Search

Public health responses are not purely technical undertakings; these responses happen within and are affected by their social and economic contexts. Whether or not these efforts succeed depends on public [...]

Aedes albopictus, also known as the Asian tiger mosquito, is indigenous to the tropical forests of Southeast Asia. Ae. albopictus is expanding across the globe at alarming rates, raising concern over the transmission of mosquito-borne diseases, such as dengue, West Nile fever, yellow fever, and chikungunya fever. Since Ae. albopictus was reported in Houston (Harris County, Texas) in 1985, this species has rapidly expanded to at least 32 states across the United States. Public health efforts aimed at controlling Ae. albopictus, including surveillance and adulticide spraying operations, occur regularly in Harris County. Despite rotation of insecticides to mitigate the development of resistance, multiple mosquito species including Culex quinquefasciatus and Aedes aegypti in Harris County show organophosphate and pyrethroid resistance. Aedes albopictus shows relatively low resistance levels as compared to Ae. aegypti, but kdr-mutation and the expression of detoxification genes have been reported in Ae. albopictus populations elsewhere. To identify potential candidate detoxification genes contributing to metabolic resistance, we used RNA sequencing of field-collected malathion-resistant and malathion-susceptible, and laboratory-maintained susceptible colonies of Ae. albopictus by comparing the relative expression of transcripts from three major detoxification superfamilies involved in malathion resistance due to metabolic detoxification. Between these groups, we identified 12 candidate malathion resistance genes and among these, most genes correlated with metabolic detoxification of malathion, including four P450 and one alpha esterase. Our results reveal the metabolic detoxification and potential cuticular-based resistance mechanisms associated with malathion resistance in Ae. albopictus in Harris County, Texas. Author summary: The Asian tiger mosquito, Aedes albopictus, is an invasive species rapidly expanding worldwide. It is the main vector for several arboviruses, including dengue virus, Zika virus, and chikungunya virus. These viral diseases pose a substantial threat to global public health. Ae. albopictus has developed resistance to insecticides such as malathion, making its control more challenging. To uncover the genetic basis of this resistance, we conducted a study using RNA sequencing-based transcriptome profiling. In this study, we obtained gene expression patterns in malathion-resistant and susceptible mosquitoes. The transcriptomic information allowed us to identify potential key genes in detoxification gene families associated with metabolic resistance to malathion. Our discovery provides insights into the molecular mechanisms behind malathion resistance in Ae. albopictus. Our research not only contributes to the understanding of mosquito biology and control but also highlights the future direction for continued efforts in developing innovative strategies to mitigate rapid development of insecticide resistance in Ae. albopictus. [ABSTRACT FROM AUTHOR]

Introduction: Culex quinquefasciatus is a mosquito species of significant public health importance due to its ability to transmit multiple pathogens that can cause mosquito-borne diseases, such as West Nile fever and St. Louis encephalitis. In Harris County, Texas, Cx. quinquefasciatus is a common vector species and is subjected to insecticide-based management by the Harris County Public Health Department. However, insecticide resistance in mosquitoes has increased rapidly worldwide and raises concerns about maintaining the effectiveness of vector control approaches. This concern is highly relevant in Texas, with its humid subtropical climate along the Gulf Coast that provides suitable habitat for Cx. quinquefasciatus and other mosquito species that are known disease vectors. Therefore, there is an urgent and ongoing need to monitor the effectiveness of current vector control programs. Methods: In this study, we evaluated the impact of vector control approaches by estimating the effective population size of Cx. quinquefasciatus in Harris County. We applied Approximate Bayesian Computation to microsatellite data to estimate effective population size. We collected Cx. quinquefasciatus samples from two mosquito control operation areas; 415 and 802, during routine vector monitoring in 2016 and 2017. No county mosquito control operations were applied at area 415 in 2016 and 2017, whereas extensive adulticide spraying operations were in effect at area 802 during the summer of 2016. We collected data for eighteen microsatellite markers for 713 and 723 mosquitoes at eight timepoints from 2016 to 2017 in areas 415 and 802, respectively. We also investigated the impact of Hurricane Harvey’s landfall in the Houston area in August of 2017 on Cx. quinquefasciatus population fluctuation. Results: We found that the bottleneck scenario was the most probable historical scenario describing the impact of the winter season at area 415 and area 802, with the highest posterior probability of 0.9167 and 0.4966, respectively. We also detected an expansion event following Hurricane Harvey at area 802, showing a 3.03-fold increase in 2017. Discussion: Although we did not detect significant effects of vector control interventions, we found considerable influences of the winter season and a major hurricane on the effective population size of Cx. quinquefasciatus. The fluctuations in effective population size in both areas showed a significant seasonal pattern. Additionally, the significant population expansion following Hurricane Harvey in 2017 supports the necessity for post-hurricane vectorcontrol interventions. [ABSTRACT FROM AUTHOR]

