ABSTRACT
Larvicidal efficacy of Teknar HP-D, an improved biolarvicidal formulation of Bacillus thuringiensis ssp. israelensis (Bti), against Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti was determined in the laboratory, and in field the efficacy of the formulation was tested against Cx. quinquefasciatus breeding in cesspits, unused wells and drains. The toxicity of the formulation to Gambusia affinis (larvivorous fish), Notonecta sp. and Diplonychus indicus (water bugs) was also evaluated in the laboratory. Teknar HP-D was field tested at three recommended dosages, 1, 1.5 and 2l/ha, selecting five habitats for each dosage. Another five habitats were kept untreated as controls. Ae. aegypti showed greatest susceptibility to the Bti toxin in the laboratory. In cesspits, all the three dosages caused >80% reduction of pupal recruitment up to day 6 post-treatment, indicating that a weekly application at the lowest would be necessary for sustained control. The residual activity of the formulation was longer in unused wells, causing >80% reduction of pupal recruitment for 17 days from the day of treatment. In controlling pupal recruitment the three dosages produced equal effect. Application of Teknar HP-D at 1 l/ha once in three weeks is therefore recommended to control Cx. quinquefasciatus in unused wells. However, in drains, >80% reduction of pupal recruitment was observed for only 3 days and hence, application of Teknar HP-D at 2 l/ha that caused significantly higher level of reduction twice in a week at 3-day interval is necessary. At dosages from 0.032 to 3.2 mg/l (ppm), Teknar HP-D was non-toxic to Gambusia fish. The two predatory water bugs, Notonecta sp. and Diplonychus indicus that fed on the surviving larvae of Cx. quinquefasciatus exposed to the sub-lethal doses (LC(50) and LC(80)) of Teknar HP-D were safe with out having any mortality.
