A Tribute to Bill Black: Breakthroughs in Mosquito Vector Competence and Insecticide Resistance Research

A special issue of Insects (ISSN 2075-4450).

Deadline for manuscript submissions: closed (31 March 2021) | Viewed by 35830

Special Issue Editors


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Guest Editor
Department of Microbiology, Immunology and Pathology, Colorado State University, Campus Delivery 1690, Fort Collins, CO 80523, USA
Interests: vector biology; arboviruses; mosquito anti-viral responses; molecular biology; mosquito immunity; genomic regulatory regions
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Guest Editor
Department of Microbiology, Immunology, and Pathology, Colorado State University, Campus Delivery 1690, Fort Collins, CO 80523, USA
Interests: insecticide resistance; Aedes aegypti; toxicology; population genetics

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Guest Editor
Department of Microbiology Immunology and Pathology, Arthropod-borne and Infectious Diseases Laboratory, Colorado State University, Fort Collins, CO 80523-1692, USA
Interests: medical entomology; emerging arboviruses; bat-borne viruses; disease ecology; vector competence; Rift Valley fever virus
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Mosquitoes vector a broad array of serious human and animal viral pathogens. Numerous complex interactions of the environment, vector, host, and virus influence the efficiency of arbovirus transmission. A variety of mechanisms may also contribute to strain-specific differences in insecticide resistance, though this area remains understudied. Prior to the advent of high throughput sequencing, the analysis of quantitative trait loci contributed to the identification of mosquito genes associated with vector competence or permethrin resistance phenotypes. Today, target-capture high throughput sequencing has become a very effective population genetics tool. For some arboviruses, gene-for-gene interactions between viruses and mosquitoes condition vector competence. In the context of vector control, increased insecticide use to protect the public has been hampered by a rise in resistance. Further study of the complex features of vector competence and insecticide resistance is still needed to recognize underlying mechanisms and reveal new targets for vector control or interruption of virus transmission.

We dedicate this issue to William C Black IV, our steadfast mentor, colleague and friend. Dr Black is a Professor at Colorado State University’s Arthropod-borne and Infectious Diseases Laboratory in Fort Collins, Colorado, where he has served the medical entomology community for over 34 years through teaching, mentorship, and pioneering research linking vector genetics to phenotypes relevant to the transmission and control of arboviruses. Dr Black’s contribution to vector biology has covered topics as diverse as insecticide resistance, population genetics, tick biology and the genetics of vector competence to flaviviruses. He has co-authored over 200 publications (h=75), with major contributions spanning the generation of an improved reference genome for Aedes aegypti, the phylogeny and population genetics of hard and soft ticks, the development of population genetics tools for study of mosquitoes, ticks, aphids, and other insects, applying quantitative genetics to the study of virus transmission and insecticide resistance phenotypes in mosquitoes, and elucidating the global genetic structure of Aedes aegypti mosquito populations. True to his breadth of interests and the diverse subject matter for which he is recognized, this special issue, “A Tribute to Bill Black: breakthroughs in mosquito vector competence and insecticide resistance research ”, will report an assorted blend of breakthroughs in the understanding of the genetics of insecticide resistance, as well as studies on vector ecology, genetics, genomics, and arbovirus transmission. We welcome submission of previously unpublished manuscripts of original works or reviews that advance the field medical entomology. We will also consider diverse articles that are demonstrative of Dr. Black’s legacy in the medical entomology field.

Dr. Corey L. Campbell
Dr. Karla Saavedra-Rodriguez
Dr. Rebekah C. Kading
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • insecticide resistance
  • Aedes aegypti
  • vector competence
  • Rift Valley fever virus
  • dengue virus
  • flavivirus
  • Culex
  • toxicology

Published Papers (11 papers)

