Insecticide susceptibility and dengue vector status of wild Stegomyia albopicta in a strategically important area of Assam, India

Abstract

Background

Dengue vector control programmes are facing operational challenges due to resistance against commonly used insecticides throughout the endemic countries. Recently, there has been appreciable increase in the dengue cases in India, however, no recent data are available on susceptible status of dengue vectors. We have studied the susceptibility level of St. albopicta to commonly used insecticides in India. Adult mosquitoes were tested for the presence of dengue virus.

Methods

St. albopicta larval bioassays were carried out to determine the lethal concentrations (LC ₁₀, LC ₅₀ and LC ₉₉) and the resistance ratios (RR ₁₀, RR ₅₀ and RR ₉₉) for temephos. Susceptibility to 4% DDT, 0.05% deltamethrin and 5% malathion was assessed following standard procedure. Knock-down times (KDT ₁₀, KDT ₅₀ and KDT ₉₉) were estimated and knock-down resistance ratios (KRR ₁₀, KRR ₅₀ and KRR ₉₉) were calculated. VectorTest™ dengue antigen assay was used to detect the dengue virus in the field collected mosquitoes.

Results

In larval bioassays, the RR ranged from 1.4 (for RR ₉₉) to 1.7 (for RR ₅₀), which suggested that the tested St. albopicta were susceptible to temephos. There was no deviation among the lethal concentration data from linearity (r ² = 0.61). Adult St. albopicta mosquitoes were resistant to DDT, while fully susceptible to deltamethrin and malathion. The knock-down values (KDT ₁₀, KDT ₅₀ and KDT ₉₉) obtained for DDT displayed straight line in log-dose-probit analysis and follow linear regression model. The KRR ₉₉ for DDT was 4.9, which indicated a 4.9 folds increase in knock-down resistance to DDT. However, for malathion and deltamethrin, the KRR ₉₉ values were 1.6 and 1.5 respectively suggesting that mosquitoes were knock-down sensitive. None of the mosquito pool was dengue virus positive.

Conclusion

St. albopicta showed resistance to DDT and reduced sensitivity to deltamethrin and malathion. This data on insecticide resistance could help public health authorities in India to design more effective vector control measures. More dengue vector specimens need to be scanned to identify the potential dengue vector.