Insecticide Resistance Monitoring Research Articles

DIFFERENTIAL TOXICITY OF PYRETHROID AND ORGANOPHOSPHATE INSECTICIDES TO THE HONEY BEE, APIS MELLIFERA AND THE YELLOW FEVER MOSQUITO, AEDES AEGYPTI

Six insecticide active ingredients (AIs) and five commercial insecticide formulations were applied by topical application and onto filter paper strips to determine differential toxicity to Aedes aegypti (L.) and Apis mellifera (L.), and to evaluate their potential use in future insecticide resistance monitoring surveys. For topical application, 0.1 or 1 µl of the technical insecticide solution was applied to the Ae. aegypti and A. mellifera thorax, respectively. For insecticide-impregnated strips the insecticide amount varied, according with the commercial formulation. By topical application deltamethrin was the most toxic AI (LD 50 = 0.057 µg/g) to Ae. aegypti and prallethrin was least toxic (LD 50 = 19.42 µg/g). For A. mellifera, the most toxic AIs were deltamethrin (LD 50 = 0.013 µg/g) and bifenthrin (LD50 = 0.156 µg/g); and the least toxic was chlorpyrifos (LD 50 = 3.246 µg/g). When the insecticide-impregnated papers method was used, Mosquitomist Two (chlorpyrifos 24.6%) was the most toxic insecticide for Ae. aegypti (LC50 = 0.024 µg/cm2 ), and Aqualuer (permethrin 20.6%, PBO 20.6%) was least toxic (LC50 = 0.408 µg/cm2 ). For A. mellifera the most toxic commercial insecticide formulations were Talstar (bifenthrin 7.9%; LC50 = 0.288 µg/cm2 ) and Mosquitomist Two (LC50 = 0.299 µg/cm2 ), with no significant differences, and the least toxic commercial formulation was Deltagard (deltamethrin 2.0%; LC50 = 15.084 µg/cm2 ). By topical application, more than 28 times of chlorpyrifos was needed to obtain the same mortality in A. mellifera as in Ae. aegypti. When using the insecticide-impregnated paper method, more than 206 times of Deltagard was needed to obtain the same mortality in A. mellifera as in Ae. aegypti. Even though Mosquitomist Two was the most toxic insecticide for both insect species, the honey bees were >12 times more tolerant to this insecticide, compared with the mosquitoes.

Management of insecticides for use in disease vector control: a global survey

BackgroundVector control plays a critical role in the prevention, control and elimination of vector-borne diseases, and interventions of vector control continue to depend largely on the action of chemical insecticides. A global survey was conducted on the management practices of vector control insecticides at country level to identify gaps to inform future strategies on pesticide management, seeking to improve efficacy of interventions and reduce the side-effects of chemicals used on health and the environment.MethodsA survey by questionnaire on the management practices of vector control insecticides was disseminated among all WHO Member States. Data were analysed using descriptive statistics in MS Excel.ResultsResponses were received from 94 countries, or a 48% response rate. Capacity for insecticide resistance monitoring was established in 68–80% of the countries in most regions, often with external support; however, this capacity was largely lacking from the European & Others Region (i.e. Western & Eastern Europe, North America, Australia and New Zealand). Procurement of vector control insecticides was in 50–75% of countries taking place by agencies other than the central-level procuring agency, over which the central authorities lacked control, for example, to select the product or assure its quality, highlighting the importance of post-market monitoring. Moreover, some countries experienced problems with estimating the correct amounts for procurement, especially for emergency purposes. Large fractions (29–78%) of countries across regions showed shortcomings in worker safety, pesticide storage practices and pesticide waste disposal. Shortcomings were most pronounced in countries of the European & Others Region, which has long been relatively free from mosquito-borne diseases but has recently faced challenges of re-emerging vector-borne diseases.ConclusionsCritical shortcomings in the management of vector control insecticides are common in countries across regions, with risks of adverse pesticide effects on health and the environment. Advocacy and resource mobilization are needed at regional and country levels to address these challenges.

Geographic Monitoring of Insecticide Resistance Mutations in Native and Invasive Populations of the Fall Armyworm.