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Research

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14 pages, 272 KiB  
Article
The Taxonomic History of Ochlerotatus Lynch Arribálzaga, 1891 (Diptera: Culicidae)
by Lílian Ferreira de Freitas and Lyric C. Bartholomay
Insects 2021, 12(5), 452; https://doi.org/10.3390/insects12050452 - 14 May 2021
Cited by 4 | Viewed by 1660
Abstract
A review of all taxonomic actions within the subgenus Ochlerotatus Lynch Arribálzaga, 1891 (Diptera: Culicidae) sensu Reinert et al. (2008) is provided. In particular, the complex historical taxonomic treatment of the type species of this group is dissected and explained in detail. Additionally, [...] Read more.
A review of all taxonomic actions within the subgenus Ochlerotatus Lynch Arribálzaga, 1891 (Diptera: Culicidae) sensu Reinert et al. (2008) is provided. In particular, the complex historical taxonomic treatment of the type species of this group is dissected and explained in detail. Additionally, current challenges with the definition of the subgenus and its constituents are discussed, as are the requisite steps for a successful revision of the taxon. Going forward, we conclude that a taxonomic revision of the species should include a neotype designation for Ochlerotatus scapularis (Rondani, 1848) from topotypical material. Additionally, we provide a review of the characters and taxa that need to be re-evaluated and well-described in order to stabilize the taxonomy of the subgenus. This effort represents a key step towards a stable nomenclature of the Tribe Aedini. Full article
18 pages, 10382 KiB  
Article
Nootkatone Is an Effective Repellent against Aedes aegypti and Aedes albopictus
by Taylor C. Clarkson, Ashley J. Janich, Irma Sanchez-Vargas, Erin D. Markle, Megan Gray, John R. Foster, William C. Black IV, Brian D. Foy and Ken E. Olson
Insects 2021, 12(5), 386; https://doi.org/10.3390/insects12050386 - 27 Apr 2021
Cited by 11 | Viewed by 3559
Abstract
We tested a nootkatone product for insecticide activity against the most prominent vectors of Zika virus (ZIKV), Aedes aegypti, and Aedes albopictus. We tested the permethrin-resistant (PERM-R) Vergel strain of A. aegypti and the permethrin-susceptible (PERM-S) New Orleans strain of A. aegypti [...] Read more.
We tested a nootkatone product for insecticide activity against the most prominent vectors of Zika virus (ZIKV), Aedes aegypti, and Aedes albopictus. We tested the permethrin-resistant (PERM-R) Vergel strain of A. aegypti and the permethrin-susceptible (PERM-S) New Orleans strain of A. aegypti to determine if insecticide resistance affected their susceptibility to nootkatone. Bottle bioassays showed that the PERM-S strain (New Orleans) was more susceptible to nootkatone than the confirmed A. aegypti permethrin-resistant (PERM-R) strain, Vergel. The A. albopictus strain ATM-NJ95 was a known PERM-S strain and Coatzacoalcos permethrin susceptibility was unknown but proved to be similar to the ATM-NJ95 PERM-S phenotype. The A. albopictus strains (ATM-NJ95 and Coatzacoalcos) were as susceptible to nootkatone as the New Orleans strain. Bottle bioassays conducted with ZIKV-infected mosquitoes showed that the New Orleans (PERM-S) strain was as susceptible to nootkatone as the mock-infected controls, but the PERM-R strain was less susceptible to nootkatone than the mock-infected controls. Repellency/irritancy and biting inhibition bioassays (RIBB) of A. aegypti determined whether the nootkatone-treated arms of three human subjects prevented uninfected A. aegypti mosquitoes from being attracted to the test subjects and blood-feeding on them. The RIBB analyses data calculated the spatial activity index (SAI) and biting inhibition factor (BI) of A. aegypti at different nootkatone concentrations and then compared the SAI and BI of existing repellency products. We concluded that nootkatone repelled mosquitoes at a rate comparable to 7% DEET or 5% picaridin and has the potential to be an efficacious repellent against adult A. aegypti mosquitoes. Full article
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15 pages, 1382 KiB  
Article
Characterizing and Quantifying Arbovirus Transmission by Aedes aegypti Using Forced Salivation and Analysis of Bloodmeals
by Megan R. Miller, Madeleine R. Sorensen, Erin D. Markle, Taylor C. Clarkson, Ashley L. Knight, Michelle J. Savran and Brian D. Foy
Insects 2021, 12(4), 304; https://doi.org/10.3390/insects12040304 - 30 Mar 2021
Cited by 6 | Viewed by 2804
Abstract
Arbovirus transmission studies are dependent on the ability to estimate the titer of virus transmitted from infectious mosquitoes to a host. There are several methods for estimating virus titer in mosquito saliva, including (1) using forced salivation (FS) whereby the infectious mosquito’s proboscis [...] Read more.
Arbovirus transmission studies are dependent on the ability to estimate the titer of virus transmitted from infectious mosquitoes to a host. There are several methods for estimating virus titer in mosquito saliva, including (1) using forced salivation (FS) whereby the infectious mosquito’s proboscis is forced into a capillary tube containing media to collect and test their saliva for virus, and (2) by quantifying virus expectorated into host tissues or into the blood contained in an artificial feeder immediately after blood feeding. We studied FS and bloodmeals to estimate and compare titers of Zika virus and chikungunya virus transmitted by the mosquito vector Aedes aegypti. Infectious virus and viral genomes of both viruses were detected more often from individual mosquitoes using immersion oil for the FS media compared to fetal bovine serum (FBS) plus glycerol, but the FS media had no influence on virus quantification from positive samples. FS virus titers were equivalent when comparing individuals or groups of mosquitoes that never received a blood meal compared to those that were blood fed immediately prior, showing that blood feeding does not influence FS. This suggested that performing FS on mosquitoes after blood feeding might be an efficient way to estimate virus transmitted during blood feeding. However, detecting