BACKGROUND: Pyrethroids are among the most applied adulticides worldwide to control mosquito vectors for prevention of arboviral diseases transmission. However, pesticide resistance development in a mosquito population could lead to decreased control efficacy. While most studies investigate the resistant genotype (i.e. kdr, CYP450, etc.) as explanatory variables, few field efficacy studies have measured pesticide quantities deposited at different distances from the sprayer in association with observed mosquito mortality. The current study determined field delivered amounts of an applied ULV permethrin/PBO formulation (31% permethrin + 66% piperonyl butoxide) by GC/MS and estimated practical resistance ratios using caged mosquito females. RESULTS: For field samples, the extraction method recovered 78 ± 3.92–108 ± 8.97% of the permethrin/PBO formulation when utilizing the peaks of PBO from GC/MS to estimate the concentrations of adulticide deposited near the mosquito cages. The field bioassay showed that the spatial distribution of permethrin/PBO formulation was heterogeneous among three pseudo‐replicates within the same distance. Within the quantifiable permethrin/PBO range of 15.7–51.4 ng/cm2, field‐collected mosquito mortalities started at 64% and linearly increased reaching 100% only in two areas, while all Sebring susceptible mosquitoes died. The field LC95 resistance ratio (RR) of F0Cx. quinquefasciatus ranged from 2.65–3.51, falling within the 95% CI of RR95 estimated by laboratory vial assays. Tests with and without PBO indicated P450's enzymes contributed to field resistance. CONCLUSION: Results showed the suitability of the collection and quantification method to estimate the field resistance ratio at the applied pesticide rate. Pesticide quantification would also allow the association of the known frequencies of resistance mechanisms (e.g. kdr, CYP450) with field mortalities to estimate the resistance level conferred by such mechanisms. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Harris County, TX, is the third most populous county in the USA and upon detection of arboviruses Harris County Public Health applies insecticides (e.g., pyrethroid-based Permanone 31–66) against adults of Culex quinquefasciatus to prevent disease transmission. Populations of Aedes aegypti, while not yet a target of public health control, are likely affected by pyrethroid exposure. As this species is a vector of emerging arboviruses, its resistance status to Permanone and the kdr mutations in the voltage-gated sodium channel (VGSC) associated with pyrethroid resistance were investigated. We examined females of known genotype at the V1016I and F1534C sites (N = 716) for their genotype at the 410 amino acid position in the VGSC, and for the influence of their kdr genotype on survival to Permanone at three different distances from the insecticide source in field tests. Most females (81.8%) had at least one resistant L allele at the 410 position, being the first report of the V410L mutation in Ae. aegypti for Texas. When only genotypes at the 410 position were analyzed, the LL genotype exhibited higher survivorship than VL or VV. Out of 27 possible tri-locus kdr genotypes only 23 were found. Analyses of the probability of survival of tri-locus genotypes and for the V410L genotype using a multivariate logistic regression model including area, distance, and genotype found significant interactions between distance and genotype. When only the most common tri-locus genotypes were analyzed (LL/II/CC, 48.2%; VL/II/CC, 19.1%; and VV/II/CC, 10.1%) genotype had no effect on survival, but significant interactions of distance and genotype were found. This indicated that the V410L kdr allele increased survival probability at certain distances. Genotypes did not differ in survivorship at 7.62-m, but LL/II/CC had higher survivorship than VL/II/CC at 15.24- and 22.86-m. The model also identified differences in survivorship among the operational areas investigated. Author summary: Preventing Aedes aegypti populations from spreading arboviruses in highly populated areas primarily relies upon chemical control with insecticides, such as pyrethroids, applied by public health agencies to target the female mosquito vector. However, the development of insecticide resistance in mosquito populations jeopardizes these vector control strategies. The impact of the different kdr mutations conferring resistance to pyrethroids on the survival of Ae. aegypti in the field is not fully understood. We previously found that two knockdown resistance (kdr) mutations in the voltage gated sodium channel (VGSC) did not increase survivorship in field cage tests despite their widespread presence and high frequency. In this paper, we report the first detection of the V410L kdr mutation in combination with the V1016I and F1534C genotypes. Most females were detected with kdr mutations at one, two or three of these sites in the VGSC. Genotyping females after insecticide application in field cage tests showed that the V410L mutations were associated with higher survivorship only at the 15.24- and 22.86-meter distances from the source of the spray application, as we observed that the LL/II/CC genotype had higher survivorship than the VL/II/CC genotype at these distances. [ABSTRACT FROM AUTHOR]

