Essential oils of six plants growing in Kenya were screened for repellent activities against Anopheles gambiae sensu stricto. The oils of Conyza newii (Compositeae) and Plectranthus marrubioides (Labiateae) were the most repellent (RD50=8.9 x 10(-5) mg cm(-2), 95% CI) followed by Lippia javanica (Verbenaceae), Lippia ukambensis (Verbenaceae), Tetradenia riparia, (Iboza multiflora) (Labiateae) and Tarchonanthus camphoratus (Compositeae). Eight constituents of the different oils (perillyl alcohol, cis-verbenol, cis-carveol, geraniol, citronellal, perillaldehyde, caryophyllene oxide and a sesquiterpene alcohol) exhibited relatively high repellency. Four synthetic blends of the major components (present in > or = 1.5%) of the essential oils were found to exhibit comparable repellent activity to the parent oils.

Volatile oils extracted by hydrodistillation from six plant species growing in the Kenyan coast, Croton pseudopulchellus Pax, Mkilua fragrans Verdc. (Annonaceae), Endostemon tereticaulis (poir.) Ashby, Ocimum forskolei Benth., Ocimum fischeri Guerke and Plectranthus longipes Baker (Labiateae), were evaluated for repellency on forearms of human volunteers against Anopheles gambiae sensu stricto. All oils were found to be more repellent (RC50 range = 0.67-9.21 x 10(-5) mg cm(-2)) than DEET (RC50 = 33 x 10(-5) mg cm(-2)). The individual components of the oils were identified by GC-MS and GC co-injections with authentic standards.The repellency of 15 of the main constituents of the different oils (which had not been previously assayed) was evaluated. Although some of these showed relatively high individual repellencies, none was comparable to the parent essential oils. Partial synthetic blends of selected constituents with moderate or relatively high individual repellency against the vector were also assayed. Four of these exhibited activities comparable to or higher than those of the corresponding parent oils, indicating interesting blend effects in the repellent action of the oils against the mosquito. The implication of these results in the utilization of the plants is discussed.

We are attempting to develop cost-effective control methods for the important vector of sleeping sickness, Glossina fuscipes spp. Responses of the tsetse flies Glossina fuscipes fuscipes (in Kenya) and G. f. quanzensis (in Democratic Republic of Congo) to natural host odours are reported. Arrangements of electric nets were used to assess the effect of cattle-, human- and pig-odour on (1) the numbers of tsetse attracted to the odour source and (2) the proportion of flies that landed on a black target (1×1 m). In addition responses to monitor lizard (Varanus niloticus) were assessed in Kenya. The effects of all four odours on the proportion of tsetse that entered a biconical trap were also determined. Sources of natural host odour were produced by placing live hosts in a tent or metal hut (volumes≈16 m3) from which the air was exhausted at ∼2000 L/min. Odours from cattle, pigs and humans had no significant effect on attraction of G. f. fuscipes but lizard odour doubled the catch (P<0.05). Similarly, mammalian odours had no significant effect on landing or trap entry whereas lizard odour increased these responses significantly: landing responses increased significantly by 22% for males and 10% for females; the increase in trap efficiency was relatively slight (5–10%) and not always significant. For G. f. quanzensis, only pig odour had a consistent effect, doubling the catch of females attracted to the source and increasing the landing response for females by ∼15%. Dispensing CO2 at doses equivalent to natural hosts suggested that the response of G. f. fuscipes to lizard odour was not due to CO2. For G. f. quanzensis, pig odour and CO2 attracted similar numbers of tsetse, but CO2 had no material effect on the landing response. The results suggest that identifying kairomones present in lizard odour for G. f. fuscipes and pig odour for G. f. quanzensis may improve the performance of targets for controlling these species.