Assessment of sublethal effects of permethrin on adult life characteristics and resistance dynamics in Aedes albopictus (Diptera: Culicidae).

Mosquitoes are regularly exposed to adverse effects of insecticides employed in field during vector control campaigns. Its primary goal is to eliminate the vector population; nevertheless, this practise typically ignores the residual impacts and long-term repercussions on the remaining population. Here, the current study analysed how sublethal exposure of insecticides alter the life qualities, genotypic and biochemical characteristics of mosquitoes. The resistance ratio value in Laboratory Resistant (Lab-R) larvae increased 10 times (0.010 mg/l to 0.108 mg/l) compared to Laboratory Susceptible (LabS) larvae. It also revealed that the surviving mosquitoes had 50% reduction in hatchability but had longer larval and pupal periods (15 days and 2 days), respectively. The survival rates decrease in female by 2 days but increase in male by 7 days which is of concern and necessitates additional study. Moreover, major role of monooxygenase was confirmed behind resistance development which was further supported by piperonyl butoxide assay where reduction in Tolerance Ratio (TR50) by 12-fold occurred and gene expression profile also showed high expression level of CYP6P12 gene. In resistant strain, cuticular thickness increased by 1.23 times and alteration at codon 1532 (ATC to TTC) on VGSC gene leads to mutation I1532F. The data gleaned from our work highlights the threat of sublethal insecticides on vector control techniques and offers ample evidence that the larval selection alters adult life qualities, metabolic properties and transgenerational features which contributes to the damage caused by resistance.

Effects of deltamethrin exposure on the cytochrome P450 monooxygenases of Aedes albopictus (Skuse) larvae from a dengue-endemic region of northern part of West Bengal, India.

Aedes albopictus is highly prevalent in the northern part of West Bengal and is considered to be responsible for the recent dengue outbreaks in this region. Control of this vector is largely relied on the use of synthetic pyrethroids, which can lead to the development of resistance. In the present study, larvae of three wild Ae. albopictus populations from the dengue-endemic regions were screened for deltamethrin resistance, and the role of cytochrome P450 monooxygenases (CYPs) was investigated in deltamethrin exposed and unexposed larvae. Two populations were incipient resistant, and one population was completely resistant against deltamethrin. Monooxygenase titration assay revealed the involvement of CYPs in deltamethrin resistance along with an induction effect of deltamethrin exposure. Gene expression studies revealed differential expression of five CYP6 family genes, CYP6A8, CYP6P12, CYP6A14, CYP6N3 and CYP6N6, with high constitutive expression of CYP6A8 and CYP6P12 in all the populations before and after deltamethrin exposure. From these findings, it was evident that CYPs play an important role in the development of deltamethrin resistance in the Ae. albopictus populations in this region.

First report of F1534C kdr mutation in deltamethrin resistant Aedes albopictus from northern part of West Bengal, India.

Dengue is the most rapidly spreading vector-borne disease with an estimated 100-400 million cases each year. Control of Dengue vectors largely depends upon synthetic pyrethroids. Development of insecticide resistance in Aedes mosquitoes however, poses severe threat to insecticide-based vector management programme. Mutations in the Voltage Gated Sodium Channel gene (vgsc) serve as the primary machinery behind this resistance development. In Aedes albopictus, at least four such kdr (knock down resistance) mutations had already been documented. Here, we describe the occurrence of F1534C kdr mutation in wild population of Ae. albopictus from northern part of West Bengal, India including a novel T1520I mutation. Four populations of Ae. albopictus from the studied region were found resistant against DDT and synthetic pyrethroids, among them only one population possessed F1534C kdr mutation. A total of 200 successful amplification followed by partial sequencing of vgsc gene further revealed the presence of F1534C kdr mutation in both phenotypically susceptible and resistant mosquito specimen. Studied populations were found 81% homozygote susceptible (1534F/F), 12.5% heterozygote (1534F/C) and 6% homozygote resistant (1534C/C) for F1534C kdr mutation. The findings of the current study will help to uncover the mechanisms underlying insecticide resistance and hence to reduce errors in vector control measurements.

Occurrence of L1014F and L1014S mutations in insecticide resistant Culex quinquefasciatus from filariasis endemic districts of West Bengal, India.

