Background Abandoned water closets can serve as reservoir habitat for mosquitoes especially the Asian tiger mosquitoes. Botanicals larvicides are among the recommended strategies used in Integrated Vector Management (IVM) of mosquitoes. Biological potency of ashes of scent leaves (Ocimum gratissimum) and lemon grass (Cymbopogon citratus) against larvae of Aedes mosquitoes were assessed.

Methods Aedes albopictus larvae were surveyed and marked in water closet in a university in Niger Delta region of Nigeria. Ashes from the plants were measured in 1g, 2.5g, 5g, 10g and 15g respectively and emptied into the bowl of the closet with stagnant water. Acute and Chronic toxicity were carried out and mortality recorded after 10 to 60 minutes and 6hours to 60 hours respectively. Adult emergence was also used to measure efficacy of treatment.

Results It was observed that larval mortality increased with time in all concentrations of test plants and chronic toxicity showed 100% mortality in all treatments. The 15g of lemon grass concentration recorded the highest mortality of larvae after 30 minutes in the acute toxicity experiment. There was 0% mortality of the larvae in the all the scent leave concentration in the acute toxicity experiment. Lethal time of 50% was 0.58 and 2.7g, and for and 95% was 2.3 and 34.1g for Scent leave and lemon grass ashes respectively (p<0.05).

Conclusion These treatments are therefore considered as good materials for local treatment of abandoned water closets to reduce vector populations and chances of increased biting rates in Africa.