Among disease vectors, Aedes aegypti (L.) (Diptera: Culicidae) is one of the most insidious species in the world. The disease burden created by this species has dramatically increased in the past 50 years, and during this time countries have relied on pesticides for control and prevention of viruses borne by Ae. aegypti. The small number of available insecticides with different modes of action had led to increases in insecticide resistance, thus, strategies, like the "Incompatible Insect Technique" using Wolbachia's cytoplasmic incompatibility are desirable. We evaluated the effect of releases of Wolbachia infected Ae. aegypti males on populations of wild Ae. aegypti in the metropolitan area of Houston, TX. Releases were conducted by the company MosquitoMate, Inc. To estimate mosquito population reduction, we used a mosquito abundance Bayesian hierarchical estimator that accounted for inefficient trapping. MosquitoMate previously reported a reduction of 78% for an intervention conducted in Miami, FL. In this experiment we found a reduction of 93% with 95% credibility intervals of 86% and 96% after six weeks of continual releases. A similar result was reported by Verily Life Sciences, 96% [94%, 97%], in releases made in Fresno, CA. Author summary: Aedes aegypti is one of the most important mosquito species because females can potentially carry pathogens that cause disease. These diseases have a tremendous impact worldwide making this species an important target of control. We evaluated a mosquito control strategy independently of the company that developed the method while the company tested it in Harris County, TX. The strategy relies on a bacterium (Wolbachia sp) that causes changes in the sperm of infected males, preventing uninfected female mosquitoes from producing viable eggs (phenomenon known as cytoplasmic incompatibility). Wolbachia-infected males are released in large numbers (inundative releases) to outcompete wild-type Wolbachia-free males and reduce the population of existing Ae. aegypti mosquitoes. We observed a sustained reductions > 90% in the number of females very likely because of the intervention conducted in Harris County, TX. The results we observed were very similar to observations made by others in Miami, FL and in Fresno, CA. However, more experiments (following randomized cluster designs) should be performed to increase the statistical power while controlling for environmental factors that could contribute to fluctuations in mosquito populations and trapping variations. [ABSTRACT FROM AUTHOR]

Aedes aegypti (L.) is an important mosquito vector of emerging arboviruses such as Zika, dengue, yellow fever, and chikungunya. To quell potential disease outbreaks, its populations are controlled by applying pyrethroid insecticides, which selection pressure may lead to the development of insecticide resistance. Target site insensitivity to pyrethroids caused by non-synonymous knockdown resistance (kdr) mutations in the voltage-gated sodium (NaV) channel is a predominant mechanism of resistance in mosquitoes. To evaluate the potential impact of pyrethroid resistance on vector control, Ae. aegypti eggs were collected from eight mosquito control operational areas in Harris County, Texas, and emerged females were treated in field tests at four different distances from the pyrethroid Permanone 31–66 source. The females were genotyped by melting curve analyses to detect two kdr mutations (V1016I and F1534C) in the NaV channel. Harris County females had higher survivorship rates at each distance than the pyrethroid-susceptible Orlando strain females. Survivorship increased with distance from the pyrethroid source, with 39% of field-collected mosquitoes surviving at 7.62 m and 82.3% at 22.86 m from the treatment source. Both the V1016I and F1534C pyrethroid resistant genotypes were widely distributed and at high frequency, with 77% of the females being double homozygous resistant (II/CC), this being the first report of kdr mutations in Ae. aegypti in Harris County. Analysis of the probability of survival for each mutation site independently indicated that the CC genotype had similar probability of survival as the FC heterozygous, while the II genotype had higher survival than both the VI and VV, that did not differ. The double homozygous resistant genotype (II/CC) had the highest probability of survival. A linear model estimated probability of survival for areas and genotypes. The high frequency and widespread distribution of double-homozygote pyrethroid-resistant Ae. aegypti may jeopardize disease vector control efforts in Harris County. Author summary: Females of the mosquito Aedes aegypti transmit arboviruses of human diseases including Zika, dengue, chikungunya, and yellow fever, and Culex quinquefasciatus transmits West Nile virus (WNV). Upon WNV detection in Harris County, TX, Harris County Public Health Mosquito and Vector Control Division applies pyrethroid or organophosphate insecticides to control Cx. quinquefasciatus mosquitoes. Pyrethroids target the sodium channel and knockdown resistance (kdr) mutations in this channel confer resistance to pyrethroids and increase mosquito survival. While Ae. aegypti is not a current target for public mosquito control in Harris County, we investigated frequency and spatial distribution of two kdr mutations in Ae. aegypti females, and their impact on pyrethroid survival after field tests were conducted with Permanone 31–66. The survival probability of mosquitoes varied depending on distance from application, and on their genotype and area of origin. Survivorship was lowest at 7.62 m, but most females survived at and beyond 15.24 m. Most (98.3%) females genotyped carried at least one kdr allele, and 77% were double homozygous resistant (II/CC). This is the first report of these resistant genotypes in Harris County. The resistant genotype II/CC had the highest survival probability. These results should be useful when modeling the risk of mosquito-borne diseases. [ABSTRACT FROM AUTHOR]

