First report of L1014F kdr mutation in Culex quinquefasciatus in Mexico

The L1014F mutation in the voltage‐sodium channel gene has been associated with resistance to DDT and pyrethroids in various arthropod species including mosquitoes. We determined the frequency of the L1014F kdr mutation in 16 field populations of Culex quinquefasciatus from Northeastern Mexico collected between 2008 and 2013. The L1014F was present in all populations analyzed with the lowest frequency (3.33%) corresponding to the population from Monclova collected in 2012, and the highest frequency (63.63%) from the Monterrey population collected in 2012. The presence of a kdr mutation in populations of Cx. quinquefasciatus from northeastern Mexico provides evidence of pyrethroid resistance. This requires a special attention, considering that pyrethroid‐based insecticides are commonly used in vector‐control campaigns, especially against Aedes aegypti (L.).     

Evaluation of Insecticides Susceptibility and Malaria Vector Potential of Anopheles annularis s.l. and Anopheles vagus in Assam,India

During the recent past, development of DDT resistance and reduction to pyrethroid susceptibility among the malaria vectors has posed a serious challenge in many Southeast Asian countries including India. Current study presents the insecticide susceptibility and knock-down data of field collected Anopheles annularis sensu lato and An. vagus mosquito species from endemic areas of Assam in northeast India. Anopheles annularis s.l. and An. vagus adult females were collected from four randomly selected sentinel sites in Orang primary health centre (OPHC) and Balipara primary health centre (BPHC) areas, and used for testing susceptibility to DDT, malathion, deltamethrin and lambda-cyhalothrin. After insecticide susceptibility tests, mosquitoes were subjected to VectorTest^™ assay kits to detect the presence of malaria sporozoite in the mosquitoes. An. annularis s.l. was completely susceptible to deltamethrin, lambda-cyhalothrin and malathion in both the study areas. An. vagus was highly susceptible to deltamethrin in both the areas, but exhibited reduced susceptibility to lambda-cyhalothrin in BPHC. Both the species were resistant to DDT and showed very high KDT₅₀ and KDT₉₉ values for DDT. Probit model used to calculate the KDT₅₀ and KDT₉₉ values did not display normal distribution of percent knock-down with time for malathion in both the mosquito species in OPHC (p<0.05) and An. vagus in BPHC (χ² = 25.3; p = 0.0), and also for deltamethrin to An. vagus in BPHC area (χ² = 15.4; p = 0.004). Minimum infection rate (MIR) of Plasmodium sporozoite for An. vagus was 0.56 in OPHC and 0.13 in BPHC, while for An. annularis MIR was found to be 0.22 in OPHC. Resistance management strategies should be identified to delay the expansion of resistance. Testing of field caught Anopheles vectors from different endemic areas for the presence of malaria sporozoite may be useful to ensure their role in malaria transmission.     

Insecticide resistance status of three vectors of Japanese encephalitis in east central India

Japanese encephalitis (JE) has been reported in different districts of Odisha state (east central India) since 1992. During 2016, a major outbreak of JE and acute encephalitis syndrome (AES) occurred in the Malkangiri district of Odisha, causing 103 deaths in children, of which 37 were caused by JE and 66 by AES. Information on insecticide resistance in JE vectors is important for the selection of appropriate insecticides for use in vector control. The present study was designed to determine the resistance status of three important vectors of JE, Culex vishnui, Culex tritaeniorhynchus and Culex bitaeniorhynchus (Diptera: Culicidae), against dichlorodiphenyltrichloroethane (DDT), malathion and deltamethrin in three districts of Odisha state affected by JE. Female adult mosquitoes were collected using mouth aspirators both indoors and outdoors in JE‐affected villages and used in susceptibility bioassays following World Health Organization guidelines. Knock‐downs were recorded every 10 min up to 1 h and mortality rates were recorded at 24 h post‐exposure. Culex vishnui and Cx. tritaeniorhynchus showed resistance to DDT, malathion and deltamethrin, whereas Cx. bitaeniorhynchus was susceptible in all study districts. The information generated by this study will be highly useful in the planning and implementing of appropriate vector control operations for the prevention and control of JE in east central India.     

