Doctoral candidate Lindsey Mack of the lab of medical entomologist-geneticist Geoffrey Attardo, associate professor, UC Davis Department of Entomology and Nematology,  is zeroing in on the yellow fever mosquito, Aedes aegypti, first detected in California in 2013. 

Infected Ae. aegypti mosquitoes can transmit dengue fever, chikungunya, Zika fever, Mayaro and yellow fever viruses, and other disease agents.

Mack will present her exit seminar on "Genetic and Molecular Factors Influencing Pyrethroid Response in Aedes aegypti from California" at 3:30 p.m., Tuesday, June 6 in 366 Briggs Hall. It also will be on Zoom. 

Mack studies Ae. aegypti with a focus on analysis of transcriptomic datasets and 3D imaging datasets. "Throughout my time in graduate school, my projects have considered pyrethroid resistance in Ae. aegypti; examining the genetic response to this insecticide. As I finish up my dissertation, I hope to pursue a career in industry using the skills I've developed to continue to analyze large datasets!"

Insecticide resistance is a global issue, Mack says in her exit seminar abstract. The mosquito was first colonized California in 2013 and arrived resistant to pyrethroids. "The pyrethroid target site genotype differs geographically in California and partially infers resistance phenotype, indicating that other mechanisms are at play as well."

Mack is the co-lead author (with doctoral candidate Erin Taylor Kelly of the Attardo lab) of  Frequency of Sodium Channel Genotypes and Association with Pyrethrum Knockdown Time in Populations of Californian Aedes aegypti, published in March 2021 in the journal Parasites and Vectors. The eight co-authors, in additioin to Attardo, included Anthony Cornel, Mosquito Control Research Laboratory, Kearney Agricultural Center, and Department of Entomology and Nematology. 

 "Since their detection in 2013, Aedes aegypti has become a widespread urban pest in California," the co-authors wrote in the abstract. "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."

"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."

The conclusion:

"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."

Mack,  who holds a bachelor of science degree (2018) in biology from Creighton University, Omaha, Neb.,  enrolled in the UC Davis graduate school program in 2018. 

Active in the Entomological Society of America, Mack scored second place in student competition at the 2022 joint meeting of the Entomological Societies of America, Canada, and British Columbia, held last November in Vancouver, British Columbia. She entered her presentation, "Three Dimensional Analysis of Vitellogenesis in Aedes aegypi Using Synchrotron X-Ray MicroCT,” in the category, "Graduate School Physiology, Biochemistry and Toxicology: Physiology.

Her abstract: "Traditional methods of viewing the internal anatomy of insects require some degree of tissue manipulation and/or destruction. Using synchrotron-based x-ray phase contrast microCT (pcMicroCT) avoids this issue and has the capability to produce high contrast, three dimensional images. Our lab is using this technique to study the morphological changes occurring in the mosquito Aedes aegypti during its reproductive cycle. Ae. aegypti is the primary global arbovirus vector, present on all continents except Antarctica. Their ability to spread these viruses is tightly linked with their ability to reproduce, as the production of eggs in this species is initiated by blood feeding. Amazingly, this species produces a full cohort of eggs (typically 50-100) in just 3 days' time following a blood meal. This rapid development represents dramatic shifts in physiological processes that result in massive volumetric changes to internal anatomy over time. To explore these changes thoroughly, a time course of microCT scans were completed over the vitellogenic period. This dataset provides a virtual representation of the volumetric, conformational, and positional changes occurring in tissues important for reproduction across the vitellogenic period. This dataset provides the field of vector biology with a detailed three-dimensional internal atlas of the processes of vitellogenesis in Ae. aegypti."

"As for career plans, I am applying to computational biology positions in industry," Mack said. "I'm not filing my dissertation until July so I am still working on this."

A highly controlled clinical study in Iquitos, Peru shows that a spatial repellent used as an intervention tool “significantly lowered the risk” of virus transmission by the yellow fever mosquito, Aedes aegypti, according to a team of 25 international scientists, including UC Distinguished Professor Thomas Scott and UC Davis project scientist Amy Morrison.  