virus from the blood remaining in an artificial feeder post-blood feeding was mostly unsuccessful relative to quantifying virus from FS of the post-blood fed mosquitoes. In contrast, immunocompromised mice always became infected after being fed on by Zika-infected mosquitoes, even when no infectious virus was detected in their saliva by FS post-blood feed. Due to this discrepancy, we tested the ingested bloodmeals of individual mosquitoes that fed on artificial blood feeders for virus, and compared these to virus in their saliva harvested from FS and to virus in their bodies. These experiments revealed ~50–100 times higher virus titers in the dissected bloodmeals compared to those detected in the same mosquitoes’ saliva, demonstrating how mosquitoes re-ingest much of their saliva during artificial blood feeding, and highlighting a large increase in virus transmission during Aedes aegypti blood feeding. Both FS and the dissected bloodmeals of artificially blood-fed mosquitoes showed that the quantity of viral RNA expectorated by mosquitoes was 2–5 logs more than the quantity of infectious virus. The results from this study add critical information to understanding and quantifying the transmission of Aedes aegypti arboviruses. Full article
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14 pages, 2316 KiB  
Article
A Method for Repeated, Longitudinal Sampling of Individual Aedes aegypti for Transmission Potential of Arboviruses
by E. Handly Mayton, Heather M. Hernandez, Christopher J. Vitek and Rebecca C. Christofferson
Insects 2021, 12(4), 292; https://doi.org/10.3390/insects12040292 - 27 Mar 2021
Cited by 6 | Viewed by 3603
Abstract
Mosquito-borne viruses are the cause of significant morbidity and mortality worldwide, especially in low- and middle-income countries. Assessing risk for viral transmission often involves characterization of the vector competence of vector–virus pairings. The most common determination of vector competence uses discreet, terminal time [...] Read more.
Mosquito-borne viruses are the cause of significant morbidity and mortality worldwide, especially in low- and middle-income countries. Assessing risk for viral transmission often involves characterization of the vector competence of vector–virus pairings. The most common determination of vector competence uses discreet, terminal time points, which cannot be used to investigate variation in transmission aspects, such as biting behavior, over time. Here, we present a novel method to longitudinally measure individual biting behavior and Zika virus (ZIKV) transmission. Individual mosquitoes were exposed to ZIKV, and from 9 to 24 days post-exposure, individuals were each offered a 180 μL bloodmeal every other day. Biting behavior was observed and characterized as either active probing, feeding, or no bite. The bloodmeal was then collected, spun down, serum collected, and tested for ZIKV RNA via qRT-PCR to determine individuals’ vector competence over time. This included whether transmission to the bloodmeal was successful and the titer of expectorated virus. Additionally, serum was inoculated onto Vero cells in order to determine infectiousness of positive recovered sera. Results demonstrate heterogeneity in not only biting patterns but expectorated viral titers among individual mosquitoes over time. These findings demonstrate that the act of transmission is a complex process governed by mosquito behavior and mosquito–virus interaction, and herein we offer a method to investigate this phenomenon. Full article
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13 pages, 1270 KiB  
Article
Phylogenetic Complexity of Morphologically Identified Anopheles squamosus in Southern Zambia
by Jordan E. Hoffman, Ilinca I. Ciubotariu, Limonty Simubali, Twig Mudenda, William J. Moss, Giovanna Carpi, Douglas E. Norris, Jennifer C. Stevenson and on behalf of Southern and Central Africa International Centers of Excellence for Malaria Research
Insects 2021, 12(2), 146; https://doi.org/10.3390/insects12020146 - 8 Feb 2021
Cited by 10 | Viewed by 2815
Abstract
Despite dramatic reductions in malaria cases in the catchment area of Macha Hospital, Choma District, Southern Province in Zambia, prevalence has remained near 1–2% by RDT for the past several years. To investigate residual malaria transmission in the area, this study focuses on [...] Read more.
Despite dramatic reductions in malaria cases in the catchment area of Macha Hospital, Choma District, Southern Province in Zambia, prevalence has remained near 1–2% by RDT for the past several years. To investigate residual malaria transmission in the area, this study focuses on the relative abundance, foraging behavior, and phylogenetic relationships of Anopheles squamosus specimens. In 2011, higher than expected rates of anthropophily were observed among “zoophilic” An. squamosus, a species that had sporadically been found to contain Plasmodium falciparum sporozoites. The importance of An. squamosus in the region was reaffirmed in 2016 when P. falciparum sporozoites were detected in numerous An. squamosus specimens. This study analyzed Centers for Disease Control (CDC) light trap collections of adult mosquitoes from two collection schemes: one performed as part of a reactive-test-and-treat program and the second performed along a geographical transect. Morphological identification, molecular verification of anopheline species, and blood meal source were determined on individual samples. Data from these collections supported earlier studies demonstrating An. squamosus to be primarily exophagic and zoophilic, allowing them to evade current control measures. The phylogenetic relationships generated from the specimens in this study illustrate the existence of well supported clade structure among An. squamosus specimens, which further emphasizes the importance of molecular identification of vectors. The primarily exophagic behavior of An. squamosus in these collections also highlights that indoor vector control strategies will not be sufficient for elimination of malaria in southern Zambia. Full article
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12 pages, 922 KiB  