Changes in malathion and pyrethroid resistance after cypermethrin selection of Culex quinquefasciatus field populations of Cuba

Abstract. Use. of the organophosphorus insecticide malathion for mosquito control in Cuba, for 7 years up to 1986, selected elevated non-specific esterase and altered acetylcholinesterase (AChE) resistance mechanisms in Culex quinquefasciatus. In central Havana space-spraying of malathion was replaced by the pyrethroid cypermethrin in 1987: alternate cycles of malathion and cypermethrin were applied in some of the more rural areas of Havana district during 1987-91. Consequently, populations of Cx quinquefasciatus in the central area of Havana developed resistance to cypermethrin, but there is no evidence of pyrethroid resistance in the outlying areas. Malathion resistance levels declined significantly after 1986, measured both by bioassay and the frequency of the elevated esterase resistance mechanism, and then stabilized with no measurable decline during 1990 in any of the populations tested. These populations had less than 10% frequency of susceptible homozygotes for both the esterase and AChE resistance mechanisms, indicating that organophosphate resistance is still prevalent in Cuban Cx quinquefasciatus. These two mechanisms appear to be in linkage equilibrium, suggesting that current selection for double resistance is not strong. In the central Havana region, pirimiphos-methyl, an organophosphorus insecticide unaffected by the two common malathion resistance mechanisms, is now being used in a resistance management strategy designed to avoid pyrethroid resistance spreading.     

Susceptibility of adult mosquitoes to insecticides in aqueous sucrose baits

Mosquitoes characteristically feed on plant‐derived carbohydrates and honeydew just after emergence and intermittently during their lives. Development of toxic baits focusing on this carbohydrate‐seeking behavior may potentially contribute to localized control. In the present study, ten insecticides were fed to female Culex quinquefasciatus, Anopheles quadrimaculatus, and Aedes taeniorhynchus in a 10% sucrose solution. Active ingredients representative of five classes of insecticides (pyrethroids, phenylpyroles, pyrroles, neonicotinoids, and macrocyclic lactones) were selected for comparison with commercial formulations used to facilitate incorporation of active ingredients into aqueous sucrose solutions. Sucrose as a phagostimulant significantly enhanced mortality to toxicants. In general, the most effective active ingredients were fipronil, deltamethrin and imidacloprid, followed by spinosad, thiamethoxam, bifenthrin, permethrin, and cyfluthrin. The least effective ingredients were chlorfenapyr and ivermectin. For some of the ingredients tested, Cx. quinquefasciatus was the least susceptible species. One‐day‐old male Cx. quinquefasciatus were more susceptible than females; however, no differences existed between one‐ and seven‐day‐old mosquitoes. There were no differences in susceptibility between unfed and gravid ten‐day‐old female Cx. quinquefasciatus to bifenthrin. In conclusion, several pesticides from different classes of compounds have potential for use in development of toxic baits for mosquitoes.     

Behavioural and insecticidal effects of organophosphate‐, carbamate‐ and pyrethroid‐treated mosquito nets against African malaria vectors

