Laboratory evaluation of spinosad as a potential larvicide against immature forms of Aedes aegypti

Abstract

Background and Objectives: Aedes mosquito has been recognized as a global emerging threat with its potential to transmit fatal diseases of international public health importance such as dengue, chikungunya, and yellow fever. Prior attempts to manage the vector with various synthetic larvicides have resulted in emergence of resistance, thus necessitating search for a safer and effective alternative. The study was an experimental laboratory-based study to screen the recent World Health Organization (WHO)-approved insecticide spinosad for larvicidal activity and compare the efficacy of the same with other currently used larvicides, namely temephos and Bacillus thuringiensis var. israelensis (Bti). Methodology: An experimental setup was done as per the WHO Pesticide Evaluation Scheme to assess the larvicidal activity of the spinosad at varying concentrations along with a positive and negative control. A preliminary screening to assess the larvicidal property of the spinosad was undertaken with 0.5 ppm concentration as recommended by the WHO. The mortality was checked after 24 h and results were statistically analyzed and LC50 and LC90 values were calculated. Results: Spinosad brought about 100% larval mortality at the recommended dosage (0.5 ppm) as well as at a lower dosage of 0.1 ppm. The comparison with the other two commonly used larvicides, namely temephos and Bti, reveals 100% and 90% mortality, respectively, in wild Aedes larvae. Conclusion: The study concludes that spinosad is a promising larvicide that can be used in rotation with temephos against Aedes aegypti in potable water and may be used at a lower dosage of 0.1 ppm. However, large-scale field trials are required to ascertain the effectiveness of the larvicide in field conditions.