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Scholarly Works (7 results)

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UC Davis Electronic Theses and Dissertations (2023)

The world's foremost arboviral vector, Aedes aegypti, has recently been established in California, with detections in 28 of 58 counties as of 2023(Aedes Aegypti and Aedes Albopictus Mosquitoes, n.d.). This dissertation explores population dynamics within the state, and the biology of insecticide resistance mechanisms using populations derived from Greater Los Angeles, Fresno, and Tulare counties.In Chapter 1, we utilize genomic data to investigate the population dynamics of Ae. aegypti in California. We report evidence of multiple introductions into the state, with distinct genetic clusters identified. We investigate a specific hypothesis: that a population of Ae. aegypti detected in Exeter, CA, in 2014 was successfully eradicated, and the region was then reinvaded in 2017. We find evidence to support this hypothesis and posit that the region was reinvaded by a population from Southern California. This chapter also explores varying levels of resistance to pyrethroid insecticides, facilitated by mutations in the Voltage-Gated Sodium Channel (VGSC), a primary mechanism of resistance. Chapter 2 delves into a phenotypic comparison between the Rockefeller laboratory strain and wild California Ae. aegypti populations. By integrating lifespan, transcriptomic, and metabolomic data, we uncovered significant differences in metabolic pathways, particularly those related to oxidoreductase activity. Notably, we observed baseline differences in oxidative stress response, energy metabolism, and lipid profiles between the populations. Our findings suggest that larval nutrition and metabolic resistance to pyrethroids significantly impact mosquito physiology and longevity. Finally, Chapter 3 investigates metabolic shifts in response to pyrethroid (Deltamethrin) exposure in two Ae. aegypti populations with distinct genetic backgrounds collected from Los Angeles and the Central Valley. By examining metabolic changes in two near-wild populations, we identified significant alterations in amino acid, lipid, and nucleotide metabolism following exposure. This study highlights the rapidity and variability of metabolic responses to insecticides, underlining potential targets for novel synergists in mosquito control. Overall, this dissertation uses a diversity of tools to investigate the spread, genetic diversity, and insecticide resistance mechanisms in Ae. aegypti, with a focus on California's evolving situation. The findings advance our understanding of Ae. aegypti resistance biology, vector management, and suggest avenues for more targeted and effective mosquito control measures

 REFERENCES 1. Aedes aegypti and Aedes albopictus mosquitoes. (n.d.). Cdph.ca.gov. Retrieved November 2023, from https://www.cdph.ca.gov/Programs/CID/DCDC/pages/Aedes-aegypti-and-Aedes-albopictus-mosquitoes.aspx

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UC Davis Previously Published Works (2020)
the mosquito Aedes aegypti (Ae. aegypti) is an important vector of arboviruses, including Zika, Dengue, and Chikungunya. The dietary requirements of larval Ae. aegypti are not well understood and likely impact developmental and physiological parameters knowledge of which could be important for vector control. This study examines the effects nutrition has on growth and development of larval Ae. aegypti of laboratory-reared Rockefeller strain mosquitoes. mosquito larvae were split into five feeding groups with diets providing different ratios of protein and carbohydrates. Each group received autolyzed Brewer's yeast (AY - high-protein), and/or rice flour (RF-high-carbohydrate). The groups were monitored to record larval developmental times, adult sizes and nutritional stores. the 100% AY group failed to pupate, suggesting the AY alone is either lacking in critical nutrients or is toxic at higher concentrations. The 100% RF group resulted in the smallest adults that took the longest time to reach pupation. Of the remaining groups, the 25% AY/75% RF (Med-low) diet yielded adult mosquitoes with highest average weight, wing length, and lipid stores relative to the other diets. the dietary requirements for development, body size, and nutrient stores of Ae. aegypti mosquitoes appear to be dependent on a relatively low but essential proportion of dietary protein to carbohydrates to achieve optimal developmental outcomes.
    Cover page: Impacts of Dietary Nutritional Composition on Larval Development and Adult Body Composition in the Yellow Fever Mosquito (Aedes aegypti)
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    UC Davis Previously Published Works (2021)

    Background

    Since their detection in 2013, Aedes aegypti has become a widespread urban pest in California. The availability of cryptic larval breeding sites in residential areas and resistance to insecticides pose significant challenges to control efforts. Resistance to pyrethroids is largely attributed to mutations in the voltage gated sodium channels (VGSC), the pyrethroid site of action. However, past studies have indicated that VGSC mutations may not be entirely predictive of the observed resistance phenotype.