Simple SummaryThe moth fall armyworm (Spodoptera frugiperda) is a major agricultural pest insect damaging a wide range of crops, especially corn. Field evolved resistance against Bacillus thuringiensis (Bt) toxins and synthetic insecticides has been repeatedly reported. While the fall armyworm is native to the Americas, its biological invasion was first reported from West Africa in 2016. Since then, this pest has been detected across sub-Saharan and North Africa, Asia, and Oceania. Here, we examine the geographical distribution of mutations causing resistance against Bt or synthetic insecticides to test if the invasion was accompanied by the spread of resistance mutations using 177 individuals collected from 12 geographic populations including North and South America, West and East Africa, India, and China. We observed that Bt resistance mutations generated in Puerto Rico or Brazil were found only from their native populations, while invasive populations had higher copy numbers of cytochrome P450 genes and higher proportions of resistance mutations at AChE, which are known to cause resistance against synthetic insecticides. This result explains the susceptibility to Bt insecticides and the resistance against synthetic insecticides in invasive Chinese populations. This information will be helpful in investigating the cause and consequence associated with insecticide resistance.Field evolved resistance to insecticides is one of the main challenges in pest control. The fall armyworm (FAW) is a lepidopteran pest species causing severe crop losses, especially corn. While native to the Americas, the presence of FAW was confirmed in West Africa in 2016. Since then, the FAW has been detected in over 70 countries covering sub-Saharan Africa, the Middle East, North Africa, South Asia, Southeast Asia, and Oceania. In this study, we tested whether this invasion was accompanied by the spread of resistance mutations from native to invasive areas. We observed that mutations causing Bt resistance at ABCC2 genes were observed only in native populations where the mutations were initially reported. Invasive populations were found to have higher gene numbers of cytochrome P450 genes than native populations and a higher proportion of multiple resistance mutations at acetylcholinesterase genes, supporting strong selective pressure for resistance against synthetic insecticides. This result explains the susceptibility to Bt insecticides and resistance to various synthetic insecticides in Chinese populations. These results highlight the necessity of regular and standardized monitoring of insecticide resistance in invasive populations using both genomic approaches and bioassay experiments.

A survey of insecticide resistance-conferring mutations in multiple targets in Anopheles sinensis populations across Sichuan, China

BackgroundSichuan province is located in the southwest of China, and was previously a malaria-endemic region. Although no indigenous malaria case has been reported since 2011, the number of imported cases is on the rise. Insecticide-based vector control has played a central role in the prevention of malaria epidemics. However, the efficacy of this strategy is gravely challenged by the development of insecticide resistance. Regular monitoring of insecticide resistance is essential to inform evidence-based vector control. Unfortunately, almost no information is currently available on the status of insecticide resistance and associated mechanisms in Anopheles sinensis, the dominant malaria vector in Sichuan. In this study, efforts were invested in detecting the presence and frequency of insecticide resistance-associated mutations in three genes that encode target proteins of several classes of commonly used insecticides.MethodsA total of 446 adults of An. sinensis, collected from 12 locations across Sichuan province of China, were inspected for resistance-conferring mutations in three genes that respectively encode acetylcholinesterase (AChE), voltage-gated sodium channel (VGSC), and GABA receptor (RDL) by DNA Sanger sequencing.ResultsThe G119S mutation in AChE was detected at high frequencies (0.40–0.73). The predominant ace-1 genotype was GGC/AGC (119GS) heterozygotes. Diverse variations at codon 1014 were found in VGSC, leading to three different amino acid substitutions (L1014F/C/S). The 1014F was the predominant resistance allele and was distributed in all 12 populations at varying frequencies from 0.03 to 0.86. The A296S mutation in RDL was frequently present in Sichuan, with 296SS accounting for more than 80% of individuals in six of the 12 populations. Notably, in samples collected from Chengdu (DJY) and Deyang (DYMZ), almost 30% of individuals were found to be resistant homozygotes for all three targets.ConclusionsResistance-related mutations in three target proteins of the four main classes of insecticides were prevalent in most populations. This survey reveals a worrisome situation of multiple resistance genotypes in Sichuan malaria vector. The data strengthen the need for regular monitoring of insecticide resistance and establishing a region-customized vector intervention strategy.Graphical abstract

Insecticide Resistance Monitoring of the Diamondback Moth (Lepidoptera: Plutellidae) Populations in China.