Three insecticides – the pyrethroid deltamethrin, the carbamate carbosulfan and the organophosphate chlorpyrifos‐methyl – were tested on mosquito nets in experimental huts to determine their potential for introduction as malaria control measures. Their behavioural effects and efficacy were examined in Anopheles gambiae Giles s.s. (Diptera: Culicidae) and Anopheles funestus Giles s.s. in Muheza, Tanzania, and in Anopheles arabiensis Patton and Culex quinquefasciatus Say in Moshi, Tanzania. A standardized dosage of 25 mg/m² plus high dosages of carbosulfan (50 mg/m², 100 mg/m² and 200 mg/m²) and chlorpyrifos‐methyl (100 mg/m²) were used to compare the three types of insecticide. At 25 mg/m², the rank order of the insecticides for insecticide‐induced mortality in wild An. gambiae and An. funestus was, respectively, carbosulfan (88%, 86%) > deltamethrin (79%, 78%) > chlorpyrifos‐methyl (35%, 53%). The rank order of the insecticides for blood‐feeding inhibition (reduction in the number of blood‐fed mosquitoes compared with control) in wild An. gambiae and An. funestus was deltamethrin > chlorpyrifos‐methyl > carbosulfan. Carbosulfan was particularly toxic to endophilic anophelines at 200 mg/m², killing 100% of An. gambiae and 98% of An. funestus that entered the huts. It was less effective against the more exophilic An. arabiensis (67% mortality) and carbamate‐resistant Cx quinquefasciatus (36% mortality). Carbosulfan deterred anophelines from entering huts, but did not deter carbamate‐resistant Cx quinquefasciatus. Deltamethrin reduced the proportion of insects engaged in blood‐feeding, probably as a consequence of contact irritancy, whereas carbosulfan seemed to provide personal protection through deterred entry or perhaps a spatial repellent action. Any deployment of carbosulfan as an individual treatment on nets should be carried out on a large scale to reduce the risk of diverting mosquitoes to unprotected individuals. Chlorpyrifos‐methyl was inferior to deltamethrin in terms of mortality and blood‐feeding inhibition and would be better deployed on a net in combination with a pyrethroid to control insecticide‐resistant mosquitoes.     

Insecticide susceptibility of Phlebotomus argentipes in visceral leishmaniasis endemic districts in India and Nepal

Objectives

To investigate the DDT and deltamethrin susceptibility of Phlebotomus argentipes, the vector of Leishmania donovani, responsible for visceral leishmaniasis (VL), in two countries (India and Nepal) with different histories of insecticide exposure.

Methods

Standard WHO testing procedures were applied using 4% DDT and 0.05% deltamethrin impregnated papers. The effect of the physiological status (fed and unfed) of females on the outcome of the bioassays was assessed and the optimal time of exposure for deltamethrin was evaluated on a colony population. Field populations from both countries were tested.

Results

Fed and unfed females responded in a similar way. For exposure time on field samples 60 min was adopted for both DDT and deltamethrin. In Bihar, knockdown and mortality with DDT was respectively 20 and 43%. In Nepal almost all sand flies were killed, except at the border with Bihar (mortality 62%). With 0.05% deltamethrin, between 96 and 100% of the sand flies were killed in both regions.

Conclusions

Based on literature and present data 4% DDT and 0.05% deltamethrin seem to be acceptable discriminating concentrations to separate resistant from susceptible populations. Resistance to DDT was confirmed in Bihar and in a border village of Nepal, but the sand flies were still susceptible in villages more inside Nepal where only synthetic pyrethroids are used for indoor spraying. The low effectiveness of indoor spraying with DDT in Bihar to control VL can be partially explained by this resistance hence other classes of insecticides should be tested. In both countries P. argentipes sand flies were susceptible to deltamethrin.     

Behavioral responses of Aedes aegypti,Aedes albopictus,Culex quinquefasciatus,and Anopheles minimus against various synthetic and natural repellent compounds

The behavioral responses of colony populations of Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and Anopheles minimus to four essential oils (citronella, hairy basil, catnip, and vetiver), two standard repellents (DEET and picaridin), and two synthetic pyrethroids (deltamethrin and permethrin) were conducted in the laboratory using an excito‐repellency test system. Results revealed that Cx. quinquefasciatus and An. minimus exhibited much stronger behavioral responses to all test compounds (65–98% escape for contact, 21.4–94.4% escape for non‐contact) compared to Ae. aegypti (3.7–72.2% escape (contact), 0–31.7% (non‐contact)) and Ae. albopictus (3.5–94.4% escape (contact), 11.2–63.7% (non‐contact)). In brief, essential oil from vetiver elicited the greatest irritant responses in Cx. quinquefasciatus (96.6%) and An. minimus (96.5%) compared to the other compounds tested. The synthetic pyrethroids caused a stronger contact irritant response (65–97.8% escape) than non‐contact repellents (0–50.8% escape for non‐contact) across all four mosquito species. Picaridin had the least effect on all mosquito species. Findings from the current study continue to support the screening of essential oils from various plant sources for protective properties against field mosquitoes.     

