Research in Bill Walton's Laboratory

Research and Publications:  I am an aquatic entomologist and ecologist who works mostly in natural and man-made wetlands.  Currently, the research in my laboratory has three foci: wetlands ecology with an emphasis on mosquitoes, control of invasive Aedes mosquitoes in tank bromeliads and the development of autodissemination stations for underground storm drain system in the Coachella Valley.  The lab maintains interests in the bionomics of the tule mosquito, Culex erythrothorax, and the semiochemicals associated with larvivorous fishes.  We recently wrapped up a long-term collaboration on bacteria used as an environmentally friendly method for controlling mosquitoes.  Links to recent publications can be found either in the links in the paragraphs below or in the list of publications link at the bottom of this section of the web page.

  

The major emphasis of the wetlands research in my laboratory group is to integrate studies of mosquito biology and ecology with the design of control methodologies for pestiferous and pathogen-transmitting mosquitoes in wetlands.  We have been studying the effects of design features and management strategies for multipurpose constructed treatment wetlands on mosquito production and water quality performance.  In addition to studying the relationship of nutrients and other water quality variables to mosquito populations, our studies have focused across the food web from the temporal and spatial dynamics of bacterial populations to studies on alternative larvivorous fishes to the mosquitofish (Gambusia affinis) and collaborative studies with USGS scientists on the relationship of aquatic insect production to bird usage of wetland habitats.  Our applied research on mosquito control in man-made wetlands has been complemented with basic research on the population dynamics of larval mosquito populations, the ecological stoichiometry of mosquitoes, the interaction of mosquitoes with natural enemies, and the influence of vegetation on the temporal and spatial distribution of mosquito larvae in wetlands.  More recently, we have been studying the efficacy of alternative emergent macrophytes for constructed treatment wetlands, the microbiomes of mosquitoes and their environments, and the genetic/genomic basis of host selection of mosquitoes.

 

Dr. Aviva Goldmann is the lead scientist on our work controlling invasive Aedes in tank bromeliads.  She recently completed a study of colonization of tank bromeliads in sites in western Los Angeles County.  She has been testing the efficacy, persistence and phytotoxicity of different control agents for bromeliads.  We are currently collaborating with the San Gabriel Valley Mosquito and Vector Control District and the Coachella Valley Mosquito and Vector Control District.  Our industry partners include MGK, Central Life Sciences, ISCA Technologies and Valent Biosciences.  In addition to the studies in western LA County, we are working on the Agricultural Experiment Station at UC Riverside.  The work is funded by the Pacific Southwest Center of Excellence in Vector-borne Diseases and the IR-4 Program.

 

Other recent foci of work in my laboratory have been (1) investigating the use of biorational agents as an environmentally friendly method of controlling mosquitoes inhabiting underground storm drain systems (USDS), (2) the development of alternative methods for the surveillance of mosquito vectors and the pathogens that they transmit and (3) identification of the semiochemicals released by potential predators of mosquitoes that are detected by egg-laying mosquitoes to alter oviposition behavior.

 

We have been working in USDS in the Coachella Valley investigating the persistence and efficacy of commercially available formulations of fungi that are used by organic farmers against a wide variety of insect pests. These same strains of insect-specific fungi are effective against Cx. quinquefasciatus, a mosquito commonly found in USDS and an important vector of the West Nile virus in urban and suburban areas of southern California. Our preliminary findings indicate that meaningful levels of infection can persist in USDS for a month or more, and infections were detected in bioassays for up to 11 weeks after application in the field.  This work has been supported by the Coachella Valley Mosquito and Vector Control District, the Mosquito Research Foundation and the USDA-NIFA through the Agricultural Experiment Station at U.C. Riverside.  We have been experimenting incorporating other mosquito control agents (e.g., insect growth regulators) into the stations.

 

Our work on methods for the enhanced surveillance of vectors and mosquito-borne pathogens has lead to the development of two gravid traps that, on average, collect 7-fold more mosquitoes than does the standard CDC gravid trap used routinely by vector control districts for vector surveillance.  Even more important is that the new gravid traps collect vector mosquitoes that are rarely collected by the standard gravid trap.  For example, during spring, one of the new gravid trap designs collected up to nearly 70-fold more Cx. tarsalis than did the standard gravid trap and, on some dates, collected Cx. tarsalis and Cx. stigmatosoma when the CDC gravid trap failed to do so.  We investigated the relative importance of various components of the trap for collecting Cx. quinquefasciatus, Cx. stigmatosoma and Cx. tarsalis.  While the standard CDC gravid trap is still a more portable and probably a more practical method of collecting mosquitoes in the Cx. pipiens/Cx. quinquefasciatus species group than are the new designs, our alternative gravid trap designs may enhance the detection of arbovirus presence in vectors early in the annual activity period of mosquitoes.  Intervention at this time is critical to preventing amplification of arbovirus infections that can decimate particular species of wildlife and can spill over into humans and companion animals. A manuscript describing the two most effective designs will appear soon.