Article
Effect of Selection for Pyrethroid Resistance on Abiotic Stress Tolerance in Aedes aegypti from Merida, Yucatan, Mexico
by Keenan Amer, Karla Saavedra-Rodriguez, William C. Black IV and Emilie M. Gray
Insects 2021, 12(2), 124; https://doi.org/10.3390/insects12020124 - 31 Jan 2021
Cited by 2 | Viewed by 1892
Abstract
The study of fitness costs of insecticide resistance mutations in Aedes aegypti has generally been focused on life history parameters such as fecundity, mortality, and energy reserves. In this study we sought to investigate whether trade-offs might also exist between insecticide resistance and [...] Read more.
The study of fitness costs of insecticide resistance mutations in Aedes aegypti has generally been focused on life history parameters such as fecundity, mortality, and energy reserves. In this study we sought to investigate whether trade-offs might also exist between insecticide resistance and other abiotic stress resistance parameters. We evaluated the effects of the selection for permethrin resistance specifically on larval salinity and thermal tolerance. A population of A. aegypti originally from Southern Mexico was split into two strains, one selected for permethrin resistance and the other not. Larvae were reared at different salinities, and the fourth instar larvae were subjected to acute thermal stress; then, survival to both stresses was compared between strains. Contrary to our predictions, we found that insecticide resistance correlated with significantly enhanced larval thermotolerance. We found no clear difference in salinity tolerance between strains. This result suggests that insecticide resistance does not necessarily carry trade-offs in all traits affecting fitness and that successful insecticide resistance management strategies must account for genetic associations between insecticide resistance and abiotic stress resistance, as well as traditional life history parameters. Full article
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22 pages, 2368 KiB  
Article
The Genetic Basis for Salivary Gland Barriers to Arboviral Transmission
by Irma Sanchez-Vargas, Ken E. Olson and William C. Black
Insects 2021, 12(1), 73; https://doi.org/10.3390/insects12010073 - 15 Jan 2021
Cited by 19 | Viewed by 3629
Abstract
Arthropod-borne viruses (arboviruses) infect mosquito salivary glands and then escape to saliva prior to virus transmission. Arbovirus transmission from mosquitoes can be modulated by salivary gland infection barriers (SGIBs) and salivary gland escape barriers (SGEBs). We determined the influence of SGIBs and SGEBs [...] Read more.
Arthropod-borne viruses (arboviruses) infect mosquito salivary glands and then escape to saliva prior to virus transmission. Arbovirus transmission from mosquitoes can be modulated by salivary gland infection barriers (SGIBs) and salivary gland escape barriers (SGEBs). We determined the influence of SGIBs and SGEBs by estimating the quantitative genetic contributions of Aedes aegypti half-sib families (Mapastepec, Mexico) infected with three dengue 2 (DENV2), two chikungunya (CHIKV), and two Zika (ZIKV) genotypes. We determined virus titer per salivary gland and saliva at seven days post-infection and virus prevalence in the half-sib population. CHIKV or ZIKV genotypes did not present SGIB, whereas DENV2 genotypes showed low rates of SGIB. However, virus titer and prevalence due to additive genetic factors in the half-sib family displayed a significant narrow-sense heritability (h2) for SGIB in two of the three DENV2 genotypes and one CHIKV and one ZIKV genotype. SGEBs were detected in all seven virus strains: 60–88% of DENV2 and 48–62% of CHIKV or ZIKV genotype infections. SGEB h2 was significant for all CHIKV or ZIKV genotypes but not for any of the DENV2 genotypes. SGIBs and SGEBs exhibited classical gene-by-gene interaction dynamics and are influenced by genetic factors in the mosquito and the virus. Full article
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13 pages, 1711 KiB  
Article
Evidence for Divergent Selection on Immune Genes between the African Malaria Vectors, Anopheles coluzzii and A. gambiae
by Yoosook Lee, Lattha Souvannaseng, Travis C. Collier, Bradley J. Main, Laura C. Norris, Abdarahamane Fofana, Sekou F. Traoré, Anthony J. Cornel, Shirley Luckhart and Gregory C. Lanzaro
Insects 2020, 11(12), 893; https://doi.org/10.3390/insects11120893 - 18 Dec 2020
Cited by 2 | Viewed by 2742
Abstract
During their life cycles, microbes infecting mosquitoes encounter components of the mosquito anti-microbial innate immune defenses. Many of these immune responses also mediate susceptibility to malaria parasite infection. In West Africa, the primary malaria vectors are Anopheles coluzzii and A. gambiae sensu stricto, [...] Read more.
During their life cycles, microbes infecting mosquitoes encounter components of the mosquito anti-microbial innate immune defenses. Many of these immune responses also mediate susceptibility to malaria parasite infection. In West Africa, the primary malaria vectors are Anopheles coluzzii and A. gambiae sensu stricto, which is subdivided into the Bamako and Savanna sub-taxa. Here, we performed whole genome comparisons of the three taxa as well as genotyping of 333 putatively functional SNPs located in 58 immune signaling genes. Genome data support significantly higher differentiation in immune genes compared with a randomly selected set of non-immune genes among the three taxa (permutation test p < 0.001). Among the 58 genes studied, the majority had one or more segregating mutations (72.9%) that were significantly diverged among the three taxa. Genes detected to be under selection include MAP2K4 and Raf. Despite the genome-wide distribution of immune genes, a high level of linkage disequilibrium (r2 > 0.8) was detected in over 27% of SNP pairs. We discuss the potential role of immune gene divergence as adaptations to the different larval habitats associated with A. gambiae taxa and as a potential force driving ecological speciation in this group of mosquitoes. Full article
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Review