The parallel, cluster-randomized, controlled trial revealed that a spatial repellent,  currently under review by the World Health Organization (WHO), reduced human Aedes-borne virus infection by 34.1 percent. 

“That is a significant statistical and public health reduction,” said Scott, an internationally recognized medical entomologist who retired from the UC Davis Department of Entomology and Nematology in 2015 but continues his scientific research on the ecology and epidemiology of dengue, a mosquito-borne viral infection transmitted mainly by A. aegypti. Dengue, one of the most rapidly increasing vector-borne infectious diseases, infects some 400 million people a year,  with 4 billion people at risk annually. 

The clinical study results mean that spatial repellents have “the potential to reduce a variety of vector-borne diseases, augment existing public health efforts, and can be an effective component in vector control intervention strategies,” Scott said. 

The newly published research, “Efficacy of a Spatial Repellent for Control of Aedes-borne Virus Transmission: A Cluster-Randomized Trial in Iquitos, Peru,” appears in the Proceedings of the National Academy of Sciences (PNAS). The Bill and Melinda Gates Foundation funded the research in a grant to the University of Notre Dame (UND). Medical entomologist Nicole Achee, a research professor at UND, served as the project leader.  

“We are thrilled by the results and public health impact of this trial,” said Scott, who began working on dengue research in Iquitos in September 1998. “Randomized control trials of Aedes-transmitted viruses are complicated and logistically difficult to carry out, which helps explain why so few have been completed even though the data they generate is desperately needed.” 

“To have shown a substantial public health impact at an endemic site, is rewarding,” said Scott, now a resident of Luck, Wis. “Our results provide valuable new data on mosquito control that will help to fill long-standing knowledge gaps and improve guidance for development of enhanced public health policy. Because literally billions of people around the globe are at risk of infection and disease from these viruses we are encouraged that results from our trial will contribute to improved health and well-being of so many people.” 

Epidemiologist Amy Morrison, a 1996-2018 project scientist with the UC Davis Department of Entomology and Nematology and now with the UC Davis School of Veterinary Medicine's Department of Pathology, Microbiology and Immunology, served as the lead author of the PNAS paper. “This trial was the most logistically challenging field project I've ever participated in,” she said.  “I led the field efforts in Iquitos, Peru where I have resided since 1998.  Our research team continued to amaze me; they had to replace more than 20,000 products in more than 2,000 houses every 15 days and managed  80 percent coverage of participating houses.  This type of vector control trial is very difficult to carry out so demonstrating protective efficacy is very gratifying.” 

Achee said the Peru study outcomes “are a critical component to achieving our goals for supporting a WHO policy endorsement for spatial repellents. The reduction in Aedes-borne virus infection in at-risk participants seen in trial results have fundamentally contributed to the WHO encouraging further consideration for the use of this product class in public health worldwide. This is a historical milestone that was led by the UC Davis implementing team and I am thrilled to have been part of the collaborative effort." 

Spatial repellents are “devices that contain volatile active ingredients that disperse in air,” the authors explained. “The active ingredients can repel mosquitoes from entering a treated space, inhibit attraction to human host cues, or disrupt mosquito biting and blood-feeding behavior and, thus, interfere with mosquito–human contact. Any of these outcomes reduce the probability of pathogen transmission.” 

In their study, the scientists quantified the impact of a transfluthrin-based spatial repellent on reducing human infection. The repellent is known as a fast-acting pyrethroid insecticide with low persistency.  “From 2,907 households across 26 clusters (13 clusters each in treatment and control arm), 1,578 participants were assessed for evidence of infection (i.e., seroconversion) by survival analysis. Incidence of acute disease was measured among 16,683 participants,” they wrote in their abstract. “Adult mosquito collections were conducted to compare Ae. aegypti abundance, blood-fed rate, and egg laying status through mixed-effect difference-in-difference analyses. The spatial repellent significantly reduced human Aedes-borne virus infection by 34.1%, which was a significant statistical and public health reduction. Aedes aegypti abundance and blood-fed rates, secondary outcomes, were significantly reduced by 28.6% and 12.4%, respectively.”

