author(s)
Lame Younoussa, Charles Okechuckwu Esimone, Simon Pierre Yinyang Danga, Theodora Kopa Kowa and Elias Nchiwan Nukenine

abstract
The repeated and misuse of synthetic insecticides for mosquito control has raised the problem of human toxicity, environmental pollution and insect resistance, and the search for alternative mosquito control methods using botanicals is nowadays warmly encouraged. For that, the methanolic crude extracts, fractions (n-hexane, chloroform, ethylacetate and methanol) and essential oils of the leaves of Annona senegalensis and Boswellia dalzielii were essayed for their toxic properties against the adults of Anopheles gambiae, Aedes aegypti and Culex quinquefasciatus in the laboratory using CDC bottles method. The plant extracts and fractions were applied at doses of 312.5, 625, 1250 and 2500 mg/bottle while essential oils were tested at the concentrations ranging from 25 to 200 mg/bottle on adults of the three mosquito species. DDVP (2.2-dichlorovinyl dimethyl phosphate, 2000 mg/bottle) and acetone (1mL) were used as positive control and negative controls, respectively. Mosquito mortality was monitored after 24 h post-exposure plant extracts/fractions and 1, 6, 12, 18 and 24 h post-treatment for essential oils. In results, extracts and fractions of the two plant species caused a moderate mortality of the three mosquito species adults and the significant mortality (≥ 60%) was obtained with n-hexane fraction of the two plants against An. gambiae adults. The n-hexane fractions of A. senegalensis (1636.39 mg/bottle) and B. dalzielii (1836.7 mg/bottle) were the most potent against An. gambiae compared to other fractions and the two other mosquito species. Essential oils of the two plant species tested at 200 mg/bottle as well as DDVP (2000 mg/bottle) achieved complete mortality (100%) of the three mosquito species. LC50 values recorded after 24h post-treatment were 2.15, 12.23 and 13.44 mg/bottle for A. senegalensis and 7.33, 11.34 and 8.95 mg/bottle for B. dalzielii, respectively against An. gambiae, Ae. aegypti and Cx. quinquefasciatus mosquito adults. Thus, n-hexane fraction and essential oils of A. senegalensis and B. dalzielii could be a source of safe and very potent insecticidal products for the preparation of traditional or refined insecticide formulations for mosquito control.