West Nile virus (WNV) is a globally distributed mosquito-borne virus of great public health concern. The number of WNV human cases and mosquito infection patterns vary in space and time. Many statistical models have been developed to understand and predict WNV geographic and temporal dynamics. However, these modeling efforts have been disjointed with little model comparison and inconsistent validation. In this paper, we describe a framework to unify and standardize WNV modeling efforts nationwide. WNV risk, detection, or warning models for this review were solicited from active research groups working in different regions of the United States. A total of 13 models were selected and described. The spatial and temporal scales of each model were compared to guide the timing and the locations for mosquito and virus surveillance, to support mosquito vector control decisions, and to assist in conducting public health outreach campaigns at multiple scales of decision-making. Our overarching goal is to bridge the existing gap between model development, which is usually conducted as an academic exercise, and practical model applications, which occur at state, tribal, local, or territorial public health and mosquito control agency levels. The proposed model assessment and comparison framework helps clarify the value of individual models for decision-making and identifies the appropriate temporal and spatial scope of each model. This qualitative evaluation clearly identifies gaps in linking models to applied decisions and sets the stage for a quantitative comparison of models. Specifically, whereas many coarse-grained models (county resolution or greater) have been developed, the greatest need is for fine-grained, short-term planning models (m–km, days–weeks) that remain scarce. We further recommend quantifying the value of information for each decision to identify decisions that would benefit most from model input. [ABSTRACT FROM AUTHOR]

Culex quinquefasciatus is one of the most important mosquito vectors of arboviruses. Currently, the fastest approach to control disease transmission is the application of synthetic adulticide insecticides. However, in highly populated urban centers the development of insecticide resistance in mosquito populations could impair insecticide efficacy and therefore, disease control. To assess the effect of resistance on vector control, females of Cx. quinquefasciatus collected from six mosquito control operational areas in Harris County, Texas, were treated in field cage tests at three different distances with the pyrethroid Permanone® 31–66 applied at the operational rate. Females were analyzed by sequencing and/or diagnostic PCR using de novo designed primers for detecting the kdr-like mutation in the voltage-gated sodium channel (L982F; TTA to TTT) (house fly kdr canonical mutation L1014F). Females from the Cx. quinquefasciatus susceptible Sebring strain and those from the six operational areas placed at 30.4 m from the treatment source were killed in the tests, while 14% of field-collected mosquitoes survived at 60.8 m, and 35% at 91.2 m from the source. The diagnostic PCR had a with 97.5% accuracy to detect the kdr-like mutation. Pyrethroid resistant mosquitoes carrying the L982F mutation were broadly distributed in Harris County at high frequency. Among mosquitoes analyzed (n = 1,028), the kdr-kdr genotype was prevalent (81.2%), the kdr-s genotype was 18%, and s-s mosquitoes were less than 1% (n = 8). A logistic regression model estimated an equal probability of survival for the genotypes kdr-kdr and kdr-s in all areas analyzed. Altogether, our results point to a high-risk situation for the pyrethroid-based arboviral disease control in Harris County. Author summary: Female Culex quinquefasciatus mosquitoes blood-feed preferentially on birds but also on mammals including humans, to which they may transmit pathogenic arboviruses. To prevent transmission of West Nile and/or other viruses in Harris County, TX, the vector control agency applies mosquito adulticides when arboviruses are detected. Insecticide resistance can hinder mosquito control, increasing the risk of disease transmission. Pyrethroid resistant mosquitoes carry kdr-like mutation(s) in the sodium channel, the pyrethroid target site in the nervous system, that increases survival probability. We investigated frequency and spatial distribution of the kdr-like mutation in Harris County mosquitoes, and how they affect pyrethroid survivorship. We conducted field cage tests with a commercial pyrethroid formulation, and developed molecular tests to detect the kdr-like mutation in females from 6 operational areas. In field tests, almost no mosquito survived at 30.4 m, but 14% and 35% of mosquitoes survived at 60.8 m and 91.2 m. We found 99% of mosquitoes carried at least one kdr-like allele. At the high rate of pyrethroid, the survival probability of mosquitoes carrying one or two kdr-like alleles was not statistically different in the six areas, but survival increased significantly with distance. These results should be considered when analyzing risk of disease transmission. [ABSTRACT FROM AUTHOR]

Hurricane Harvey made a landfall on the Texas Gulf Coast on August 25, 2017, stalling over Harris County as a tropical storm for 4 days (August 26–29), dumping approximately 127 cm of rain. This tremendous amount of rainfall overwhelmed the county's natural and man-made drainage systems, resulting in unprecedented widespread flooding. Immediately following, Harris County Public Health Mosquito and Vector Control Division conducted a countywide emergency vector control response by integrating surveillance, control, and education strategies. This included landing rate counts, mosquito and avian surveillance, arbovirus testing, ground-based ultra-low volume (ULV) and aerial pesticide spraying, and community outreach. The immediate response lasted for 4 wk through September, resulting in 774 landing rates, 49,342 ha treated by ground-based ULV, 242,811 ha treated by aerial ULV, 83,241 mosquitoes collected, 1,807 mosquito pools tested, and 20 education/outreach sessions. Recovery activities of 3 additional education/outreach events continued through October while surveillance and control activities returned to routine status. [ABSTRACT FROM AUTHOR]