The diamondback moth, Plutella xylostella L., is a worldwide crop pest that is difficult to control because of its ability to develop resistance to many insecticides. To provide a reference for resistance management of P. xylostella in China, the present study used a leaf-dip bioassay to monitor the resistance of P. xylostella to nine insecticides in eight regions of China. The results showed that P. xylostella had developed a high level of resistance to beta-cypermethrin (resistance ratio [RR] > 112), and moderate (RR < 40) to high levels of resistance to indoxacarb, abamectin, and chlorfluazuron. For chlorantraniliprole, RRs > 100 were found in Midu (Yunnan Province) and Jinghai (Tianjin). In most regions, the resistance to spinetoram and chlorfenapyr and Bacillus thuringiensis (Bt) was low. No resistance was detected to diafenthiuron. Overall, P. xylostella resistance to insecticides was higher in Midu than in other regions. The data in this study should help guide the selection of insecticides for management of P. xylostella in China.

Insecticide resistance and genetic structure of Aedes aegypti populations from Rio de Janeiro State, Brazil.

Vector control largely relies on neurotoxic chemicals, and insecticide resistance (IR) directly threatens their effectiveness. In some cases, specific alleles cause IR, and knowledge of the genetic diversity and gene flow among mosquito populations is crucial to track their arrival, rise, and spread. Here we evaluated Aedes aegypti populations’ susceptibility status, collected in 2016 from six different municipalities of Rio de Janeiro state (RJ), to temephos, pyriproxyfen, malathion, and deltamethrin. We collected eggs of Ae. aegypti in Campos dos Goytacazes (Cgy), Itaperuna (Ipn), Iguaba Grande (Igg), Itaboraí (Ibr), Mangaratiba (Mgr), and Vassouras (Vsr). We followed the World Health Organization (WHO) guidelines and investigated the degree of susceptibility/resistance of mosquitoes to these insecticides. We used the Rockefeller strain as a susceptible positive control. We genotyped the V1016I and F1534C knockdown resistance (kdr) alleles using qPCR TaqMan SNP genotyping assay. Besides, with the use of Ae. aegypti SNP-chip, we performed genomic population analyses by genotyping more than 15,000 biallelic SNPs in mosquitoes from each population. We added previous data from populations from other countries to evaluate the ancestry of RJ populations.All RJ Ae. aegypti populations were susceptible to pyriproxyfen and malathion and highly resistant to deltamethrin. The resistance ratios for temephos was below 3,0 in Cgy, Ibr, and Igg populations, representing the lowest rates since IR monitoring started in this Brazilian region. We found the kdr alleles in high frequencies in all populations, partially justifying the observed resistance to pyrethroid. Population genetics analysis showed that Ae. aegypti revealed potential higher migration among some RJ localities and low genetic structure for most of them. Future population genetic studies, together with IR data in Ae aegypti on a broader scale, can help us predict the gene flow within and among the Brazilian States, allowing us to track the dynamics of arrival and changes in the frequency of IR alleles, and providing critical information to improving vector control program.

Insecticide resistance monitoring for the invasive populations of fall armyworm, Spodoptera frugiperda in China

Fall armyworm has invaded China and colonized its populations in tropical and sub-tropical regions of South China since December 2018. Chemical spray has been widely used to control the pest, which shall lead to resistance evolution. In this research, we collected five populations of the pest from Yunnan, Hainan, Tibet, and Fujian of China, and tested their susceptibilities to pyrethroid, organophosphorus, oxadiazine, diamide, antibiotics and other types of insecticides (14 insecticides totally) in the laboratory. Based on the susceptible baseline published from the previous studies, the resistance ratio was 615–1 068-fold to chlorpyrifos, 60–388-fold to spinosad, 26–317-fold to lambda-cyhalothrin, 13–29-fold to malathion, 9–33-fold to fenvalerate, 8–20-fold to deltamethrin, 3–8-fold to emamectin benzoate and 1–2-fold to chlorantraniliprole, respectively. The median lethal concentration (LC50) of other six insecticides without the susceptible baselines was 148.27–220.96 μg mL−1 for beta-cypermethrin, 87.03–128.43 μg mL−1 for chlorfenapyr, 16.35–99.67 μg mL−1 for indoxacarb, 10.55–51.01 μg mL−1 for phoxim, 7.08–8.78 μg mL−1 for M-EBI (the mixed insecticide of emamectin benzoate and indoxcarb) and 1.49–4.64 μg mL−1 for cyantraniliprole. This study can be helpful for chemical control as well as for resistance monitoring and management of the pest in China.