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19 pages, 1131 KiB  
Review
From Global to Local—New Insights into Features of Pyrethroid Detoxification in Vector Mosquitoes
by William C. Black IV, Trey K. Snell, Karla Saavedra-Rodriguez, Rebekah C. Kading and Corey L. Campbell
Insects 2021, 12(4), 276; https://doi.org/10.3390/insects12040276 - 24 Mar 2021
Cited by 12 | Viewed by 4255
Abstract
The threat of mosquito-borne diseases continues to be a problem for public health in subtropical and tropical regions of the world; in response, there has been increased use of adulticidal insecticides, such as pyrethroids, in human habitation areas over the last thirty years. [...] Read more.
The threat of mosquito-borne diseases continues to be a problem for public health in subtropical and tropical regions of the world; in response, there has been increased use of adulticidal insecticides, such as pyrethroids, in human habitation areas over the last thirty years. As a result, the prevalence of pyrethroid-resistant genetic markers in natural mosquito populations has increased at an alarming rate. This review details recent advances in the understanding of specific mechanisms associated with pyrethroid resistance, with emphasis on features of insecticide detoxification and the interdependence of multiple cellular pathways. Together, these advances add important context to the understanding of the processes that are selected in resistant mosquitoes. Specifically, before pyrethroids bind to their targets on motoneurons, they must first permeate the outer cuticle and diffuse to inner tissues. Resistant mosquitoes have evolved detoxification mechanisms that rely on cytochrome P450s (CYP), esterases, carboxyesterases, and other oxidation/reduction (redox) components to effectively detoxify pyrethroids to nontoxic breakdown products that are then excreted. Enhanced resistance mechanisms have evolved to include alteration of gene copy number, transcriptional and post-transcriptional regulation of gene expression, as well as changes to cellular signaling mechanisms. Here, we outline the variety of ways in which detoxification has been selected in various mosquito populations, as well as key gene categories involved. Pathways associated with potential new genes of interest are proposed. Consideration of multiple cellular pathways could provide opportunities for development of new insecticides. Full article
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27 pages, 905 KiB  
Review
Modernizing the Toolkit for Arthropod Bloodmeal Identification
by Erin M. Borland and Rebekah C. Kading
Insects 2021, 12(1), 37; https://doi.org/10.3390/insects12010037 - 6 Jan 2021
Cited by 18 | Viewed by 4831
Abstract
Understanding vertebrate–vector interactions is vitally important for understanding the transmission dynamics of arthropod-vectored pathogens and depends on the ability to accurately identify the vertebrate source of blood-engorged arthropods in field collections using molecular methods. A decade ago, molecular techniques being applied to arthropod [...] Read more.
Understanding vertebrate–vector interactions is vitally important for understanding the transmission dynamics of arthropod-vectored pathogens and depends on the ability to accurately identify the vertebrate source of blood-engorged arthropods in field collections using molecular methods. A decade ago, molecular techniques being applied to arthropod blood meal identification were thoroughly reviewed, but there have been significant advancements in the techniques and technologies available since that time. This review highlights the available diagnostic markers in mitochondrial and nuclear DNA and discusses their benefits and shortcomings for use in molecular identification assays. Advances in real-time PCR, high resolution melting analysis, digital PCR, next generation sequencing, microsphere assays, mass spectrometry, and stable isotope analysis each offer novel approaches and advantages to bloodmeal analysis that have gained traction in the field. New, field-forward technologies and platforms have also come into use that offer promising solutions for point-of-care and remote field deployment for rapid bloodmeal source identification. Some of the lessons learned over the last decade, particularly in the fields of DNA barcoding and sequence analysis, are discussed. Though many advancements have been made, technical challenges remain concerning the prevention of sample degradation both by the arthropod before the sample has been obtained and during storage. This review provides a roadmap and guide for those considering modern techniques for arthropod bloodmeal identification and reviews how advances in molecular technology over the past decade have been applied in this unique biomedical context. Full article
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Other