More than half of the world population is at risk for infection with viruses transmitted by Aedes mosquitoes, including include dengue, Zika, chikungunya, and yellow fever, the scientists wrote.

Vector interventions are needed for Aedes-borne viral (ABV) disease prevention “but their application is hindered by the lack of evidence proving they prevent infection or disease," they wrote. "Results from our ABV study will help guide public health authorities responsible for operational management and worldwide ABV disease control and incentivize new strategies for disease prevention.” 

 “The primary mosquito vector, Aedes aegypti, thrives in modern tropical urban environments. Despite decades of effort to control Ae. aegypti populations and prevent disease, the geographic range of illness and the viruses this mosquito transmits continue to expand,” they related. “Rigorously proven vector control interventions that measure protective efficacy against Aedes-borne viruses are limited to Wolbachia in a single trial in Indonesia and do not include any chemical interventions. Spatial repellents, a new option for efficient vector control, are designed to decrease human exposure to Aedes-borne viruses by releasing active ingredients into the air that disrupt mosquito–human contact and, thus, reduce the risk of human infection.” 

They noted that “Spatial repellents are increasingly being recognized as a flexible class of vector control products with positive public health applications that go beyond Aedes-borne viral diseases. For example, transfluthrin- and metofluthrin-based mosquito coils can reduce malaria. The same spatial repellent device used in the Iquitos trial reduced malaria infections in an Indonesia trial. Spatial repellents, therefore, have the potential to reduce a variety of vector-borne diseases, augment existing public health efforts, and can be an effective component in vector control intervention strategies.” 

The Iquitos trial is one of two trials recommended by WHO for assessing public health value and developing global health policy for the intervention class of spatial repellents. “Fully integrating vector control into Aedes-borne viral disease prevention programs requires quantitative guidance based on quantitative measures of the impact from each intervention component,” the authors wrote. “Ministries of Health, local to national governments, and nongovernmental organizations can use the Peru trial results as an evidence base for informed application of spatial repellents. Considering the growing public health threat from Aedes-borne viral disease, difficulties of developing vaccines against multiple viruses, and past poorly informed vector control failures, enhanced Aedes-borne viral disease prevention will benefit greatly from interventions, like the Peru trial, with proven public health value. 

Thomas Scott. Scott, a member of three WHO committees and one of the world's Highly Cited Researchers for the third consecutive year, co-chairs a Lancet Commission that focuses on how prevention of viruses transmitted by Aedes mosquitoes.  He served on the faculty of the Department of Entomology, University of Maryland, from 1983 to 1996 before joining the UC Davis entomology faculty as a professor of entomology and director of the Vector-Borne Disease Laboratory. Highly honored by his peers, Scott won the coveted Harry Hoogstraal Medal from the American Society of Tropical Medicine and Hygiene in 2018. He is a fellow of the American Society of Tropical Medicine and Hygiene, Entomological Society of America, and the American Association for the Advancement of Science.  He holds bachelor and master's degrees from Bowling Green (Ohio) State University and a doctorate in ecology in 1981 from Pennsylvania State University.

Amy Morrison. Morrison, who holds a doctorate in public health from Yale University, with a concentration in epidemiology of infectious diseases, and a master's degree in public health from UCLA, has served as the principal investigator, co-principal investigator and a collaborator on a number of federally funded grants. She specializes in the epidemiology of tropical vector-borne diseases, with an emphasis on (1) arthropod vector ecology and dengue virus transmission dynamics and (2) spatial and temporal analyses using Geographic Information Systems. 

As a project scientist, Morrison supervises multiple studies on A. aegypti and dengue virus transmission dynamics, including longitudinal cohort studies evaluating A. aegypti control interventions, and the role of human movement in dengue transmission dynamics in Iquitos, funded by National Institutes of Health, Military Infectious Disease Research Program and Bill and Melinda Gates Foundation. She is an active member of the American Mosquito Control Association, American Association for the Advancement of Science, Entomological Society of America, American Society of Tropical Medicine and Hygiene, and the Society of Vector Ecologists.