Laboratory Selection, Cross-Resistance, Risk Assessment to Lambda-Cyhalothrin Resistance, and Monitoring of Insecticide Resistance for Plant Bug Lygus pratensis (Hemiptera: Miridae) in Farming-Pastoral Ecotones of Northern China.

The plant bug Lygus pratensis Linnaeus (Hemiptera: Miridae) is an important insect pest of alfalfa in grassland farming in northern China. A field population of L. pratensis was selected in the laboratory for 14 consecutive generations with lambda-cyhalothrin to generate 42.555-fold resistance. Selection also induced low cross-resistance to imidacloprid and beta-cypermethrin, and medium cross-resistance to deltamethrin. Realized heritability (h2) of lambda-cyhalothrin resistance was 0.339. Susceptible baselines of L. pratensis were established for five insecticides using the glass-vial method, the values of which were 6.849, 3.423, 8.778, 3.559, and 117.553 ng/cm2 for phoxim, methomyl, imidacloprid, lambda-cyhalothrin, and avermectin, respectively, along with the calculated LC99 diagnostic doses. This resistance risk assessment study suggests that a high risk of lambda-cyhalothrin resistance exists in the field. In addition, a 5-year field investigation of resistance monitoring of L. pratensis was conducted in seven alfalfa regions in farming-pastoral ecotones in northern China. The resistance levels of most populations were very low for phoxim, methomyl, and avermectin, with an upward trend for lambda-cyhalothrin resistance in the DK (Dengkou County), TKT (Tuoketuo County), XL (Xilinhot), and LX (Linxi County) populations during 2015-2019, and medium resistance level to imidacloprid in the TKT population in five years we sampled. The study provided information on chemical control, lambda-cyhalothrin resistance development, baseline susceptibility, and the status of resistance to five commonly-used insecticides against L. pratensis. These results could be used to optimize pyrethroid insecticide use as part of a pest integrated resistance management strategy against this key insect pest of alfalfa.

LABORATORY TOXICITY OF MOSQUITO ADULTICIDES TO THE ASIAN TIGER MOSQUITOES, AEDES ALBOPICTUS AND THE HONEY BEES, APIS MELLIFERA

Aedes albopictus and Apis mellifera were exposed to six insecticide active ingredients and five commercial insecticide formulations by topical application and insecticide-impregnated paper strips respectively to determine the differential toxicity and the potential use of the two methods in insecticide resistance monitoring surveys. By topical application deltamethrin was the most toxic active ingredient (LD 50 = 0.018 µg/g) for Ae. albopictus whereas chlorpyrifos was the least toxic (LD 50 = 0.499 µg/g). For Apis mellifera, the most toxic active ingredients were bifenthrin (LD 50 = 0.047 µg/g) and deltamethrin (LD 50 = 0.055 µg/g) while chlorpyrifos (LD 50 = 0.215 µg/g) and permethrin (LD 50 = 0.287 µg/g) had comparatively low toxicity. When the insecticide-impregnated method was used, Mosquito Mist (a.i. chlorpyrifos) was the most toxic commercial formulation for both Ae. albopictus (LC50 = 0.028 µg/cm2 ) and A. mellifera (LC50 = 0.059 µg/ cm2 ). Duet and DeltaGard showed the least toxicity (LC50 = 2.429 µg/cm 2 and LC50 = 0.491 µg/cm 2 respectively) for Ae. albopictus and DeltaGard was the least toxic to A. mellifera (LC50 = 18.09 µg/cm2 ).&#x0D; When using the topical application method with insecticide active ingredients, more than 3 times permethrin and deltamethrin were required to obtain the same mortality rate in A. mellifera as in Ae. albopictus. However, chlorpyrifos was more toxic for A. mellifera than for Ae. albopictus. In the insecticide-impregnated paper-strip method with commercial insecticide formulations, more than 36 times of DeltaGard was required to obtain the same mortality rate in A. mellifera as in Ae. albopictus. Even though the Mosquito Mist is the most toxic commercial formulation for both insect species, A. mellifera were more than 2 times tolerant to this insecticide compared to Ae. albopictus.&#x0D; The study concludes the active ingredient deltamethrin or its commercial formulation DeltaGard is the best among tested insecticides to control Ae. albopictus with minimal effects to A. mellifera.

