Screening for adulticidal bioactivity of South African plants against Anopheles arabiensis.

Background: This study was conducted to evaluate whether a selection of South African ethnomedicinal plants included in this study displayed insecticidal properties when screened against adult stages of the mosquito.

Methods: 381 crude extracts of 80 plant taxa in 42 families were sprayed onto ceramic tiles and screened using the cone bio-assay method for insecticide efficacy testing. Blood-fed, female Anopheles arabiensis mosquitoes were exposed to the treated tiles for a period of sixty minutes. Mosquito mortality was monitored for twenty-four hours.

Results: Of all the extracts analysed, the highest activity was observed in Ptaeroxylon obliquum (Ptaeroxylaceae) and Pittosporum viridiflorum (Pittosporaceae), a single extract from each, exhibiting more than 50% mortality. A large proportion (81.63%) of the extracts tested displayed low levels of mosquitocidal activity. The remainder of the extracts (17.85%) exhibited no bioactivity (0% mortality).

Conclusions: The screening results have shown that in accordance with WHO standards, none of the crude extracts tested had exhibited greater than 60% mortality against the adult stages of the malaria vector Anopheles arabiensis.