Larvicidal activity of methanolic leaf extracts of solanum aculeastrum on mosquito larvae

Abstract

Mosquitoes are pestiferous vectors responsible for the transmission of various dreadful diseases like malaria and yellow fever, causing millions of deaths every year. Indiscriminate use of chemical insecticides has resulted in the development of resistance by these organisms, resulting in rebounding vectorial capacity. Traditional Ugandan system of medicine mentions goat bitter apple (Solanum aculeastrum) to have many medicinal properties. So, the present study was to assess the larvicidal ability of the aqueous extracts of ten medicinal plants against mosquito larvae. Six third and fourth instar larvae, each were introduced into treatment trays containing 15 ml of their natural growth medium. To the treatment set, respective concentrations of the plant extracts (0.4, 0.8, 1.2, 1.6 ml) were added from the stock solution; maintaining a relative concentration of the plant extract as 2, 4, 6, 8mg/ml respectively. A control was maintained, containing only larvae and natural growth medium. Mortality counts of larvae were monitored at regular intervals i.e. 6, 12, and 24Hours after treatment. Larvae were considered dead if they settle and remain motionless in the bottom of the test beaker with no response to light or mechanical stimulus or not recovering life functions even after being transferred to their growth medium. It was found that the crude methanolic bitter apple leaf extract showed significant larvicidal effect at different concentrations, hence can be safely used as a potent larvicidal agent. LC50=3.02mg/ml LC90=33.11mg/ml. There was a strong correlation between mortalities observed in larvae and extract concentration. As the leaf extract of Solanum aculeastrum is highly toxic even at low doses this plant may eventually prove to be a useful larvicide. Further analysis is required to isolate the active principles and optimum dosages, responsible for larvicidal activity. This plant would be eco-friendly and may serve as a suitable alternative to synthetic larvicides as they are relatively safe, inexpensive and are readily available in many areas of the world.