Determination of insecticide resistance in Bemisia tabaci (Hemiptera: Aleyrodidae) populations from Punjab, Pakistan

The whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is one of the most important crop pest among the 100 worst invasive species which threatens agriculture worldwide and poses a serious threat to global food security. The control of B. tabaci depends on the insecticide applications in Pakistan, therefore, monitoring of insecticide resistance is essential for achieving control and for managing resistance. In current study, the field populations of B. tabaci from three crops (cotton, okra and tomato) were collected in five districts (Bahawalpur, Lodhran, Multan, Vehari and Faisalabad) of Punjab, Pakistan in 2017, 2018 and 2019. A leaf- dip bioassay was used to determine the resistance of these populations to five insecticides (Diafenthiuron, spirotetramat, deltamethrin, abamectin and nitenpyram). A very low to low level of resistance to nitenpyram, spirotetramat, and abamectin, whereas moderate to high level of resistance to diafenthiuron and deltamethrin were detected in all populations of B. tabaci compared with the laboratory susceptible strain. The resistance ratios ranged 16.37 to 26.07-fold for diafenthiuron, 52.76 to 73.85-fold for deltamethrin, 3.85 to 7.79-fold for nitenpyram, 3.62 to 13.75-fold for spirotetramat and 5.19 to 9.09-fold for abamectin. The presented results will be helpful to make decision on the proper usage of insecticides against whitefly control and to reduce the development of insecticide resistance.

Operationalization of Insecticide Resistance Monitoring Amongst Malaria Vectors in the Philippines

Background: Insecticide-based vector control interventions, insecticide-treated nets and indoor residual spraying have been documented to reduce malaria incidence propelling the Philippines towards malaria elimination. These gains should however be sustained by the prevention, retardation and management of insecticide resistance that may cause revulsion in disease and mortality. It is therefore imperative to track development of resistance and monitor their frequencies and distribution. Methods: Three methods were explored to monitor resistance in malaria vectors: dose response assays, use of knockdown time and the WHO standard bioassay method using diagnostic concentrations. Results: Local discriminating dose of 0.01% was established on Anopheles flavirostris for both alphacypermethrin and deltamethrin. Use of knockdown time showed differences in susceptibilities across strains. Results from WHO standard bioassay method across different provincial sites generally showed susceptibility of An. flavirostris strains to pyrethroids (permethrin, deltamethrin, cyfluthrin, lambdacyhalothrin and etofenprox), organophosphates (malathion and fenitrothion), carbamates (propoxur and bendiocarb) and the organochlorine compound (DDT). However, resistance was detected in several strains of An. flavirostris and An. maculatus s.l. to some of the pyrethroids tested. Conclusion: Continuous monitoring of insecticide resistance captures trends that signals for change in vector control options. It is highly recommended that behavioral changes of target vectors be also observed to decipher if the real cause of resistance is physiological rather than avoidance.

Insecticide resistance status of Aedes aegypti in Bangladesh

BackgroundArboviral diseases, including dengue and chikungunya, are major public health concerns in Bangladesh where there have been unprecedented levels of transmission reported in recent years. The primary approach to control these diseases is to control the vector Aedes aegypti using pyrethroid insecticides. Although chemical control has long been practiced, no comprehensive analysis of Ae. aegypti susceptibility to insecticides has been conducted to date. The aim of this study was to determine the insecticide resistance status of Ae. aegypti in Bangladesh and investigate the role of detoxification enzymes and altered target site sensitivity as resistance mechanisms.MethodsEggs of Aedes mosquitoes were collected using ovitraps from five districts across Bangladesh and in eight neighborhoods of the capital city Dhaka, from August to November 2017. CDC bottle bioassays were conducted for permethrin, deltamethrin, malathion, and bendiocarb using 3- to 5-day-old F0–F2 non-blood-fed female mosquitoes. Biochemical assays were conducted to detect metabolic resistance mechanisms, and real-time PCR was performed to determine the frequencies of the knockdown resistance (kdr) mutations Gly1016, Cys1534, and Leu410.ResultsHigh levels of resistance to permethrin were detected in all Ae. aegypti populations, with mortality ranging from 0 to 14.8% at the diagnostic dose. Substantial resistance continued to be detected against higher (2×) doses of permethrin (5.1–44.4% mortality). Susceptibility to deltamethrin and malathion varied between populations while complete susceptibility to bendiocarb was observed in all populations. Significantly higher levels of esterase and oxidase activity were detected in most of the test populations as compared to the susceptible reference Rockefeller strain. A significant association was detected between permethrin resistance and the presence of Gly1016 and Cys1534 homozygotes. The frequency of kdr (knockdown resistance) alleles varied across the Dhaka Aedes populations. Leu410 was not detected in any of the tested populations.ConclusionsThe detection of widespread pyrethroid resistance and multiple resistance mechanisms highlights the urgency for implementing alternate Ae. aegypti control strategies. In addition, implementing routine monitoring of insecticide resistance in Ae. aegypti in Bangladesh will lead to a greater understanding of susceptibility trends over space and time, thereby enabling the development of improved control strategies.Graphical