Frequency of pyrethroid resistance in Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Thailand

Thirty‐two Aedes aegypti populations collected throughout Thailand and five populations of Aedes albopictus from southern Thailand were subjected to standard WHO contact bioassays to assess susceptibility to three commonly used synthetic pyrethroids: permethrin, deltamethrin, and lambda‐cyhalothrin. A wide degree of physiological response to permethrin was detected in Ae. aegypti, ranging from 56.5% survival (Lampang, northern Thailand) to only 4% (Kalasin in northeastern and Phuket in southern Thailand). All 32 populations of Ae. aegypti were found to have evidence of incipient resistance (62.5%) or levels of survival deemed resistant (37.5%) to permethrin. Four populations of Ae. albopictus were found with incipient resistance (97 – 80% mortality) and one with resistance (< 80%) to permethrin. The majority of Ae. aegypti populations (68.7%) was susceptible (> 98% mortality) to deltamethrin, with incipient resistance (observed 97–82% mortality) in other localities. In contrast, all populations of Ae. aegypti were completely susceptible (100% mortality) to the recommended operational dosage of lambda‐cyhalothrin. All five populations of Ae. albopictus were found completely susceptible to both deltamethrin and lambda‐cyhalothrin. Evidence of defined incipient or resistance to synthetic pyrethroids mandates appropriate response and countermeasures to mitigate further development and spread of resistance. In light of these findings, we conclude that routine and comprehensive susceptibility monitoring of dengue mosquito vectors to synthetic pyrethroids should be a required component of resistance management policies and disease control activities.     

Pyrethroid resistance in Anopheles gambiae s.s. and Anopheles arabiensis in western Kenya: phenotypic,metabolic and target site characterizations of three populations

Field and laboratory investigations revealed phenotypic, target site and metabolic resistance to permethrin in an Anopheles gambiae s.s. (Diptera: Culicidae) population in Bungoma District, a region in western Kenya in which malaria is endemic and rates of ownership of insecticide‐treated bednets are high. The sensitivity of individual An. gambiae s.l. females as indicated in assays using World Health Organization (WHO) test kits demonstrated reduced mortality in response to permethrin, deltamethrin and bendiocarb. Estimated time to knock‐down of 50% (KDT₅₀) of the test population in Centers for Disease Control (CDC) bottle bioassays was significantly lengthened for the three insecticides compared with that in a susceptible control strain. Anopheles arabiensis from all three sites showed higher mortality to all three insecticides in the WHO susceptibility assays compared with the CDC bottle assays, in which they showed less sensitivity and longer KDT₅₀ than the reference strain for permethrin and deltamethrin. Microplate assays revealed elevated activity of β‐esterases and oxidases, but not glutathione‐S‐transferase, in An. gambiae s.s. survivors exposed to permethrin in bottle bioassays compared with knocked down and unexposed individuals. No An. arabiensis showed elevated enzyme activity. The 1014S kdr allele was fixed in the Bungoma An. gambiae s.s. population and absent from An. arabiensis, whereas the 1014F kdr allele was absent from all samples of both species. Insecticide resistance could compromise vector control in Bungoma and could spread to other areas as coverage with longlasting insecticide‐treated bednets increases.     