 

We found in both the laboratory and field that water containing chemicals released by fish used as biological control agents against mosquitoes can be detected by egg-laying females of some mosquitoes.  The numbers of egg rafts laid by Cx. tarsalis on water that previously contained mosquitofish (Gambusia affinis) were 80-90% lower than on water that was not exposed to potential larvivores.  Not surprisingly, mosquito species, such as Aedes aegypti, that lay eggs in small containers did not respond differentially to fish-conditioned water.  Adena Why is following up these studies by investigating the responses of egg-laying mosquitoes to other potential predators of mosquitoes and by identifying the semiochemicals that elicit responses in gravid mosquitoes.

 

A prior research emphasis in my laboratory was the evolution of resistance to bacterial larvicides and the ecological consequences of evolved resistance.  Bacterial larvicides are perhaps the most promising method of environmentally friendly mosquito control currently available, particularly in treatment wetlands.  Two bacteria species are currently used for mosquito control in California; Lysinibacillus sphaericus is comparatively more effective than is Bacillus thuringiensis subsp. israelensis (Bti) against mosquitoes inhabiting the organically enriched waters of most treatment wetlands.  Unlike Bti which contains multiple toxins that limit the potential for the rapid evolution of resistance in mosquitoes, the two toxin precursors in L. sphaericus act as a single toxin following ingestion and partial digestion by mosquito larvae.  Mosquitoes can evolve resistance to the L. sphaericus toxin very rapidly (>10,000-fold in 7-8 generations).  This finding

 
 
takes on added significance for mosquito control in treatment wetlands of southern California because our studies of mosquito dispersal demonstrated that there is little potential gene exchange among populations of the predominant mosquito occurring at thickly vegetated wetlands.  Consequently, there is a greatly reduced potential for a resistant population to exchange genes with a nearby population that is susceptible to L. sphaericus.

 

We were collaborating with Dr. Brian Federici and his laboratory on an NIH-funded project studying the development, modes of action and spectra of resistance/cross-resistance of transgenic strains of Bacillus that have been engineered for both increased efficacy against mosquitoes and a reduced potential for the evolution of resistance in the target mosquito populations.  Dr. Margaret Wirth, who recently retired from UCR, coordinated this work in my laboratory and, in addition to her considerable expertise in studies of insect resistance, oversaw the maintenance of 22 colonies of mosquitoes that were selected for resistance to various Bacillus toxins and insecticides.  We also have collaborated on related projects with colleagues at the Pasteur Institute in Paris, Ohio State University, Cardiff University and Ben-Gurion University of the Negev.  The findings of these studies have important implications for genetic engineering of bacterial larvicides and resistance management in programs using bacterial larvicides as an environmentally-friendly approach to mosquito control and for reducing the incidence of mosquito-borne disease in developing nations.

 

We recently released training videos on testing for resistance in larval mosquitoes.  Links to the overview video and supplementary material, as well as four videos that focus on resistance testing for four commonly used larval mosquito control agents, can be found on the PacVec website.

 

Undergraduate students have participated in many of the research projects in the laboratory. 

 

 

List of publications

 

Recent Teaching:

BIOL 005C, Introductory Evolution and Ecology
BIOL 265, Advances in Population and Evolutionary Biology
ENTM 114, Aquatic Insects

ENTM 127, Insect Ecology

ENTM 203, Entomology Graduate Core Curriculum: Supraorganismal Disciplines
ENTM 255, Seminar in Medical and Veterinary Entomology

ENTM 276, Research Seminar in Medical, Urban and Veterinary Entomology

 

 

 

 

 

Current Staff:

           Aviva Goldmann, Ph.D.

David Popko, M.S.

 

Current Graduate Students:

           Nathan McConnell (Entomology), M.S. candidate

           Julie Tsecouras (Entomology), Ph.D. candidate

           Ben Nyman (Entomology), Ph.D. candidate

          

Current and Recent Undergraduate Students:

         Kimberly Leiva-Alas

         Eric Huynh

         Julia Perez

         Nicole Colindres

         Andrew Garcia

         Cindy Lee

         Emi Colunga

         Vincent Nguyen                                                                 

        

        

          

Prospective Graduate Students:

I am no longer accepting graduate students.

 

Besides serving on committees of graduate students enrolled in the Entomology Graduate Program, I have recently served on the qualifying exam, thesis or dissertation committees of students in the departments of Biology and Environmental Sciences.  I am a Cooperating Faculty Member in the Evolution, Ecology and Organismal Biology Graduate Program. I am associated with the Center for Conservation Biology, the Center for Invasive Species Research and the Center for Infectious Disease Vector Research. Prospective students are welcome to contact me before applying to best determine which program is most appropriate for their interests and prior training.