BackgroundAedes aegypti is associated with dengue, yellow fever, chikungunya and Zika viruses. This vector is widespread in tropical and subtropical areas, and can also occur in temperate areas at higher latitudes. The geographical distribution of Ae. aegypti continues to spread due to human activities. This is the first study to examine the population genetic structure of this insect in El Salvador, Central America.MethodsAedes aegypti larvae were collected from six geographical regions of El Salvador: Sonsonate, San Salvador, Chalatenango, Usulután, San Miguel and Morazán. Larvae were raised into adults, identified and preserved. Two molecular markers, amplified fragment length polymorphism (AFLP) genotyping and mitochondrial DNA (mtDNA) cytochrome c oxidase subunit 1 (cox1) sequencing, were used to investigate population genetic structure.ResultsStructure analysis found two genetically distinct populations; one occurs predominantly in the north and west, and a mix of two populations occurs in the southeast of the country. Genetic distances ranged from 0.028 (2.8%) to 0.091 (9%), and an AMOVA analysis found 11% variation between populations. Mitochondrial DNA cox1 sequences produced a haplotype network which consisted of 3 haplogroups and 10 haplotypes. Haplogroup 1 had low haplotype and nucleotide diversity and was found in all six regions. Haplogroups 2 and 3 had higher haplotype and nucleotide diversity, and were less abundant; haplogroup 3 was found in only 3 of the six regions studied. Bottleneck tests were significant, suggesting that populations had undergone a recent bottleneck. A maximum likelihood tree, which combined samples from this study with available sequences in GenBank, suggested that two genetically divergent lineages had been introduced.ConclusionsRelatively high genetic diversity was found in Ae. aegypti in El Salvador. The mtDNA sequences clustered into two lineages, as found in previous studies. Samples in El Salvador may be introduced from regions in North and South America where past eradication was not complete. Future study of genotypes in surrounding countries would provide a more complete picture of the movement and potential source of introductions of this vector. The distribution of the lineages and haplogroups may further our understanding of the epidemiology of Ae. aegypti associated vector borne diseases.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3226-5) contains supplementary material, which is available to authorized users.

Stink bugs (Hemiptera: Pentatomidae) are an economically important group of insects that attack numerous crops in the central valley of California. Management of these pests using pheromones or biological control can be species specific, and proper identification of insect species is essential for effective management. The objective was to examine genetic variability in four species of stink bugs, which included Chinavia hilaris (Say) (= Acrosternum hilare) (Hemiptera: Pentatomidae) , Chlorochroa uhleri (Stål) (Hemiptera: Pentatomidae) , Chlorochroa sayi (Stål) (Hemiptera: Pentatomidae), and Thyanta pallidovirens (Stål) (Hemiptera: Pentatomidae) and to determine whether there may be cryptic species present. Stink bugs were collected in pistachios or on adjacent vegetation when abundant in the central valley of California. The mitochondrial DNA cytochrome oxidase I (COI) gene region (i.e., the barcode) was sequenced for each individual. Data were combined with available GenBank accessions for each species and used to construct a phylogenetic tree. Divergence between genera ranged from 11.2 to 15.7%, whereas divergence between the two Chlorochroa spp. was 4.6%. Genetic variation within Chinavia hilaris collections was up to 4.7%, which suggests the presence of a cryptic species. Genetic divergence was highest between individuals of Chinavia hilaris from the west coast and the east coast of the United States. In contrast, genetic variation within individuals of C. uhleri and Ch. sayi was less than 1%. Nine haplotypes were found for Chinavia hilaris, five for C. uhleri, three for Ch. sayi, and five for T. pallidovirens. The relevance of correct species identification and genetic diversity to stink bug management practices was discussed.

Environmental and socioeconomic risk factors associated with the incidence of human West Nile virus (WNV) cases were investigated in the Northern San Joaquin Valley region of California, a largely rural area. The study included human WNV cases from the years 2011 to 2015 in the three-county area of San Joaquin, Stanislaus, and Merced Counties, and used census tracts as the unit of analysis. Environmental factors included temperature, precipitation, and WNV-positive mosquito pools. Socioeconomic variables included age, housing age, housing foreclosures, median income, and ethnicity. Chi-square independence tests were used to examine whether each variable was associated with the incidence of WNV cases using data from the three counties combined. In addition, negative binomial regression revealed that the environmental factors of temperature and precipitation were the strongest predictors of the incidence of human WNV cases, while the socioeconomic factor of ethnicity was a significant predictor as well, and is a factor to consider in prevention efforts. Source reduction of mosquito breeding sites and targeted prevention and education remain key in reducing the risk associated with WNV.