Anopheles arabiensis and An. quadriannulatus resistance to DDT in South Africa

The malaria control programme of KwaZulu‐Natal Province, South Africa, includes Mamfene and Mlambo communities. Western‐type houses there are currently sprayed with deltamethrin, whereas traditional houses are sprayed with DDT for malaria control. In 2002, mosquitoes of the Anopheles gambiae complex (Diptera: Culicidae) were collected from DDT‐sprayed houses, by window exit traps, and from man‐baited nets outdoors. Larval collections were also carried out at Mzinweni Pan near Mlambo. Species of the An. gambiae complex were identified by rDNA polymerase chain reaction assay. The majority of samples collected by window trap and baited nets were identified as the malaria vector An. arabiensis Patton, with a few An. merus Dönitz and An. quadriannulatus (Theobald). The larval collections were predominantly An. quadriannulatus with a small number of An. arabiensis. Standard WHO insecticide susceptibility tests using 4% DDT and 0.05% deltamethrin were performed on both wild‐caught females and laboratory‐reared progeny from wild‐caught females. Wild‐caught An. arabiensis samples from window traps gave 63% and 100% mortality 24‐h post‐exposure to DDT or deltamethrin, respectively. Wild‐caught An. arabiensis samples from man‐baited net traps gave 81% mortality 24‐h post‐exposure to DDT. The F₁ progeny from 22 An. arabiensis females showed average mortality of 86.5% 24‐h post‐exposure to DDT. Less than 80% mortality was recorded from five of these families. Biochemical analyses of samples from each of the families revealed comparatively high levels of glutathione‐S‐transferases and non‐specific esterases in some families, but without significant correlation to bioassay results. Wild‐caught An. quadriannulatus larvae were reared through to adults and assayed on 4% DDT, giving 47% (n = 36) mortality 24‐h post‐exposure. Finding DDT resistance in the vector An. arabiensis, close to the area where we previously reported pyrethroid‐resistance in the vector An. funestus Giles, indicates an urgent need to develop a strategy of insecticide resistance management for the malaria control programmes of southern Africa.     

Differential protein expression in the midgut of Culex quinquefasciatus mosquitoes induced by the insecticide temephos

Mosquitoes are vectors for pathogens of malaria, lymphatic filariasis, dengue, chikungunya, yellow fever and Japanese encephalitis. Culex quinquefasciatus Say, 1823 (Diptera: Culicidae) is a known vector of lymphatic filariasis. Its control in Brazil has been managed using the organophosphate temephos. Studies examining the proteins of Cx. quinquefasciatus that are differentially expressed in response to temephos further understanding of the modes of action of the insecticide and may potentially identify resistance factors in the mosquito. In the present study, a comparative proteomic analysis, using 2‐dimensional electrophoresis coupled with matrix‐assisted laser desorption/ionization (MALDI) time of flight (TOF)/TOF mass spectrometry, and bioinformatics analyses were performed to identify midgut proteins in Cx. quinquefasciatus larvae that were differentially expressed in response to exposure to temephos relative to those in untreated controls. A total of 91 protein spots were differentially expressed; 40 were upregulated and 51 were downregulated by temephos. A total of 22 proteins, predominantly upregulated, were identified as known to play a role in the immune response, whereas the downregulated proteins were involved in energy and protein catabolism. This is the first proteome study of the midgut of Cx. quinquefasciatus and it provides insights into the molecular mechanisms of insecticide‐induced responses in the mosquito.     

Evaluation of collection methods for Culex quinquefasciatus,Aedes aegypti,and Aedes simpsoni in northeastern Tanzania

In East Africa, significant morbidity and mortality are caused by infections spread by Culex quinquefasciatus and Aedes aegypti. Sticky traps have been shown to be effective tools for sampling populations of Aedes mosquitoes and have been found to catch Cx. quinquefasciatus. Thus, they could potentially be used to sample populations of this species. This study compared Sticky ovitraps (SO) and MosquiTraps (MQT) with the CDC Gravid trap (CDC‐GT) for collection of Culex and Aedes mosquito populations in Tanzania. A follow‐up experiment was carried out using traps set for a 24‐h period to accommodate the oviposition habits of Aedes aegypti and Ae. simpsoni s.l. mosquitoes. The results showed that the CDC‐GT caught significantly more Cx. quinquefasciatus and Ae. aegypti than the SO or MQT, but there was no significant difference in the number of mosquitoes caught between the two sticky traps or of Ae. simpsoni s.l. caught among the three trap types. The results suggest that CDC‐GTs are the most appropriate in sampling of Cx. quinquefasciatus. Although CDC‐GTs collected more Ae. aegypti than the sticky traps, the simplicity and cost benefit of sticky traps facilitates large scale studies. All three trap types should be considered for monitoring Aedes mosquitoes.     