Nicole Achee. Achee is a research associate professor in the Department of Biological Sciences, UND, and holds a joint associate professor appointment in the Eck Institute for Global Health, UND. She worked as a medical entomologist in the international settings of Belize, Indonesia, Mexico, Nepal, Peru, South Korea, Suriname, Tanzania and Thailand. Her curriculum vitae includes principal investigator for large scale clinical trials in Peru and Indonesia. Both studies aimed “to generate evidence of the protective efficacy of spatial repellents for prevention of malaria and dengue human infections for use toward full World Health Organization public health policy recommendations,” she says on her website.  Achee holds a doctorate in medical entomology from the Uniformed Services University of the Health Science, Bethesda, Md.

In addition to the Bill and Melinda Gates Foundation, the Iquitos project drew support from the Defense Threat Reduction Agency, Military Infectious Disease Research Program and the U.S. National Institute of Allergy and Infectious Diseases.

Mosquito expert Sylvia Fischer of the University of Buenos Aires, Argentina, will target the yellow fever mosquito, Aedes aegypti, when she presents a UC Davis Department of Entomology and Nematology's virtual seminar on Wednesday, Jan. 12.

Fischer, a member of the Mosquito Research Group, Department of Ecology, Genetics and Evolution, will speak on "The Recent Expansion of Aedes aegypti Distribution: Are the Populations Adapting to Colder Climate Regions?" at 4:10 p.m., Pacific Time. The Zoom link is https://ucdavis.zoom.us/j/99515291076. 

She will be introduced by UC Davis doctoral student Erin Taylor Kelly of the laboratory of medical entomologist-geneticist Geoffrey Attardo.  

"The mosquito Aedes aegypti, vector of dengue and other arboviruses, has recently expanded its distribution towards colder climate regions," Fischer says in her abstract. "This might be favored by an adaptation of the populations to local conditions. We explore the larval tolerance to low temperatures and the photo period-induced embryonic diapause as possible mechanisms occurring in temperate Argentina."

"My main research interest is on mosquito ecology, and my current project aims to analyze the effects of environmental conditions (photo period, temperature, humidity) and resources (larval food) on the fitness of Aedes aegypti," she writes on ResearchGate. "I am also interested in human caused environmental change and its consequences on vector borne diseases."

Fischer recently co-authored a research paper on Behavior of Aedes albifasciatus (Diptera: Culicidae) larvae from eggs with different dormancy times and its relationship with parasitism by Strelkovimermis spiculatus (Nematoda: Mermithidae).

Kelly, seminar host, researches the A. aegypti in the Attardo lab. She won a first-place award at the Entomological Society of America meeting last November with her poster, “Metabolic Snapshot: Using Metabolomics to Compare Near-Wild and Colonized Aedes aegypti.” She competed in the Physiology, Biochemistry and Ecology Section.  (See https://bit.ly/3HJR0IF). 

Fischer's talk meshes with the work of the Geoffrey Attardo laboratory. In one of his research projects, Attardo investigates the threat of these invasive mosquitoes, which have gained a foothold and spread throughout the state, putting California at risk for Aedes-vectored diseases such as dengue, chikungunya, Zika and yellow fever. Attardo studies the prevalence and physiology of insecticide resistance in Californian populations and evaluates the use of genetic markers to predict insecticide resistance and to track movement of genetically independent populations of aegypti throughout the state. Attardo and his lab are also currently developing novel biochemically oriented methods of insecticide resistance quantification to identify compounds that mosquito abatement districts can use for monitoring, and to define the biochemical pathways required to maintain this problematic adaptation. 

The department's weekly seminars, held at 4:10 p.m. on Wednesdays, are coordinated by nematologist Shahid Siddique, who may be emailed at ssiddique@ucdavis.edu with any technical questions.

Talk about a full schedule!

Nematologist Shahid Siddique, assistant professor, UC Davis Department of Entomology and Nematology, not only excels at research, teaching and public service but he serves as the coordinator of the department's weekly seminars for the 2021-22 academic year. And he's the host for many of the speakers as well. 

Siddique, who holds a doctorate in agriculture and biotechnology from the University of Natural Resources and Life Sciences, Vienna, Austria, joined the UC Davis faculty in March 2019 (see news story), after serving as a research group leader for several years at the University of Bonn, Germany.