Monitoring insecticide resistance in malaria vectors in Shandong Province: approaching malaria elimination.

Monitoring insecticide resistance in malaria vectors in Shandong Province: approaching malaria elimination.

Assessment of the susceptibility status of Aedes aegypti (Diptera: Culicidae) populations to pyriproxyfen and malathion in a nation-wide monitoring of insecticide resistance performed in Brazil from 2017 to 2018

BackgroundChemical mosquito control using malathion has been applied in Brazil since 1985. To obtain chemical control effectiveness, vector susceptibility insecticide monitoring is required. This study aimed to describe bioassay standardizations and determine the susceptibility profile of Ae. aegypti populations to malathion and pyriproxyfen, used on a national scale in Brazil between 2017 and 2018, and discuss the observed impacts in arbovirus control.MethodsThe diagnostic-doses (DD) of pyriproxyfen and malathion were determined as the double of adult emergence inhibition (EI) and lethal doses for 99% of the Rockefeller reference strain, respectively. To monitor natural populations, sampling was performed in 132 Brazilian cities, using egg traps. Colonies were raised in the laboratory for one or two generations (F1 or F2) and submitted to susceptibility tests, where larvae were exposed to the pyriproxyfen DD (0.03 µg/l) and adults, to the malathion DD determined in the present study (20 µg), in addition to the one established by the World Health Organization (WHO) DD (50 µg) in a bottle assay. Dose-response (DR) bioassays with pyriproxyfen were performed on populations that did not achieve 98% EI in the DD assays.ResultsSusceptibility alterations to pyriproxyfen were recorded in six (4.5%) Ae. aegypti populations from the states of Bahia and Ceará, with Resistance Ratios (RR95) ranging from 1.51 to 3.58. Concerning malathion, 73 (55.3%) populations distributed throughout the country were resistant when exposed to the local DD 20 µg/bottle. On the other hand, no population was resistant, and only 10 (7.6%) populations in eight states were considered as exhibiting decreased susceptibility (mortality ratios between 90 and 98%) when exposed to the WHO DD (50 µg/bottle).ConclusionsThe feasibility of conducting an insecticide resistance monitoring action on a nation-wide scale was confirmed herein, employing standardized and strongly coordinated sampling methods and laboratory bioassays. Brazilian Ae. aegypti populations exhibiting decreased susceptibility to pyriproxyfen were identified. The local DD for malathion was more sensitive than the WHO DD for early decreased susceptibility detection.

Monitoring Insecticide Resistance and Target Site Mutations of L1014 Kdr And G119 Ace Alleles in Five Mosquito Populations in Korea.

Mosquitoes are globally distributed and important vectors for the transmission of many human diseases. Mosquito control is a difficult task and the cost of preventing mosquito-borne diseases is much lower than that for curing the associated diseases. Thus, chemical control remains the most effective tool for mosquito. Due to the long-term intensive use of insecticides to control mosquito vectors, resistance to most chemical insecticides has been reported. This study aimed to investigate the relationship between insecticide resistance and target site mutation of L1014 kdr and G119 ace alleles in 5 species/species group of mosquitoes (Aedes vexans, Ae. albopictus, Anopheles spp., Culex pipiens complex, and Cx. tritaeniorhynchus) obtained from 6 collection sites. For Anopheles spp., the proportion of mosquitoes with mutated alleles in L1014 was 88.4%, homozygous resistant genotypes were observed in 46.7%, and heterozygous resistant genotypes were observed in 41.8%. For the Cx. pipiens complex and Cx. tritaeniorhynchus species, homozygous resistant genotypes were found in 25.9% and 9.8%, respectively. However, target site mutation of L1014 in the Ae. vexans nipponii and Ae. albopictus species was not observed. Anopheles spp., Cx. pipiens complex, and Cx. tritaeniorhynchus mosquitoes were resistant to deltamethrin and chlorpyriphos, whereas Ae. vexans nipponii and Ae. albopictus were clearly susceptible. We also found a correlation between the resistance phenotype and the presence of the L1014 kdr and G119 ace mutations only in the Anopheles spp. population. In this study, we suggest that insecticide resistance poses a growing threat and resistance management must be integrated into all mosquito control programs.