INTRODUCTION: Lymphatic filariasis causes long term morbidity and hampers the socio-economic status. Apart from the available treatments and medication, control of vector population Culex quinquefasciatus Say through the use of chemical insecticides is a widely applied strategy. However, the unrestrained application of these insecticides over many decades has led to resistance development in the vectors. METHODS: In order to determine the insecticide susceptibility/resistance status of Cx. quinquefasciatus from two filariasis endemic districts of West Bengal, India, wild mosquito populations were collected and assayed against six different insecticides and presence of L1014F; L1014S kdr mutations in the voltage-gated sodium channel gene was also screened along with the use of synergists to evaluate the role of major detoxifying enzymes in resistance development. RESULTS: The collected mosquito populations showed severe resistance to insecticides and the two synergists used-PBO (piperonyl butoxide) and TPP (triphenyl phosphate), were unable to restore the susceptibility status of the vector thereupon pointing towards a minor role of metabolic enzymes. kdr mutations were present in the studied populations in varying percent with higher L1014F frequency indicating its association with the observed resistance to pyrethroids and DDT. This study reports L1014S mutation in Cx. quinquefasciatus for the first time.

Insecticide resistance mapping in the vector of lymphatic filariasis, Culex quinquefasciatus Say from northern region of West Bengal, India.

Culex quinquefasciatus is a vector of lymphatic filariasis and vector control strategies normally involve the use of synthetic insecticides targeted against them. Extensive and uncontrolled use of these synthetic insecticides has led to the development of insecticide resistance in the mosquito vectors. In this context, to study the resistance status of Cx. quinquefasciatus, field populations were collected from three districts of Northern part of West Bengal and tested against insecticides (5% malathion, 0.05% deltamethrin, 0.05% lambdacyhalothrin,0.75% permethrin, 0.1% propoxur, 4% DDT and Temephos). Qualitative and quantitative enzyme assay was also conducted in order to find the role of detoxifying enzymes behind the development of insecticide resistance. This study revealed the presence of widespread resistance amongst the field populations of Cx. quinquefasciatus throughout the studied regions. Moreover, the result of native PAGE and biochemical enzyme assay may be linked to some extent in the involvement of the detoxifying enzymes in conferring resistance against insecticides in most of the tested Cx. quinquefasciatus populations. The present study involving the survey of resistance status may be of immense help during the implementation of vector control strategies throughout this region.

Insecticide resistance in Aedes albopictus Skuse from sub-Himalayan districts of West Bengal, India.

Dengue is one of the most rapidly spreading infectious diseases prevalent throughout the tropical and sub-tropical regions of the world. In absence of specific medications and vaccines, the sole method of disease prevention relies on vector control mainly using insecticides. But with the advent of Insecticide resistance, worldwide vector control programs are facing failure. In this study, eleven different Ae. albopictus population from sub-Himalayan districts of West Bengal, India were investigated as per WHO protocols to find out the current status of insecticide susceptibility against DDT, permethrin and propoxur. Also the role of three insecticide detoxifying enzymes underlying observed resistance was investigated through quantitative and synergistic assays to unveil the mechanism of insecticide resistance. It was found that majority of studied populations were resistant to 4% DDT. Two populations, namely Alipurduar (APD) and Jalpaiguri (JPG) were severely resistant to 0.75% permethrin, whereas only JPG population was found to exhibit severe resistance against 0.1% propoxur. Moreover, the involvement of detoxifying enzymes was also noted in conferring resistance against DDT and Permethrin. This study indicates the inefficacy of DDT in controlling Ae. albopictus populations in the study region. This study may help in implementation of an efficient vector control and insecticide resistance management strategies.

Multiple insecticide resistance mechanisms in primary dengue vector, Aedes aegypti (Linn.) from dengue endemic districts of sub-Himalayan West Bengal, India.

