Pengaruh pH dan suhu penyimpanan terhadap aktivitas larvasida Bacillus thuringiensis di laboratorium

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Pengaruh pH dan suhu penyimpanan terhadap aktivitas larvasida Bacillus thuringiensis di laboratorium
The effects of pH and storage temperature on larvicidal activity of Bacillus thuringiensis in the laboratory
JURNAL KEDOKTERAN YARSI 12 (1) : 076-084 (2004)
by
Umi Widyastuti dan Blondine Ch P.
Vector and Reservoir Control Research Unit, Salatiga, Central Java


ABSTRACT
A study was conducted to determine the effects of pH and storage temperature on larvicidal activity of Bacillus thuringiensis in the laboratory. B. thuringiensis was stored in acid, neutral, and alkaline buffers ranging from pH 4 to 11 at 4oC and 25oC, and was then tested against Anopheles aconitus, Culex quinquefasciatus, and Aedes aegypti early fourth instar larvae. The test was conducted according to WHO standard guidelines periodically biweekly until 238 days. Larvicidal activity was calculated based on larval mortality after 24 hours of exposure. The results showed that larvicidal activity remained more than 50 % for B. thuringiensis stored at 4oC and 25oC in neutral buffer (pH 7). This larvicidal activity remained until 238 days for An. aconitus and Cx. quinquefasciatus, and 182 days for Ae. aegypti. The effectivity in neutral buffer was maintained longer compared to acid and alkaline buffer which only maintained an effectivity for 84 -126 days. Larvicidal activity of B. thuringiensis stored at 4oC in neutral buffer was higher than at 25oC, respectively 73.37% for An. aconitus and Cx. quinquefasciatus for 238 days, compared to 59.69% and 63.36% for An. aconitus and Cx. quinquefasciatus stored at 25oC. For Ae. aegypty the same phenomena was shown namely a larval mortality of 53.35% at 4oC compared to 40.02% at 25oC, both for duration of 210 days. The best storage regime for maintenance of larvicidal activity of B. thuringiensis on An. aconitus, Cx. quinquefasciatus, and Ae. aegypti larvae was 4oC in neutral buffer.