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Combined effect of seaweed (Sargassum wightii) and Bacillus thuringiensis var. israelensis on the coastal mosquito, Anopheles sundaicus, in Tamil Nadu, India

Kanagarajan Prasanna Kumar^a, Kadarkarai Murugan^a,*, Kalimuthu Kovendan^a, Arjunan Naresh Kumar^a, Jiang-Shiou Hwang^b, Donald R. Barnard^c

 
ABSTRACT:     Laboratory studies were made to determine the effectiveness of seaweed (Sargassum wightii) extract combined with Bacillus thuringiensis var. israelensis for the control of Anopheles sundaicus Liston, a malaria vector that occurs in the coastal areas of peninsular India. The results revealed that the different concentrations of crude extract of S. wightii resulted in considerable mortality and the LC₅₀ value for I Instar larvae at 1.0 mg/l was 0.88, for II Instar 0.73, for III Instar 1.34, for IV Instar 1.56, and for pupa 1.71. The LC₉₀ values of I, II, III, and IV Instar, and pupa were 2.73, 2.43, 3.03, 3.21, and 3.23 mg/ml, respectively. Among the larval instars, instar II was the most susceptible. A considerable repellency was noted; a 10 mg/l concentration of S. wightii showed a repellency of 89%. Sea weed extract and B. thuringiensis toxins affected the larval duration and adult emergence. A synergistic factor was also found for the effect of seaweed extract against larvae and pupae of mosquito. The synergistic factor showed at I Instar was 1.74, II Instar was 1.93, III Instar was 1.37, IV Instar was 1.27, and pupa was 1.24, respectively. The result revealed that the seaweed extract of S. wightii in combination with microbial toxins has interfered in the gut system and resulted in mortality as well as growth inhibitory effects on mosquitoes.

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* Corresponding author, E-mail: kmvvk@yahoo.com

Received 16 May 2010, Accepted 22 May 2012