The Impact of Insecticide Pre-Exposure on Longevity, Feeding Succession, and Egg Batch Size of Wild Anopheles gambiae s.l.

Background Insecticide resistance among the vector population is the main threat to existing control tools available. The current vector control management options rely on applications of recommended public health insecticides, mainly pyrethroids through long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). Regular monitoring of insecticide resistance does not provide information on important factors that affect parasite transmission. Such factors include vector longevity, vector competence, feeding success, and fecundity. This study investigated the impacts of insecticide resistance on longevity, feeding behaviour, and egg batch size of Anopheles gambiae s.l. Method The larval sampling was conducted in rice fields using a standard dipper (350 ml) and reared to adults in field insectary. A WHO susceptibility test was conducted using standard treated permethrin (0.75%) and deltamethrin (0.05%) papers. The susceptible Kisumu strain was used for reference. Feeding succession and egg batch size were monitored for all survivors and control. Results The results revealed that mortality rates declined by 52.5 and 59.5% for permethrin and deltamethrin, respectively. The mortality rate for the Kisumu susceptible strain was 100%. The survival rates of wild An. gambiae s.l. was between 24 and 27 days. However, the Kisumu susceptible strain blood meal feeding was significantly higher than resistant colony (t = 2.789, df = 21, P=0.011). Additionally, the susceptible An. gambiae s.s. laid more eggs than the resistant An.gambiae s.l. colony (Χ2 = 1366, df = 1, P ≤ 0.05). Conclusion It can, therefore, be concluded that the wild An. gambiae s.l. had increased longevity, blood feeding, and small egg batch size compared to Kisumu susceptible colonies.

Pyrethroid and Carbamate Resistance in Anopheles funestus Giles along Lake Kariba in Southern Zambia.

.Whereas data on insecticide resistance and its underlying mechanisms exist for parts of Zambia, data remain limited in the southern part of the country. This study investigated the status of insecticide resistance, metabolic mechanisms, and parasite infection in Anopheles funestus along Lake Kariba in southern Zambia. Indoor-resting mosquitoes were collected from 20 randomly selected houses within clusters where a mass drug administration trial was conducted and raised to F1 progeny. Non–blood-fed 2- to 5-day-old female An. funestus were exposed to WHO insecticide-impregnated papers with 0.05% deltamethrin, 0.1% bendiocarb, 0.25% pirimiphos-methyl, or 4% dichloro-diphenyl-trichloroethane (DDT). In separate assays, An. funestus were pre-exposed to piperonyl butoxide (PBO) to determine the presence of monooxygenases. Wild-caught An. funestus that had laid eggs for susceptibility assays were screened for circumsporozoite protein of Plasmodium falciparum by ELISA, and sibling species were identified by polymerase chain reaction. Anopheles funestus showed resistance to deltamethrin and bendiocarb but remained susceptible to pirimiphos-methyl and DDT. The pre-exposure of An. funestus to PBO restored full susceptibility to deltamethrin but not to bendiocarb. The overall sporozoite infection rate in An. funestus populations was 5.8%. Detection of pyrethroid and carbamate resistance in An. funestus calls for increased insecticide resistance monitoring to guide planning and selection of effective insecticide resistance management strategies. To prevent the development of resistance and reduce the underlying vectorial capacity of mosquitoes in areas targeted for malaria elimination, an effective integrated vector management strategy is needed.

Determination of insecticides' lethal concentrations and metabolic enzyme levels in Triatoma dimidiata.