Background Wolbachia bacteria are widely distributed throughout terrestrial arthropod species. These bacteria can manipulate reproduction and influence the vector competence of their hosts. Recently, Wolbachia have been integrated into vector control programmes for mosquito management. A number of supergroups and strains exist for Wolbachia, and they have yet to be characterized for many mosquito species. In this study, we examined Wolbachia prevalence and their phylogenetic relationship to other Wolbachia, using mosquitoes collected in Merced County in the Central Valley of California. Methods Adult mosquitoes were collected from 85 sites in Merced County, California in 2017 and 2018. Traditional and quantitative PCR were used to investigate the presence or absence and the density of Wolbachia, using Wolbachia-specific 16S rRNA and Wolbachia-surface protein (wsp) genes. The supergroup of Wolbachia was determined, and Multilocus Sequence Typing (MLST) by sequencing five housekeeping genes (coxA, gatB, ftsZ, hcpA and fbpA) was also used to determine Wolbachia supergroup as well as strain. Results Over 7100 mosquitoes of 12 species were collected: Aedesmelanimon, Ae. nigromaculis, Ae. vexans, Ae. aegypti, Culex pipiens, Cx. stigmatosoma, Cx. tarsalis, Anopheles franciscanus, An. freeborni, An. punctipennis, Culiseta incidens and Cs. inornata. Eight showed evidence of Wolbachia. To our knowledge, this study is the first to report detection of Wolbachia in five of these species (Ae. melanimon, Cx. stigmatosoma, Cx. tarsalis, Cs. incidens and Cs. inornata). Culex pipiens and Cx. stigmatosoma had a high frequency and density of Wolbachia infection, which grouped into supergroup B; Cs. inornata clustered with supergroup A. MLST comparisons identified Cx. pipiens and Cx. stigmatosoma as wPip strain type 9 supergroup B. Six species had moderate to low (< 14%) frequencies of Wolbachia. Four species were negative, Ae. nigromaculis, An. franciscanus, An. freeborni and Ae. aegypti. Conclusions New records of Wolbachia detection were found in mosquitoes from Merced County, California. Culex stigmatosoma and Cs. inornata were new records for Wolbachia supergroup B and A, respectively. Other species with Wolbachia occurred with low frequency and low density. Detection of Wolbachia in mosquitoes can be used to inform potential vector control applications. Future study of Wolbachia within Cx. stigmatosoma and Cs. inornata in California and through the range of these species could further explore Wolbachia infection in these two species.

25 Environmental and socioeconomic risk factors associated with West Nile Virus cases 26 were investigated in the Northern San Joaquin Valley region of California, a largely rural area. 27 The study included human West Nile Virus (WNV) cases from the years 2011-2015 in the three 28 county area of San Joaquin, Stanislaus and Merced Counties, and examined whether factors were 29 associated with WNV using census tracts as the unit of analysis. Environmental factors included 30 temperature, precipitation, mosquitoes positive for WNV, and habitat. Socioeconomic variables 31 included age, education, housing age, home vacancies, median income, population density, 32 ethnicity, and language spoken. Chi-squared independence tests were used to examine whether 33 each variable was associated with WNV in each county, and then also used for the three counties 34 combined. Logistic regression was used for a three-county combined analysis, to examine which 35 environmental and socioeconomic variables were most likely associated with WNV cases. The 36 chi-squared tests found that the variables associated with WNV varied in each of the three 37 counties. The chi-squared tests for data combined from the three counties found that WNV cases 38 were significantly associated with mosquitoes positive for WNV, urban habitat, higher home 39 vacancies, higher population density, higher education, and ethnicity. Logistic regression 40 analysis revealed that overall, the environmental factors precipitation, mean temperature, and 41 WNV positive mosquitoes were the strongest predictors of WNV cases. Results support efforts 42 of mosquito control districts, which aim for source reduction of mosquito breeding sites. In 43 addition, findings suggest that residents with higher income and education may be more aware of 44 WNV and its symptoms, and more likely to request testing from physicians. Lower income and 45 education residents may not be aware of WNV. Public health education might increase its 3 46 prevention messages about vector-borne disease in the various languages of the region, which 47 would contribute overall to public health in the region.