Microbial interactions are an underappreciated force in shaping insect microbiome communities. Although pairwise patterns of symbiont interactions have been identified, we have a poor understanding regarding the scale and the nature of co-occurrence and co-exclusion interactions within the microbiome. To characterize these patterns in mosquitoes, we sequenced the bacterial microbiome of Aedes aegypti , Ae. albopictus , and Culex quinquefasciatus caught in the field or reared in the laboratory and used these data to generate interaction networks. For collections, we used traps that attracted host-seeking or ovipositing female mosquitoes to determine how physiological state affects the microbiome under field conditions. Interestingly, we saw few differences in species richness or microbiome community structure in mosquitoes caught in either trap. Co-occurrence and co-exclusion analysis identified 116 pairwise interactions substantially increasing the list of bacterial interactions observed in mosquitoes. Networks generated from the microbiome of Ae. aegypti often included highly interconnected hub bacteria. There were several instances where co-occurring bacteria co-excluded a third taxa, suggesting the existence of tripartite relationships. Several associations were observed in multiple species or in field and laboratory-reared mosquitoes indicating these associations are robust and not influenced by environmental or host factors. To demonstrate that microbial interactions can influence colonization of the host, we administered symbionts to Ae. aegypti larvae that either possessed or lacked their resident microbiota. We found that the presence of resident microbiota can inhibit colonization of particular bacterial taxa. Our results highlight that microbial interactions in mosquitoes are complex and influence microbiome composition. [ABSTRACT FROM AUTHOR]

The ground adulticiding program in densely populated Harris County has been employed on the basis of virus-positive mosquitoes almost exclusively using the ‘rotation of chemicals best practices’ stratagem. To evaluate its effectiveness, 15 comparative field cage testing events were conducted from 2011-2015 using seven wild population samples from repeatedly collected locations of Culex quinquefasciatus Say and a laboratory susceptible Sebring strain colony reared to adults. A 3 x 3 plot design was employed for exposure to ultra-low volume applications of malathion and synergized permethrin. No significant differences were found in mortality rate among testing dates, year, row placement, or relative humidity. Mortality was significantly different between adulticides (p<0.001) with mean mortality rates for malathion 96.42% (±7.95%) and permethrin 92.38% (±14.04). There was a significant temperature difference for permethrin (p<0.001) but none for malathion (p=0.644). Mosquito population mortality was statistically different by study operational area (p<0.011) and chemical (p<0.001). Susceptible colony adults used as positive controls downwind strongly aided determination of efficacy and resistance to each adulticide, providing evidence of individual application coverage, though comparative analysis was done with overall mortalities by normal methodology. [ABSTRACT FROM AUTHOR]

The comparative efficacy of ultra-low volume applications of deltamethrin, permethrin, and malathion against specific adult populations of Culex quinquefasciatus, a primary regional vector of Saint Louis encephalitis and West Nile virus, using field cage tests is described. At labeled application rates, the estimated mass median diameters for Fyfanon®, Evoluer™, and DeltaGard® were 18.32, 19.24, and 17.44 μm, respectively. No significant differences ( P ≥ 0.01) in mean percent control were observed across all 3 wild populations and a susceptible Sebring strain tested with Fyfanon, DeltaGard, and Evoluer, providing 98.25%, 98.20%, and 97.24% mean percent control. Mean percent control for Sebring and 3 wild populations was 99.38%, 97.79%, 97.26%, and 97.15%, respectively, which were not significantly different from one another ( P ≥ 0.01). Across all tests, highly significant differences ( P ≤ 0.01) in mean percent control were obtained at 30.48, 60.96, and 91.44 m distances downwind, with mean percent control at 91.44 m being significantly less than that observed at 30.48 m, but not at 60.96 m. Individually, tests for DeltaGard, Fyfanon, and Evoluer resulted in no significant differences ( P ≥ 0.01) in mean percent control between all mosquito populations tested, ranging from 96.47 to 100. However, Evoluer obtained significantly less ( P ≤ 0.01) mean percent control at 91.44 m compared to DeltaGard and Fyfanon. Data suggest that the wild Cx. quinquefasciatus specimens collected were as susceptible as the laboratory Sebring strain. The use of Sebring as positive controls downwind strongly supported determination of the efficacy of all adulticides and susceptibility of wild populations tested. [ABSTRACT FROM AUTHOR]