    Methods

    To investigate the frequencies of VGSC mutations and the relationship with pyrethroid insecticide resistance in California, we sampled Ae. aegypti from four locations in the Central Valley, and the Greater Los Angeles area. Mosquitoes from each location were subjected to an individual pyrethrum bottle bioassay to determine knockdown times. A subset of assayed mosquitoes from each location was then analyzed to determine the composition of 5 single nucleotide polymorphism (SNP) loci within the VGSC gene.

    Results

    The distribution of knockdown times for each of the five Californian populations sampled was non-parametric with potentially bimodal distributions. One group succumbs to insecticidal effects around 35-45 min and the second group lasts up to and beyond the termination of the assay (120+ min). We detected 5 polymorphic VGSC SNPs within the sampled California populations. One is potentially new and alternatively spliced (I915K), and four are documented and associated with resistance: F1534C, V1016I, V410L and S723T. The Central Valley populations (Clovis, Dinuba, Sanger and Kingsburg) are fairly homogenous with only 5% of the mosquitoes showing heterozygosity at any given position. In the Greater LA mosquitoes, 55% had at least one susceptible allele at any of the five SNP loci. The known resistance allele F1534C was detected in almost all sampled mosquitoes (99.4%). We also observe significant heterogeneity in the knockdown phenotypes of individuals with the identical VGSC haplotypes suggesting the presence of additional undefined resistance mechanisms.

    Conclusions

    Resistance associated VGSC SNPs are prevalent, particularly in the Central Valley. Interestingly, among mosquitoes carrying all 4 resistance associated SNPs, we observe significant heterogeneity in bottle bioassay profiles suggesting that other mechanisms are important to the individual resistance of Ae. aegypti in California.
      Cover page: Frequency of sodium channel genotypes and association with pyrethrum knockdown time in populations of Californian Aedes aegypti
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      UC Davis Previously Published Works (2020)
      Rapid and significant range expansion of both the Zika virus (ZIKV) and its Aedes vector species has resulted in the declaration of ZIKV as a global health threat. Successful transmission of ZIKV by its vector requires a complex series of interactions between these entities including the establishment, replication and dissemination of the virus within the mosquito. The metabolic conditions within the mosquito tissues play a critical role in mediating the crucial processes of viral infection and replication and represent targets for prevention of virus transmission. In this study, we carried out a comprehensive metabolomic phenotyping of ZIKV infected and uninfected Ae. albopictus by untargeted analysis of primary metabolites, lipids and biogenic amines. We performed a comparative metabolomic study of infection state with the aim of understanding the biochemical changes resulting from the interaction between the ZIKV and its vector. We have demonstrated that ZIKV infection results in changes to the cellular metabolic environment including a significant enrichment of inosine and pseudo-uridine (Ψ) levels which may be associated with RNA editing activity. In addition, infected mosquitoes demonstrate a hypoglycemic phenotype and show significant increases in the abundance of metabolites such as prostaglandin H2, leukotriene D4 and protoporphyrinogen IX which are associated with antiviral activity. These provide a basis for understanding the biochemical response to ZIKV infection and pathology in the vector. Future mechanistic studies targeting these ZIKV infection responsive metabolites and their associated biosynthetic pathways can provide inroads to identification of mosquito antiviral responses with infection blocking potential.
        Cover page: Zika Virus Infection Results in Biochemical Changes Associated With RNA Editing, Inflammatory and Antiviral Responses in Aedes albopictus
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        UC Davis Previously Published Works (2021)
        [This corrects the article DOI: 10.3389/fmicb.2020.559035.].
          Cover page: Corrigendum: Zika Virus Infection Results in Biochemical Changes Associated With RNA Editing, Inflammatory and Antiviral Responses in Aedes albopictus
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2020)