The feasibility of the use of WHO impregnated paper and biochemical assays to determine lethal concentrations (LC50 and LC99) and insecticide metabolic enzyme levels of Triatoma dimidiata. LC50 and LC99 were calculated with WHO papers impregnated at different concentrations of malathion, propoxur and deltamethrin; the percentage of insensitive acetylcholinesterase (iAChE); and the levels of esterases, glutathione S-transferases, and monooxygenases in laboratory nymphs of the first stage (5 to 7 days), were undertaken using the WHO biochemical assays. Respectively the LC50 and LC99 μg/cm2 obtained for malathion were 43.83 and 114.38, propoxur 4.71 and 19.29, and deltamethrin 5.80 and 40.46. A 30% of the population had an iAChE, and only a few individuals had high P450 and β-eterase levels. Impregnated papers and biochemical tests developed by WHO for other insects, proved to be feasible methods in monitoring insecticide resistance and metabolic enzymes involved in T. dimidiata.

Monitoring insecticide resistance and endosymbiont composition in greenhouse populations of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) from Mersin, Turkey

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a destructive pest that causes significant damage on important agricultural crops through direct feeding, honeydew excretion and plant virus transmission. Chemical control is among the most widely used methods to suppress whitefly infestations but management efforts have become very challenging due to the development of insecticide resistance. This study was conducted to monitor insecticide resistance and detect endosymbiont composition in greenhouse-collected B. tabaci populations from Mersin, Turkey. All greenhouse-collected populations were identified as Middle East-Asia Minor 1 (MEAM-1). Based on Resistance ratios (RRs) of LC50 values, all greenhouse-collected populations were low to moderately resistant to the three neonicotinoids when compared to the reference population. Resistance ratios were in the range of 3.63–8.79-fold for acetamiprid; 7.29–15.29-fold for imidacloprid and 9.74–11.79-fold for thiamethoxam after 72 h of exposure. No or very low levels of resistance (RR ≤ 2.00) were detected for spinetoram, spinosad and sulfoxaflor. Spinetoram was the most toxic of all the other tested insecticides against all populations. Generally, LC90 values obtained for greenhouse-collected populations were much higher than the recommended concentrations of the neonicotinoids but lower for spinetoram, spinosad and sulfoxaflor. Molecular analysis of endosymbionts indicated that all populations were infected with Portiera and Hamiltonella, whereas only two out of five greenhouse-collected populations were infected with Rickettsia. The insecticide-susceptible lab strain had relatively the highest rate of Rickettsia infections. Moreover, a statistically significant negative correlation was detected between LC50 values and the rate of Rickettsia infections for imidacloprid and thiamethoxam (R = −0.930 and R = −0.866, respectively), while the relationship was non-significant for acetamiprid resistance (R = −0.598).

The V1016G mutation of the voltage-gated sodium channel (VGSC) gene contributes to the insecticide resistance of Aedes aegypti from Makassar, Indonesia.

Aedes aegypti represents one of the main vectors of at least five relevant arthropod-borne viral infections in humans (i.e., Rift Valley fever, Dengue fever, Zika, chikungunya, and yellow fever) worldwide. Ae. aegypti control strategies are mostly based on using chemical insecticides (i.e., organophosphates, pyrethroids, carbamates, and organochlorines) and reducing larval sources. Furthermore, monitoring the growth activity and mapping the geographical distribution of insecticide resistance are mandatory, as recommended by the WHO. Accordingly, we conducted a study on the possible mechanism by which Ae. aegypti develops resistance to several frequently used chemical insecticides (i.e., λ-cyhalothrin, bendiocarb, cyfluthrin, deltamethrin, malathion, and permethrin) in the city of Makassar, Sulawesi, Indonesia. The results showed the progression of resistance toward the examined insecticides in Ae. aegypti populations in Makassar. The mortality rate of Ae. aegypti was less than 90%, with the highest resistance recorded against 0.75% permethrin. The molecular evaluation of the voltage-gated sodium channel gene (VGSC) showed a significant correlation of the V1016G gene mutation in the tested 0.75% permethrin-resistant Ae. aegypti phenotypes. Nevertheless, the F1534C point mutation in the VGSC gene of Ae. aegypti did not show a significant correlation with the phenotype exhibiting insecticide resistance to 0.75% permethrin. These results indicate that Ae. aegypti mosquitoes in Makassar City have developed resistance against the frequently used insecticide permethrin, which might spread to less-populated regions of Sulawesi. Therefore, we call for further entomological monitoring of insecticide resistance not only on Sulawesi but also on other closely located islands of the Indonesian archipelago to delay the spread of Ae. aegypti insecticide resistance.