The Larvasonic™ Field Arm Mobile Wetlands Unit and SD-Mini were tested for efficacy against Culex larvae, and effects on aquatic nontarget organisms (NTO). The Field Arm provided 84.61% to 100% control of caged Culex larvae out to 0.91-m distance in shallow ditches and 60.45% control of Culex larvae at 0.61-m without any effects to caged NTO. Slow ditch treatment achieved 77.35% control compared to fast treatment (20.42%), whereas 77.65% control was obtained along edges of a neglected swimming pool, compared to near the middle (23.97%). In bucket tests, the SD-Mini provided >97% control of Culex and 85.35% reduction of immature giant water bugs, which decreased slightly (83.45%) over the monitoring period, which was not significantly different from cannibalistic damselflies (62.80%), with reduction of both being significantly higher than other NTO tested. There was a small (0.37%) reduction of dragonflies (naiads), due to cannibalism. Both Larvasonic units could effectively augment conventional larvicide operations in smaller areas without causing resistance within mosquito populations or harming NTO when used properly. [ABSTRACT FROM AUTHOR]

The Asian tiger mosquito, Aedes albopictus, is an anthropophilic aggressive daytime-biting nuisance and an efficient vector of certain arboviruses and filarial nematodes. Over the last 30 years, this species has spread rapidly through human travel and commerce from its native tropical forests of Asia to every continent except Antarctica. In 2011, a population of Asian tiger mosquito (Aedes albopictus) was discovered in Los Angeles (LA) County, California. To determine the probable origin of this invasive species, the genetic structure of the population was compared against 11 populations from the United States and abroad, as well as preserved specimens from a 2001 introduction into California using the mitochondrial cytochrome c oxidase 1 (CO1) gene. A total of 66 haplotypes were detected among samples and were divided into three main groups. Aedes albopictus collected in 2001 and 2011 from LA County were genetically related and similar to those from Asia but distinct from those collected in the eastern and southeastern United States. In view of the high genetic similarities between the 2001 and 2011 LA samples, it is possible that the 2011 population represents in part the descendants of the 2001 introduction. There remains an imperative need for improved surveillance and control strategies for this species. [ABSTRACT FROM AUTHOR]

In 2008 and 2009, our current thermal fogging methods and materials were evaluated in underground systems against feral and laboratory strains of adult Culex quinquefasciatus. Culex quinquefasciatus adults collected from storm drain systems the night before treatment were tested concurrently with adults from a susceptible laboratory strain (Sebring) in 10 separate tests. During 2008, there were no significant differences in the low mean percent control obtained between any of the feral populations (29.39%) and susceptible (Sebring) populations (56.04%) tested, whereas in 2009, application of mineral oil alone yielded extremely low, but significantly different mean percent control at 0.99% for ferals and 0.01% for Sebrings. During 2009 mineral oil evaluations, 45,677 droplets were collected in storm drains at distances of 99.1, 50.6, 57.9, 67.7, and 109.7 m from the application site, with 99% of the droplets below 3 microm in diam; additionally, we found no significant differences between mean percent control of Sebring and feral mosquito populations using the higher (3.2×) 1:10 application rate of Pyrocide®. However, mean percent control between the feral and susceptible strain (Sebring) during 2009 was lower than in 2008 at 16.55% for ferals and 24.43% in Sebrings. Results indicated that control methodologies and/or chemicals used were ineffective at controlling Cx. quinquefasciatus in storm drains using the chosen experimental design. Based upon this information, thermal fog operations were discontinued due to lack of effectiveness. [ABSTRACT FROM AUTHOR]

Early warning systems for vector-borne diseases (VBDs) prediction are an ecological application where data from the interface of several environmental components can be used to predict future VBD transmission. In general, models for early warning systems only consider average environmental conditions ignoring variation in weather variables, despite the prediction from Schmalhausen's law about the importance of environmental variability for biological systems. We present results from a long-term mosquito surveillance program from Harris County, Texas, USA, where we use time series analysis techniques to study the abundance and West Nile virus (WNV) infection patterns in the local primary vector, Culex quinquefasciatus Say. We found that, as predicted by Schmalhausen's law, mosquito abundance was associated with the standard deviation and kurtosis of environmental variables. By contrast, WNV infection rates were associated with 8-month lagged temperature, suggesting environmental conditions during overwintering might be key for WNV amplification during summer outbreaks. Finally, model validation showed that seasonal autoregressive models successfully predicted mosquito WNV infection rates up to 2 months ahead, but did rather poorly at predicting mosquito abundance, a result that might reflect impacts of vector control for mosquito population reduction, geographic scale, and other artifacts generated by operational constraints of mosquito surveillance systems. Unlabelled Image • 10,533,033 female Culex quinquefasciatus mosquitoes collected from 2002 to 2015 in Harris County, Texas, USA. • Time series analysis correlates weather, vegetation, mosquito abundance and infection with West Nile virus. • Models suggest increased variability in temperature and rainfall increase mosquito abundance, supporting Schmalhausen's law. • Warmer winter temperatures were related to increased mosquito infection with West Nile virus eight months later. [ABSTRACT FROM AUTHOR]

