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

Abstract

BackgroundDengue 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.MethodsSt. albopicta larval bioassays were carried out to determine the lethal concentrations (LC10, LC50 and LC99) and the resistance ratios (RR10, RR50 and RR99) for temephos. Susceptibility to 4% DDT, 0.05% deltamethrin and 5% malathion was assessed following standard procedure. Knock-down times (KDT10, KDT50 and KDT99) were estimated and knock-down resistance ratios (KRR10, KRR50 and KRR99) were calculated. VectorTest™ dengue antigen assay was used to detect the dengue virus in the field collected mosquitoes.ResultsIn larval bioassays, the RR ranged from 1.4 (for RR99) to 1.7 (for RR50), which suggested that the tested St. albopicta were susceptible to temephos. There was no deviation among the lethal concentration data from linearity (r2 = 0.61). Adult St. albopicta mosquitoes were resistant to DDT, while fully susceptible to deltamethrin and malathion. The knock-down values (KDT10, KDT50 and KDT99) obtained for DDT displayed straight line in log-dose-probit analysis and follow linear regression model. The KRR99 for DDT was 4.9, which indicated a 4.9 folds increase in knock-down resistance to DDT. However, for malathion and deltamethrin, the KRR99 values were 1.6 and 1.5 respectively suggesting that mosquitoes were knock-down sensitive. None of the mosquito pool was dengue virus positive.ConclusionSt. 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.

Multi-insecticide susceptibility evaluation of dengue vectors Stegomyia albopicta and St. aegypti in Assam, India

“…Interestingly the KRR values for St. aegypti were well above 2 among all the test populations which shows evidence that there has been development and spread of knock-down resistance against malathion in the region. Recent studies have reported that dengue vectors are fully susceptible however the KDT 50 in St. albopicta was found to be 3.2 folds higher than the reference [4,16]. Considering the fact that malathion is routinely used in the anti-mosquito fogging operations during the peak epidemic periods of Japanese encephalitis and dengue in northeastern states, the dengue vectors are at continuous selection which might reduce sensitivity to malathion.…”

Self-Limiting OX513A Aedes aegypti Demonstrate Full Susceptibility to Currently Used Insecticidal Chemistries as Compared to Indian Wild-Type Aedes aegypti

“…Both DDT and pyrethroids affect the nervous system by modifying the gating kinetics of voltage-sensitive sodium channels, and mutations in sodium channels can cause binding failures with DDT and pyrethroids, underlying reports of cross-resistance between DDT and pyrethroids [20][21][22][23][24][25]. In this study, the lack of crossresistance to pyrethroids has implicated metabolic resistance as opposed to target-site alterations [16]. For malathion, DEL adult females (98%) were the only strain/sex combination to show survival at this application rate.…”

A Note on the Insecticide Susceptibility Status of Disease Vectors; Anopheles sundaicus and Aedes albopictus, in the Car Nicobar Island

“…In Assam also, Ae. albopictus was susceptible to malathion [18]. Resistance to DDT could have developed due to prolonged use in vector control programmes for over five decades in these islands.…”