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5 pages, 426 KiB  
Brief Report
Susceptibility of South Texas Aedes aegypti to Pyriproxyfen
by Jose G. Juarez, Selene M. Garcia-Luna, Christopher M. Roundy, Alyssa Branca, Michael G. Banfield and Gabriel L. Hamer
Insects 2021, 12(5), 460; https://doi.org/10.3390/insects12050460 - 17 May 2021
Cited by 1 | Viewed by 2017
Abstract
An integral part to integrated mosquito management is to ensure chemical products used for area-wide control are effective against a susceptible population of mosquitoes. Prior to conducting an intervention trial using an insect growth regulator, pyriproxyfen, in South Texas to control Aedes aegypti [...] Read more.
An integral part to integrated mosquito management is to ensure chemical products used for area-wide control are effective against a susceptible population of mosquitoes. Prior to conducting an intervention trial using an insect growth regulator, pyriproxyfen, in South Texas to control Aedes aegypti, we conducted a larval bioassay to evaluate baseline levels of susceptibility. We used seven serially-diluted doses ranging from 2.5 ppb to 6.3 × 10−4 ppb. We observed 100% inhibition emergence (IE) at even the lowest dose of 6.3 × 10−4 ppb in our susceptible reference colony of Ae. aegypti Liverpool. In our field strain of Ae. aegypti (F5 colonized from South Texas) we observed 79.8% IE at 6.3 × 10−4 ppb, 17.7% IE at 1.25 × 10−3 ppb, 98.7% IE at 1.25 × 10−2 ppb, and 100% emergence inhibition for the remainder of the doses. Given that commercial pyriproxyfen products are labeled for doses ranging to 50 ppb, we conclude that the field population sampled by this study are susceptible to this insect growth regulator. Full article
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