Introduction: Culex quinquefasciatus is a mosquito species of significant public health importance due to its ability to transmit multiple pathogens that can cause mosquito-borne diseases, such as West Nile fever and St. Louis encephalitis. In Harris County, Texas, Cx. quinquefasciatus is a common vector species and is subjected to insecticide-based management by the Harris County Public Health Department. However, insecticide resistance in mosquitoes has increased rapidly worldwide and raises concerns about maintaining the effectiveness of vector control approaches. This concern is highly relevant in Texas, with its humid subtropical climate along the Gulf Coast that provides suitable habitat for Cx. quinquefasciatus and other mosquito species that are known disease vectors. Therefore, there is an urgent and ongoing need to monitor the effectiveness of current vector control programs. Methods: In this study, we evaluated the impact of vector control approaches by estimating the effective population size of Cx. quinquefasciatus in Harris County. We applied Approximate Bayesian Computation to microsatellite data to estimate effective population size. We collected Cx. quinquefasciatus samples from two mosquito control operation areas; 415 and 802, during routine vector monitoring in 2016 and 2017. No county mosquito control operations were applied at area 415 in 2016 and 2017, whereas extensive adulticide spraying operations were in effect at area 802 during the summer of 2016. We collected data for eighteen microsatellite markers for 713 and 723 mosquitoes at eight timepoints from 2016 to 2017 in areas 415 and 802, respectively. We also investigated the impact of Hurricane Harvey's landfall in the Houston area in August of 2017 on Cx. quinquefasciatus population fluctuation. Results: We found that the bottleneck scenario was the most probable historical scenario describing the impact of the winter season at area 415 and area 802, with the highest posterior probability of 0.9167 and 0.4966, respectively. We also detected an expansion event following Hurricane Harvey at area 802, showing a 3.03-fold increase in 2017. Discussion: Although we did not detect significant effects of vector control interventions, we found considerable influences of the winter season and a major hurricane on the effective population size of Cx. quinquefasciatus . The fluctuations in effective population size in both areas showed a significant seasonal pattern. Additionally, the significant population expansion following Hurricane Harvey in 2017 supports the necessity for post-hurricane vector-control interventions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Huang, Athrey, Kaufman, Fredregill and Slotman.)

As observed in many locations worldwide, resistance to pyrethroids is common in Aedes aegypti (L.) in the southern United States and northern Mexico. Strong resistance in Aedes albopictus (Skuse) is less common and is not as well characterized. These 2 species have been undergoing range expansion and are sympatric in many locations including Houston, Texas. They are often collected from the same locations and lay eggs in the same larval habitats. In this study, we colonized both Ae. aegypti and Ae. albopictus from 4 locations in Houston and characterized insecticide resistance using permethrin as a model pyrethroid. We found differences in resistance intensity between the species at all 4 sites. Within the Ae. aegypti, resistance ratios ranged from 3.5- to 30.0-fold when compared to the ORL1952 laboratory susceptible strain. Expression of several P450s was higher than in the ORL1952 strain, but the pattern was similar between the field strains of Ae. aegypti. Higher resistance ratios did correlate with increasing percentages of the dilocus knockdown resistance (kdr) genotype. In contrast, Ae. albopictus from the 4 locations all had very low resistance ratios (<4-fold) when compared to the same laboratory susceptible strain. Five years later, we performed additional collections and characterization from the most resistant location to assess the temporal persistence of this difference in resistance between the species. The same pattern of high resistance in Ae. aegypti and low resistance in sympatric Ae. albopictus remained 5 yr later and this may have implications for operational efficacy., (Published by Oxford University Press on behalf of Entomological Society of America 2023.)

Aedes aegypti (L.) is an important mosquito vector of emerging arboviruses such as Zika, dengue, yellow fever, and chikungunya. To quell potential disease outbreaks, its populations are controlled by applying pyrethroid insecticides, which selection pressure may lead to the development of insecticide resistance. Target site insensitivity to pyrethroids caused by non-synonymous knockdown resistance (kdr) mutations in the voltage-gated sodium (NaV) channel is a predominant mechanism of resistance in mosquitoes. To evaluate the potential impact of pyrethroid resistance on vector control, Ae. aegypti eggs were collected from eight mosquito control operational areas in Harris County, Texas, and emerged females were treated in field tests at four different distances from the pyrethroid Permanone 31-66 source. The females were genotyped by melting curve analyses to detect two kdr mutations (V1016I and F1534C) in the NaV channel. Harris County females had higher survivorship rates at each distance than the pyrethroid-susceptible Orlando strain females. Survivorship increased with distance from the pyrethroid source, with 39% of field-collected mosquitoes surviving at 7.62 m and 82.3% at 22.86 m from the treatment source. Both the V1016I and F1534C pyrethroid resistant genotypes were widely distributed and at high frequency, with 77% of the females being double homozygous resistant (II/CC), this being the first report of kdr mutations in Ae. aegypti in Harris County. Analysis of the probability of survival for each mutation site independently indicated that the CC genotype had similar probability of survival as the FC heterozygous, while the II genotype had higher survival than both the VI and VV, that did not differ. The double homozygous resistant genotype (II/CC) had the highest probability of survival. A linear model estimated probability of survival for areas and genotypes. The high frequency and widespread distribution of double-homozygote pyrethroid-resistant Ae. aegypti may jeopardize disease vector control efforts in Harris County., Competing Interests: The authors have declared that no competing interests exist.

