Wetlands Research

My research interests are broadly defined in the fields of aquatic entomology and aquatic ecology. Research in my laboratory makes contributions to both basic and applied areas of the aquatic sciences, particularly as they relate to the evolving mission of the Agricultural Experiment Station at U.C.-Riverside. In arid southern California, issues related to water are particularly important. Whereas innovative and cost-effective approaches to water/wastewater management and wetland conservation/augmentation are being developed and tested, many of these projects have a drawback: the increased potential for contact of humans and domesticated animals with pestiferous insects and insect vectors of disease-causing pathogens. The awareness of this potential negative aspect of best management practices (BMPs) for processing municipal wastewater, agricultural wastewater and storm water runoff has been brought into the public spotlight with the recent introduction and outbreak of the West Nile virus in California.

One of the areas of focus for my research includes the ecology and control of mosquitoes inhabiting multipurpose constructed wetlands and created wetlands. I have projects studying multipurpose constructed wetlands in San Jacinto, the Prado Basin, and the Coachella Valley in California. The San Jacinto wetland is a prototype for future multipurpose constructed wetlands to be built in arid regions of the United States for post-secondary treatment of wastewater. The Prado wetlands are used to remove pollutants, primarily nutrients, from the Santa Ana River water destined to recharge aquifers used for potable water in Orange County. The Coachella Valley wetlands are used for secondary treatment of municipal wastewater that has undergone only primary treatment. To date, much of the work in my laboratory has focused on the dispersal and bionomics of adult mosquitoes associated with treatment wetlands (Walton and Workman 1998, Walton et al. 1999), quantification of the seasonal and spatial patterns of occurrence of mosquitoes (Walton et al. 1998, Workman and Walton 2000), quantification of larval behavior (Workman and Walton 2003), and assessment of biological control agents for mosquitoes (Offill and Walton 1998, Walton and Mulla 1990, 1991; Walton et al. 1991a, 1991b, 1996, 1997; Walton 2001). I have been partnering with local water districts and vector control agencies to fund much of this work. Alex Van Dam recently completed preliminary studies of the efficacy of the native larvivorous fish, the arroyo chub (Gila orcutti), for mosquito control. The arroyo chub is omnivorous; its diet includes algae, crustaceans and insects including immature mosquitoes. The arroyo chub is a good candidate to replace the mosquitofish (Gambusia affinis) as a biological control agent for mosquitoes in southern California wetlands where non-native mosquitofish are undesirable, are perceived to pose a threat to native fauna, and where riverine conditions have a negative impact on mosquitofish populations. A summary of some our work can be found in the PowerPoint presentation to a meeting of local municipalities and vector control districts.

Left panel: A wetland research cell that has been cleared of emergent vegetation by burning. Center panel: Three vegetation

planting designs. Right panel: Emergent vegetation in a wetland research cell at two years after clearing.

Research in my laboratory also investigates the interaction between design features/management practices for water quality improvement and mosquito production at constructed treatment wetlands (Knight et al. 2003, Walton 2003). For example, we found that design features, such as raised planting beds and deep-water zones, that limit the proliferation of emergent vegetation are more effective at reducing mosquito production than is the repeated harvesting of vegetation from shallow marshes (Thullen et al. 2002, Keiper et al. 2003, Jiannino and Walton 2004). Our studies have shown that current management practices for emergent vegetation to enhance denitrification in wetland marshes significantly enhances mosquito production (Keiper et al. 2003, Sanford et al. 2003, Walton and Jiannino 2005). These practices should be discontinued, especially in regions where treatment wetlands juxtapose human developments. We also have investigated the relationship between the predominant type of nitrogen (reduced forms such as NH₄-N vs. oxidized forms such as NO₃-N) in wastewater and found that mosquito production is strongly linked to loading of reduced forms of nitrogen (Walton et al. 2000, Sanford et al. 2005). Mosquito production in wetlands receiving ammonia-dominated effluent was nearly an order of magnitude greater than from wetlands receiving comparable levels of nitrate-dominated effluent and, unlike the control wetlands where mosquito production declined approximately 2 months after vegetation management, mosquito production was sustained in wetlands receiving ammonium-enriched effluent (Sanford et al. 2005). We also have been investigating the ecological stoichiometry of mosquitoes (Peck and Walton 2005, 2006).

Publications:

· Heft, D. E. and W. E. Walton. 2008. Effects of the El Niño - Southern Oscillation (ENSO) Cycle on Mosquito Populations in Southern California. Journal of Vector Ecology 33(1): In press.

