Lysinibacillus sphaericus biolarvicide, an efficacious tool in the control of Anopheles gambiae in Kumasi, Ghana

Abstract

Malaria continues to be the leading cause of morbidity and mortality globally. In Ghana control of the vector involves multiple strategies. One of the strategies being adopted is the integrated vector management (IVM) control approach. However, there is evidence of growing resistance by malaria vectors in the country to several classes of insecticides. Therefore interest in alternatives to augment already existing interventions is high. We assessed the effectiveness of Water Dispersible Granular (WDG) formulation of Lysinibacillus sphaericus (also known as Bacillus sphaericus), a biolarvicide, as a tool against Anopheles gambiae Giles complex larvae in the laboratory and controlled field study in Kumasi metropolis, Ghana. The Lethal Concentration (LC) of the biolarvicide to kill 50% (LC₅₀) and 95% (LC₉₅) of first generation (F₁) Anopheles gambiae larvae were determined in the laboratory by a range of bioassays. The optimum effective dosage of Bs VectoLex® formulations against naturally occurring Anopheles gambiae Giles complex larvae was determined in controlled field trials during the rainy and dry seasons. We show here that Anopheles gambiae Giles complex larvae were susceptible to the biolarvicide with LC₅₀ and LC₉₅ of 0.0027 mg/l and 0.0086 mg/l, respectively after 24 hours exposure in the laboratory. The 50 fold concentration of the LC₉₅ were found to achieve 100% larval mortality within 24 hours post-application for up to 10 (dry season) to 12 days (rainy season) under field conditions. There was a highly significant difference (p<0.0001) in larvae population after addition of 0.5 mg/l as compared to the control for both seasons. The biolarvicide proved to be an efficacious tool in the reduction of Anopheles gambiae Giles complex larval population. Further studies need to be carried out to evaluate the impact this biolarvicide in terms of reduction in actual malaria incidence and also assess cost effectiveness of the biolarvicide in relation to other malaria vector control interventions.

Keywords: Lysinibacillus sphaericus, Anopheles, malaria, vector, biolarvicide, Kumasi.