Influence of Physicochemical Parameters on Mosquito Larvicidal Potency of Bacillus subtilis Isolated from Musca domestica (Linn) Cadavers in Nigeria

Abstract

Aims: Biological control method is one of the methods used in controlling the menace of insect pest because it posed no threat to the human health and less damage to the environment. This study therefore assessed the effect of selected physicochemical parameters on the larvicidal potency of Bacillus subtilis(Berg) on Anopheles arabiensis (Linn) mosquito larvae. Study Design: The physicochemical parameters were considered for this study include; pH, concentration, temperature, turbidity and sunlight.  Place and Duration of Study: This research was carried out in the Department of Microbiology Federal University of Technology, Akure, Nigeria, between May 2013 and September 2013. Methodology: Bacillus subtilis were isolated from cadavers of Musca domestica and it larvicidal potency on Anopheles arabiensis (Linn) mosquito larvae was tested by varying values of each of physicochemical parameters on both the 2nd and 4th instars of laboratory reared Anopheles arabiensis using standard methods. Results: A mortality of 30% was recorded at pH 4.0 while at pH 9.0 higher percentage mortality (81%) was observed on the second instars larvae. Five temperatures of 16°C, 18°C, 24°C, 34°C and 40°C representing four major temperature ranges in southwestern Nigeria (night, morning, afternoon and evening) and control temperature (28±2°C) revealed significant variation in the percentage mortality of mosquito larvae. Varying concentrations of Bacillus subtilis cells showed that the larvicidal activity of this bacterium was best displayed at higher concentrations. The water turbidity and sunlight also affected the effectiveness of the larvicidal activity. Conclusion: This study revealed that Bacillus subtilis was able to demonstrate high larvicidal activity against Anopheles arabiensis larvae despite the varied physicochemical parameters. However, further work may be needed to validate reliability.