil where activity was found. T. minuta oil, from which ocimenone had been removed by lyophilization, retained larvicidal activity. A chromatographic region responsible for the activity has been isolated and bioassayed but remains to be further separated and identified.;The use of natural materials, such as marigold oil, may offer advantages in augmenting current mosquito control methodologies.