The fall quarter seminars just ended, and the winter quarter seminars will begin Jan. 5 and continue through March 9. They take place on Wednesdays at 4:10 p.m. in 122 Briggs Hall, located off Kleiber Hall Drive. The topics range from alfalfa weevil to the yellow-fever mosquito.

"Both in-person and virtual seminars will be broadcast via Zoom at https://ucdavis.zoom.us/j/99515291076,  Siddique announced today. They are open to all interested persons.

The schedule:

Jan. 5, 2022
Randa Jabbour, associate professor, agroecology, University of Wyoming
Virtual seminar
Title: "Interdisciplinary Collaborations in Pest Management Research--My Alfalfa Weevil Stories" 
Host: Ian Grettenberger, assistant professor, UC Davis Department of Entomology and Nematology

Jan. 12, 2022
Sylvia Fischer, Mosquito Study Group, Department of Ecology, Genetics and Evolution, Universidad de Buenos Aires
Virtual seminar
Title: "Recent Expansion of Aedes aegypti Distribution: Are the Populations Adapting to Colder Climate Regions?"
Host: Erin "Taylor" Kelly, doctoral student in the Geoffrey Attardo lab, UC Davis Department of Entomology and Nematology

Jan. 19, 2022
Megan Meuti, assistant professor, Department of Entomology, The Ohio State University
Virtual seminar
Title: "How Do Mosquitoes Correctly Interpret Environmental Signals into Complex Seasonal Responses?"
Host: Geoffrey Attardo, assistant professor, UC Davis Department of Entomology and Nematology

Jan. 26, 2022
Tobin Hammer, postdoctoral researcher, University of Texas, Austin (he will start as an assistant professor in UC Irvine's Ecology and Evolutionary Biology Department in January 2022)
In-person seminar
Title: "Diversity and Dynamism in Social Bee Microbiomes"
Host: Rachel Vannette, associate professor, UC Davis Department of Entomology and Nematology

Feb. 2, 2022 
Simon Niels Groen, assistant professor, Department of Nematology, UC Riverside  
In-person seminar 
Title: "Plant Toxins and the Evolution of Host-Parasite Interactions" 
Host: Shahid Siddique, assistant professor, UC Davis Department of Entomology and Nematology

Feb. 9, 2022
Vince D'Amico, research entomologist, Communities and Landscapes of the Urban Northwest, U.S. Department of Agriculture 
In-person seminar
Title: "Monitoring and Ecological Research in the Forests of the BosWash Megalopolis"  
Host: Geoffrey Attardo, assistant professor, UC Davis Department of Entomology and Nematology

Feb. 16, 2022
Michelle Heck, adjunct associate professor and research molecular biologist, Boyce Thompson Institute, Ithaca, N.Y.
Virtual seminar
Title: Topic to be announced (Her program uses a combination of molecular, genetic, and proteomics approaches to understand how insects transmit plant pathogens and how pathogens manipulate host plants to ensure replication and transmission. A second area of research is the development of new pest management tools to enhance cultural control and to provide new management strategies for insect vector-borne diseases in plants)
Host: Tiffany Lowe-Power, assistant professor, UC Davis Department of Plant Pathology

Feb. 23, 2022
Adam Steinbrenner, assistant professor, Department of Biology, University of Washington
In-person seminar
Title: "Plant Immune Recognition of Insect Herbivores" 
Host: Shahid Siddique, assistant professor, UC Davis Department of Entomology and Nematology

March 2, 2022
Erica Henry, postdoctoral scholar, conservation biology, North Carolina State University
In-person seminar
Title: "Insect Conservation in an Uncertain Future"
Host: Emily Meineke, assistant professor, UC Davis Department of Entomology and Nematology

March 9, 2022
Melissa Mitchum, professor, plant nematology, University of Georgia
Virtual seminar 
Title: "The Tricks Phytonematodes Use to Modulate Plant Development"
Host: Shahid Siddique, assistant professor, UC Davis Department of Entomology and Nematology

For any Zoom technical issues, Siddique may be reached at ssiddique@ucdavis.edu.