Culex quinquefasciatus is one of the most important mosquito vectors of arboviruses. Currently, the fastest approach to control disease transmission is the application of synthetic adulticide insecticides. However, in highly populated urban centers the development of insecticide resistance in mosquito populations could impair insecticide efficacy and therefore, disease control. To assess the effect of resistance on vector control, females of Cx. quinquefasciatus collected from six mosquito control operational areas in Harris County, Texas, were treated in field cage tests at three different distances with the pyrethroid Permanone® 31-66 applied at the operational rate. Females were analyzed by sequencing and/or diagnostic PCR using de novo designed primers for detecting the kdr-like mutation in the voltage-gated sodium channel (L982F; TTA to TTT) (house fly kdr canonical mutation L1014F). Females from the Cx. quinquefasciatus susceptible Sebring strain and those from the six operational areas placed at 30.4 m from the treatment source were killed in the tests, while 14% of field-collected mosquitoes survived at 60.8 m, and 35% at 91.2 m from the source. The diagnostic PCR had a with 97.5% accuracy to detect the kdr-like mutation. Pyrethroid resistant mosquitoes carrying the L982F mutation were broadly distributed in Harris County at high frequency. Among mosquitoes analyzed (n = 1,028), the kdr-kdr genotype was prevalent (81.2%), the kdr-s genotype was 18%, and s-s mosquitoes were less than 1% (n = 8). A logistic regression model estimated an equal probability of survival for the genotypes kdr-kdr and kdr-s in all areas analyzed. Altogether, our results point to a high-risk situation for the pyrethroid-based arboviral disease control in Harris County., Competing Interests: The authors have declared that no competing interests exist.

Mosquito-borne pathogens contribute significantly to the global burden of infectious diseases and are a continuing public health concern in the United States. Blood feeding by vector mosquitoes is a critical step in the transmission of human pathogens. Continuous surveillance of mosquito feeding patterns, especially in major population centers, is necessary for sustainable, effective control strategies. To better understand female feeding habits in Harris County, TX, we trapped mosquitoes from various locations, distributed among urban and semi-urban environments. Bloodmeal hosts were determined using a cytochrome C oxidase I DNA barcoding strategy. We identified a diverse array of vertebrate hosts with a high degree of avian host utilization, most surprisingly from anthropophilic species like Aedes aegypti (L.). We also detected sequences from two different vertebrate hosts in about half of specimens examined, suggesting that multiple bloodmeals had been acquired in the same feeding cycle by a sizable fraction of females in both urban and semi-urban locations. The high proportion of feeding on domestic chickens may indicate that a significant number of homeowners are rearing chickens within close proximity to study trap sites. As non-amplifying hosts, chickens may have a diluting effect on West Nile virus, as well as a zooprophylactic effect in their immediate vicinities. Ultimately, spatial and temporal host utilization patterns add insight into potential disease transmission dynamics, thereby informing vector control strategies in Harris County and other metropolitan areas., (© The Author(s) 2020. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The Asian tiger mosquito, Aedes albopictus, is an anthropophilic aggressive daytime-biting nuisance and an efficient vector of certain arboviruses and filarial nematodes. Over the last 30 years, this species has spread rapidly through human travel and commerce from its native tropical forests of Asia to every continent except Antarctica. In 2011, a population of Asian tiger mosquito (Aedes albopictus) was discovered in Los Angeles (LA) County, California. To determine the probable origin of this invasive species, the genetic structure of the population was compared against 11 populations from the United States and abroad, as well as preserved specimens from a 2001 introduction into California using the mitochondrial cytochrome c oxidase 1 (CO1) gene. A total of 66 haplotypes were detected among samples and were divided into three main groups. Aedes albopictus collected in 2001 and 2011 from LA County were genetically related and similar to those from Asia but distinct from those collected in the eastern and southeastern United States. In view of the high genetic similarities between the 2001 and 2011 LA samples, it is possible that the 2011 population represents in part the descendants of the 2001 introduction. There remains an imperative need for improved surveillance and control strategies for this species.