不同地理种群尖音库蚊复组抗性动态和遗传多样性

通过生物测定、蛋白质电泳和等位酶分析等方法对5个不同地区的尖音库蚊复组蚊虫Culex pipiens complex的抗性水平、种群中非特异性酯酶基因表型分布和种群遗传多样性进行了研究。不同地理种群的抗性检测结果表明：5个种群分别对敌敌畏、对硫磷、氯菊酯和溴氰菊酯的抗性较高,对残杀威、巴沙和胺菊酯的抗性较低;朝阳种群对敌敌畏抗性最高（55.7倍）,武汉种群次之;佛山种群对氯菊酯和溴氰菊酯的抗性比率高达123倍和23.9倍。酯酶电泳结果显示：5个种群间酯酶多态性存在差异,广州和佛山两个库蚊种群酯酶表型多态性最高,有B1,A2-B2,A8-B8,A9-B9,B10和A11-B11等6种酯酶表型,提示高活性酯酶是主要的抗性机制。群体遗传学研究表明：每位点平均等位基因数（A）为2.76,平均多态位点百分率（P）为64.45％,平均预期杂合度（He）为0.1943,种群间遗传分化系数（Fst）值为0.10,平均基因流(Nm)＝2.57,说明5个种群有较丰富的遗传多样性,种群内遗传多样性高于种群之间。据此推测,种群间可以通过迁徙等方式进行基因交流,使得遗传结构、抗性水平朝一致性方向变化。本研究对我国尖音库蚊复组蚊虫的综合治理有一定指导意义。     

Enzymatic Characterization of Insecticide Resistance Mechanisms in Field Populations of Malaysian Culex quinquefasciatus Say (Diptera: Culicidae)

Background

There has been no comprehensive study on biochemical characterization of insecticide resistance mechanisms in field populations of Malaysian Culex quinquefasciatus. To fill this void in the literature, a nationwide investigation was performed to quantify the enzyme activities, thereby attempting to characterize the potential resistance mechanisms in Cx. quinquefasciatus in residential areas in Malaysia.

Methodology/Principal Findings

Culex quinquefasciatus from 14 residential areas across 13 states and one federal territory were subjected to esterases, mixed function oxidases, glutathione-S-transferase and insensitive acetylcholinesterase assays. Enzyme assays revealed that α-esterases and β-esterases were elevated in 13 populations and 12 populations, respectively. Nine populations demonstrated elevated levels of mixed function oxidases and glutathione-S-transferase. Acetylcholinesterase was insensitive to propoxur in all 14 populations. Activity of α-esterases associated with malathion resistance was found in the present study. In addition, an association between the activity of α-esterases and β-esterases was also demonstrated.

Conclusions/Significance

The present study has characterized the potential biochemical mechanisms in contributing towards insecticide resistance in Cx. quinquefasciatus field populations in Malaysia. Identification of mechanisms underlying the insecticide resistance will be beneficial in developing effective mosquito control programs in Malaysia.     

Characterisation of DDT and pyrethroid resistance in Trinidad and Tobago populations of Aedes aegypti

