Field evaluation of biolarvicides in Surat city, India

Background & objectives : Two bacterial larvicide (bio-larvicide) formulations—Bac ticide ® and VectoBac ® containing viable endospores and delta endotoxin of Bacillus thuringiensis var israelensis H-14 were evaluated in 2001 for their mosquito larvicidal efficacy under the operational conditions of urban malaria control programme in Surat city, India. Methods : Larvicides were applied at the recommended dose in selected breeding habitats of Anopheles (An. stephensi), Aedes (Ae. aegypti) and Culex (Cx. quinquefasciatus) and reductions in the densities of III and IV instars were compared with that of untreated matched controls. Results : At the construction sites in cemented tanks/chambers VectoBac produced reduction in the density of III and IV instar larvae of An. stephensi (98–100%) and Ae. aegypti (100%) in the first week of application whereas Bacticide produced 71–100% reduction in An. stephensi and 100% in Ae. aegypti. Re-application of VectoBac on Day 10 caused better control up to Day 20 when compared with Bacticide. In stagnant water pools, VectoBac produced 27.6–85.3% reduction in the larvae of An. subpictus and 18.5–83.8% in those of Cx. quinquefasciatus whereas Bacticide produced 23.3–30.3% and 39–97.2% reduction in An. subpictus and Cx. quinquefasciatus larval densities in the first week post application, respectively. Bacticide application gave better impact on Cx. quinquefasciatus larvae in the second week after re-application as compared to VectoBac. In storm water drains, VectoBac caused respectively 6.2–100% and 6.4–97.6% reduction in An. subpictus and Cx. quinquefasciatus larvae in the first week of application whereas Bacticide produced 100% and 13.3–98.8% reduction in An. subpictus and Cx. quinquefasciatus larval densities, respectively. Interpretation & conclusion : Both the formulations were equally effective on An. subpictus and Cx. quinquefasciatus larvae after a second application. The results showed that application of these biolarvicides would be required at 7–10 day intervals. The health workers engaged in the application of biolarvicides reported a better ease of handling and application of the liquid formulation (VectoBac) than the wettable powder formulation (Bacticide).