          Background:

          Since their detection in 2013, Aedes aegypti has become a widespread urban pest in California. The availability of cryptic larval breeding sites in residential areas and resistance to insecticides pose significant challenges to control efforts. Resistance to pyrethroids is largely attributed to mutations in the voltage gated sodium channels (VGSC), the pyrethroid site of action. However, past studies have indicated that VGSC mutations may not be entirely predictive of the observed resistance phenotype.

          Methods:

          To investigate the frequencies of VGSC mutations and the relationship with pyrethroid insecticide resistance in California, we sampled Ae. aegypti from four locations in the Central Valley, and the Greater Los Angeles area. Mosquitoes from each location were subjected to an individual pyrethrum bottle bioassay to determine knockdown times. A subset of assayed mosquitoes from each location was then analyzed to determine the composition of 8 single nucleotide polymorphism (SNP) loci within the VGSC gene.

          Results:

          The distribution of knockdown times for each of the five Californian populations sampled was non-parametric with bimodal distributions. One group succumbs to insecticidal effects around 35-45 minutes and the second group lasts up to and beyond the termination of the assay (120+ minutes). We detected 5 SNPs polymorphic within California populations. One is potentially new and alternatively spliced (I915K), and four are known and associated with resistance: F1534C, V1016I, V410L and S723T. The Central Valley populations (Clovis, Dinuba, Sanger and Kingsburg) are fairly homogenous with only 5% of the mosquitoes showing heterozygosity at any given position. In the Greater LA mosquitoes 55% had at least one susceptible allele at any of the five SNPs. The known resistance allele F1534C was detected in almost all sampled mosquitoes (99.4%). We observe significant heterogeneity in individuals with the same genotypes, confirming that the resistance SNPs alone cannot.

          Conclusions:

          Resistance associated VGSC SNPs are prevalent, particularly in the Central Valley. Interestingly, among mosquitoes with all 4 resistance associated SNPs, we observe heterogeneity in bottle bioassay profiles suggesting that other mechanisms are important to the individual resistance of Ae. aegypti in California.
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2023)
            Established populations of Aedes aegypti, a mosquito vector of multiple major arthropod-borne viruses, were first found in three California (CA) cities in 2013. From 2013 to April 2021, Ae. aegypti thwarted almost all control efforts to stop its spread and expanded its range to 308 cities, including Exeter, in 22 counties in CA. Population genomic analyses have suggested that multiple genetically distinct Ae. aegypti populations were introduced into CA. However Ae. aegypti collected for the first time in 2014 in Exeter, appeared to be different from three major genetic clusters found elsewhere in CA. Due to intense control efforts by the Delta Vector Control District (DVCD), Ae. aegypti was thought to have been eliminated from Exeter in 2015. Unfortunately, it was recollected in 2018. It was not clear if the reemergence of Ae. aegypti in Exeter was derived from the bottlenecked remnants of the original 2014 Exeter population or from an independent invasion from a different population derived from surrounding areas. The goal of this work was to determine which of these scenarios occurred (recovery after bottleneck or reintroduction after elimination) and if elimination and reintroduction occurred to identify the origin of the invading population using a population genomic approach. Our results support the reintroduction after elimination hypothesis. The source of reintroduction, however, was unexpectedly from the southern CA cluster rather than from other two geographically closer central CA genetic clusters. We also conducted a knockdown resistance mutation profile, which showed Exeter 2014 had the lowest level of resistant alleles compared to the other populations, could have contributed towards DVCD’s ability to locally eliminate Ae. aegypti in 2014.
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