Insecticide resistance is an important factor in the effectiveness of Aedes aegypti control and the related spread of dengue. The objectives of this study were to investigate the status of the organochlorine dichlorodiphenyltrichloroethane (DDT) and pyrethroid (permethrin and deltamethrin) resistance in Trinidad and Tobago populations of Ae. aegypti and the underlying biochemical mechanisms. Nine populations of Ae. aegypti larvae from Trinidad and Tobago were assayed to DDT and PYs using the Centers for Disease Control and Prevention (CDC) time-mortality-based bioassay method. A diagnostic dosage (DD) was established for each insecticide using the CAREC reference susceptible Ae. aegypti strain and a resistance threshold (RT), time in which 98-100% mortality was observed in the CAREC strain, was calculated for each insecticide. Mosquitoes which survived the DD and RT were considered as resistant, and the resistance status of each population was categorised based on the WHO criteria with mortality <80% indicative of resistance. Biochemical assays were conducted to determine the activities of α and β esterases, mixed function oxidases (MFO) and glutathione-S-transferases (GST) enzymes which are involved in resistance of mosquitoes to DDT and PYs. Enzymatic activity levels in each population were compared with those obtained for the CAREC susceptible strain, and significant differences were determined by Kruskal-Wallis and Tukey's non-parametric tests (P<0.05). The established DDs were 0.01 mg l(-1), 0.2 mg l(-1) and 1.0 mg l(-1) for deltamethrin, permethrin and DDT, respectively; and the RTs for deltamethrin, permethrin and DDT were 30, 75 and 120 min, respectively. All Ae. aegypti populations were resistant to DDT (<80% mortality); two strains were incipiently resistant to deltamethrin and three to permethrin (80-98% mortality). Biochemical assays revealed elevated levels of α-esterase and MFO enzymes in all Ae. aegypti populations. All, except three populations, showed increased levels of β-esterases; and all populations, except Curepe, demonstrated elevated GST levels.Metabolic detoxification of enzymes is correlated with the manifestation of DDT and PY resistance in Trinidad and Tobago populations of Ae. aegypti. The presence of this resistance also suggests that knock down (kdr)-type resistance may be involved, hence the need for further investigations. This information can contribute to the development of an insecticide resistance surveillance programme and improvement of resistance management strategies aimed at combatting the spread of dengue in Trinidad and Tobago.     

Insecticide susceptibility status and major detoxifying enzymes activity in Anopheles subpictus from Kasur,Pakistan

Anopheles subpictus s.l. Grassi (Diptera: Culicidae) is a malaria vector in South Asia, where insecticides are the mainstay for vector control interventions. Information on any variation in metabolic enzyme levels in mosquitoes is helpful with respect to adapting alternative strategies for vector control. The scarce data on the biochemical basis of insecticide resistance in malaria vectors of Pakistan limit the available information for vector control interventions within the country. The insecticide susceptibility status and its biochemical basis against dichlorodiphenyltrichloroethane (DDT) (4%), deltamethrin (0.05%) and permethrin (0.75%) in An. subpictus s.l. collected from all Tehsils of district Kasur were evaluated. For this purpose, a World Health Organization susceptibility bioassay was performed followed by the detection of altered metabolic enzyme activity using biochemical assays. Similarly, a significant difference in knock‐down effect was observed among field collected and susceptible strain against all insecticides 24 h post exposure. The overall mean mortality rates of DDT, deltamethrin and permethrin were 27.86% [95% confidence interval (CI) = 29.65–26.06], 44.89% (95% CI = 46.23–43.54) and 78.82% (95% CI = 80.16–77.47), respectively. The biochemical assays revealed an elevated level of metabolic enzymes in the field population. The results provide evidence of resistance against organochlorine and pyrethroid groups in a field population of An. subpictus s.l. from district Kasur mediated by multiple metabolic mechanisms, including acetylcholinesterases, esterases, cytochrome P450 and glutathione S‐transferases.     