BACKGROUND: Mosquitoes belonging to genus Aedes are the prime vectors of several arboviral diseases such as Dengue, Zika and Chikungunya worldwide. Every year numerous cases of dengue infections occur throughout the world, proper control of which depends on efficient vector control. However the onset of insecticide resistance has resulted in failure of vector control approaches. PRINCIPAL FINDINGS: This study was carried out to unveil the degree of prevailing insecticide resistance along with its underlying mechanisms among the primary dengue vector in dengue endemic districts of West Bengal, India through standard WHO protocol. It was observed that, the majority of the tested populations were found to possess resistance to more than one insecticide. In adult bioassay, the toxicity levels of the six tested insecticides was found to decrease in the following order: deltamethrin > lambdacyhalothrin > malathion > propoxur > permethrin > DDT. In larval bioassay, one of the tested populations was found to possess moderate resistance against temephos, mortality percentage 92.5% and 79.8% for WHO (0.0200 ppm) and National Vector Borne disease Programme, India recommended dose (0.0125 ppm) respectively. Carboxylesterases were found to be involved in conferring resistance as revealed in synergistic and quantitative assay against temephos in North Dinajpur (NDP) population and malathion in Alipurduar (APD) and Darjeeling (DAR) populations. Similar correlations were also observed in the majority of the tested populations between reduced susceptibilities against pyrethroid insecticides and Cytochrome P450s activity. CONCLUSION: Efficient disease management in this region can only be achieved through proper integrated vector management along with tools to minimize insecticide resistance. This study may help the concerned authorities in the formulation of an effective vector control strategy throughout this region incorporating the knowledge gained through this study.

Assessment of insecticide resistance in primary dengue vector, Aedes aegypti (Linn.) from Northern Districts of West Bengal, India.

Aedes mosquitoes are the major vectors transmitting several arboviral diseases such as dengue, zika and chikungunya worldwide. Northern districts of West Bengal is home to several epidemics vectored by mosquito including dengue infections, proper control of which depends on efficient vector control. However the onset of insecticide resistance has resulted in failure of vector control approaches. This study was carried out to unveil the level of insecticide resistance prevailing among the primary dengue vector in this dengue endemic region of India. It was observed that, field caught populations of Ae. aegypti were moderately to severely resistant to majority of the insecticide classes tested, i.e. Organochlorine (DDT), Organophosphates (temephos, malathion), Synthetic Pyrethroids (deltamethrin, lambdacyhalothrin and permethrin) and carbamate (propoxur). In majority of the populations, metabolic detoxification seemed to play the underlying role behind the development of insecticide resistance. This study seems to be the first report revealing the pattern of insecticide resistance in Ae. aegypti from Northern West Bengal. Efficient disease management in this region can only be achieved through proper insecticide resistance management. This study may help the concerned authorities in the formulation of an effective vector control strategy throughout this region incorporating the knowledge gained through this study.

Insecticide susceptibility status and major detoxifying enzymes' activity in Aedes albopictus (Skuse), vector of dengue and chikungunya in Northern part of West Bengal, India.

Mosquitoes belonging to Aedes genus, Aedes aegypti and Aedes albopictus transmit many globally important arboviruses including Dengue (DENV) and Chikungunya (CHIKV). Vector control with the use of insecticide remains the suitable method of choice to stop the transmission of these diseases. However, vector control throughout the world is failing to achieve its target results because of the worldwide development of insecticide resistance in mosquitoes. To assess the insecticide susceptibility status of Aedes albopictus from northern part of West Bengal, the susceptibility of eight different Aedes albopictus populations were tested against a commonly used larvicide (temephos) and some adulticides (malathion, deltamethrin and lambda cyhalothrin) along with the major insecticide detoxifying enzymes' activity in them. Through this study, it was revealed that most of the populations were found susceptible to temephos except Nagrakata (NGK) and Siliguri (SLG), which showed both a higher resistance ratio (RR99) and a lower susceptibility, thereby reflecting the development of resistance against temephos in them. However, all tested adulticides caused 100% mortality in all the population implying their potency in control of this mosquito in this region of India. Through the study of carboxylesterase activity, it was revealed that the NGK population showed a 9.6 fold higher level of activity than susceptible population. The same population also showed a lower level of susceptibility and a higher resistance ratio (RR99), indicating a clear correlation between susceptibility to temephos and carboxylesterase enzymes' activity in this population. This preliminary data reflects that the NGK population is showing a trend towards resistance development and with time, there is possibility that this resistance phenomenon will spread to other populations. With the recurrence of dengue and chikungunya, this data on insecticide susceptibility status of Aedes albopictus could help the authorities engaged in vector control programmes to formulate effective measures against this mosquito in this region.