Aqueous neem extract versus neem powder on Culex quinquefasciatus: implications for control in anthropogenic habitats

Abstract

Control programs using conventional insecticides to target anthropogenic mosquito habitats are very expensive because these habitats are widespread, particularly in cities of most African countries. Additionally, there are serious environmental concerns regarding large-scale application of most conventional insecticides. Clearly there is a need for alternative methods that are more effective, less expensive, and environmentally friendly. One such method would be the application of preparations made from parts of the neem tree, Azadirachta indica A. Jussieu (Sapindales: Meliaceae). In this study, aqueous crude extracts and crude powder were prepared from different parts of neem, and the efficacies of the preparations on juvenile stages of Culex quinquefasciatus Say (Diptera: Culicidae) were evaluated in the laboratory. When larvae were exposed to a concentration of 0.1 g/mL extract for 24 hours, percent mean mortality (± SE) was 72.7 plusmn; 1.8 for the bark, 68.7 ± 1.6 for fruits and 60 ± 1.6 for leaves. These means were not significantly different (χ(2) = 4.12; df = 2; p = 0.127). At a concentration of 0.01 g/mL, > 95% of the larvae died within 24 hours of exposure to powdered neem leaf, but it took 120 hours to reach the same level of larval mortality in aqueous leaf extract. The crude extract slowly inhibited the growth and development of mosquitoes while the crude powder acted more as a barrier; the mosquitoes probably died from suffocation. However, both types of preparations can be made and used by local people to control mosquito breeding in anthropogenic habitats, especially in urbanized areas.

Figures

Figure 1.

Mean mortality of late larvae of Culex quinquefasciatus within a period of exposure to 0.1 g/mL concentration of crude extract from neem leaves, fruits and bark. Error bars represent 2 SE. High quality figures are available online.

Figure 2.

Mean % mortality of early and late instar of Culex quinquefasciatus after 24-hour exposure to different concentrations of local extract from neem leaves. Error bars represent I SE. High quality figures are available online.

Figure 3A–B.

Mean % mortality of (A) late instar larvae and (B) pupae of Culex quinquefasciatus after 24-hour exposure to fruit and leaf powder at different doses. Error bars represent I SE. High quality figures are available online.

Figure 4.

Mean % mortality of Culex quinquefasciatus larvae after 24-hour exposure to different concentrations of local extract from neem leaves and neem leaf powder. Error bars represent I SE. High quality figures are available online.