新疆棉铃虫对溴氰菊酯和硫丹 抗性的生化机理研究

通过生物测定和生化分析研究了新疆棉铃虫Helicoverpa armigera (Hübner)敏感种群和室内筛选获得的抗性种群对硫丹和溴氰菊酯的反应及其α-乙酸萘酯酶和乙酰胆碱酯酶的动态活性反应。结果表明,筛选后新疆棉铃虫对硫丹和溴氰菊酯产生的抗性倍数分别为13倍和66倍。两个抗性种群的α-乙酸萘酯酶和乙酰胆碱酯酶比活力均高于敏感种群。相应杀虫剂预处理后,α-乙酸萘酯酶酶活力受到抑制。抗性种群的α-乙酸萘酯酶对底物的亲和力高于敏感种群,但Vmax低于敏感种群。抗性种群的乙酰胆碱酯酶对底物的亲和力显著低于敏感种群,Vmax比敏感种群高。聚丙烯酰胺凝胶电泳显示,两个抗性种群都有一条特异性酶带,其迁移率相近,且均可被甲基对氧磷抑制。因此推测,α-乙酸萘酯酶参与了新疆棉铃虫对硫丹和溴氰菊酯的抗性,具有代谢和阻断作用;乙酰胆碱酯酶对抗性的产生也起到了重要作用。     

Glutathione S-transferase detoxification as a potential pyrethroid resistance mechanism in the maize weevil, Sitophilus zeamais

Insecticide resistance patterns among 16 Brazilian populations of the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), were recognized by surveying resistance to three organophosphates (chlorpyrifos‐methyl, malathion, and pirimiphos‐methyl) and three pyrethroids (cypermethrin, deltamethrin, and permethrin). Two population clusters were obtained: one with three populations (Bragança Paulista, Cristalina, and Nova Andradina) showing low frequency of cypermethrin resistance (13–36%) and negligible frequency of deltamethrin resistance (2–9%); and another with six populations (Campos dos Goytacazes, Ivinhema, Patos de Minas, Penápolis, Uberlândia, and Venda Nova) showing low to negligible levels of pyrethroid resistance (0–23%). The remaining seven populations, including a susceptible, and a DDT‐ and pyrethroid‐resistant reference populations (Sete Lagoas and Jacarezinho, respectively), were significantly different from each other and from the two recognized clusters. In contrast with pyrethroid resistance, organophosphate resistance was negligible except for chlorpyrifos‐methyl in two populations (Fátima do Sul and Penápolis). There was no correlation between geographic distance and the Mahalanobis distance estimated from the resistance pattern ordination of the populations by canonical variate analysis, suggesting local selection and/or broad dispersal of resistant populations by grain trade. The results of biochemical in vitro studies measuring the activity of detoxification enzymes (esterases and glutathion S‐transferases) in conjunction with canonical correlation analysis suggest a major involvement of enhanced conjugation by glutathione S‐transferases (> 2‐fold increase) in pyrethroid resistance and, in the case of cypermethrin resistance, enhanced phosphotriesterase activity.     

Gene expression profiles of the Southern house mosquito Culex quinquefasciatus during exposure to permethrin

Insecticide resistance is a major obstacle to the management of disease‐vectoring mosquitoes worldwide. The genetic changes and detoxification genes involved in insecticide resistance have been extensively studied in populations of insecticide‐resistant mosquitoes, however few studies have focused on the resistance genes upregulated upon insecticide exposure and the possible regulation pathways involved in insecticide resistance. To characterize the changes in gene expression during insecticide exposure, and to investigate the possible connection of known regulation pathways with insecticide resistance, we conducted RNA‐Seq analysis of a highly permethrin‐resistant strain of Culex quinquefasciatus following permethrin exposure. Gene expression profiles revealed a total of 224 upregulated and 146 downregulated genes when compared to a blank acetone carrier treated control, respectively, suggesting that there were multiple, but specific genes involved in permethrin resistance. Functional enrichment analysis showed that the upregulated genes contained multiple detoxification genes including a glutathione S‐transferase and multiple cytochrome P450 genes, as well as several immune‐related genes, while the downregulated genes consisted primarily of proteases and carbohydrate metabolism and transport. Further analysis showed that permethrin exposure resulted in a decrease in the expression of serum storage proteins and likely represented a delay in the development of the fourth instar possibly due to a decrease in feeding. This effect was more pronounced in an insecticide‐resistant strain than in an insecticide‐susceptible strain and may represent a behavioral mechanism of insecticide resistance in Culex mosquitoes.