· Van Dam, A. R. and W. E. Walton. 2007. Comparison of Mosquito Control Provided by the Arroyo Chub (Gila orcutti) and the Mosquitofish (Gambusia affinis). Journal of the American Mosquito Control Association 23: 430-441.

· Walton, W. E. 2007. Larvivorous Fish Including Gambusia. In: “Biorational Control of Mosquitoes.” (T. Floore, ed.) American Mosquito Control Association, Bull. No. 7, Mount Laurel, NJ. Journal of the American Mosquito Control Association 23 (2) Suppl.: 184-220.

· Walton, W. E., M. C. Wirth and P. W. Workman. 2007. Environmental Factors Influencing Survival of Threespine Stickleback (Gasterosteus aculeatus) in a Multipurpose Constructed Treatment Wetland in Southern California. Journal of Vector Ecology 32: 90-105.

· Popko, D. A., S.-K. Han, B. Lanoil and W. E. Walton. 2006. Molecular Ecological Analysis of Planktonic Bacterial Communities in Constructed Wetlands Invaded by Culex (Diptera: Culicidae) Mosquitoes. Journal of Medical Entomology 43: 1153-1163. [PDF]

· Peck, G. W. and W. E. Walton. 2006. The Effect of Bacterial Food Quality and Density on Growth and Whole Body Stoichiometry of Culex quinquefasciatus and Culex tarsalis (Diptera: Culicidae). Journal of Medical Entomology 43: 25-33. [PDF]

· Peck, G. W. and W. E. Walton. 2005. The Effect of Natural Assemblages of Larval Foods on Culex quinquefasciatus and Culex tarsalis (Diptera: Culicidae) Growth and Whole Body Stoichiometry. Environmental Entomology 34: 767-774. [PDF]

· Sanford, M. R., K. Chan, and W. E. Walton. 2005. Effects of Inorganic Nitrogen Enrichment on Mosquitoes (Diptera: Culicidae) and the Associated Aquatic Community in a Constructed Treatment Wetland. Journal of Medical Entomology 42:766-776. [PDF] [Corrected version of Table 1]

· Walton, W. E. and J. A. Jiannino. 2005. Vegetation Management to Stimulate Denitrification Increases Mosquito Abundance in Multipurpose Constructed Wetlands. J. Am. Mosq. Control Assoc. 21: 22-27. [PDF]

· Jiannino, J. A. and W. E. Walton. 2004. Evaluation of Vegetation Management Strategies for Controlling Mosquitoes in a Southern California Constructed Wetland. J. Am. Mosq. Control Assoc. 20: 18-26. [PDF]

· Sanford, M. R. and W. E. Walton. 2004. A New Collection Record for Uranotaenia anhydor in Southern California. J. Am. Mosq. Control Assoc. 20: 85-86. [PDF]

· Walton, W. E. 2003. Managing mosquitoes In Surface-Flow Constructed Treatment Wetlands. University of California, Division of Agriculture and Natural Resources. Davis, CA. Publ. No. 8117. 11 pp. Available at: http://anrcatalog.ucdavis.edu/pdf/8117.pdf

· Knight, R. L., W. E. Walton, G. F. O’Meara, W. K. Reisen, and R. Wass. 2003. Strategies for Effective Mosquito Control in Constructed Treatment Wetlands. Ecological Engineering 21: 211-232. [PDF]

· Sanford, M. R., J. B. Keiper, and W. E. Walton. 2003. The Impact of Wetland Vegetation Drying Time on Abundance of Mosquitoes and Other Invertebrates. J. Am. Mosq. Control Assoc. 19: 361-366. [PDF]

· Keiper, J. B., M. Stanczak, and W. E. Walton. 2003. Adult Chloropidae (Diptera) Associated With Constructed Treatment Wetlands Modified by Three Vegetation Management Techniques. Entomological News 114: 205-210.

· Keiper, J. B., J. A. Jiannino, M. R. Sanford, and W. E. Walton. 2003. Effect of Vegetation Management on the Abundance of Mosquitoes at a Constructed Treatment Wetland in Southern California. Proc. Papers Mosq. Vector Control Assoc. Calif. 70: 35-43.

· Workman, P. W. and W. E. Walton. 2003. Larval Behavior of Four Culex (Diptera: Culicidae) from Treatment Wetlands in Southwestern United States. J. Vector Ecology 28: 213-228.

· Keiper, J. B., D. L. Deonier, J. Jiannino, M. Sanford, and W. E. Walton. 2002. Biology, Immature Stages, and Redescriptions of Hydrellia personata Deonier (Diptera: Ephydridae), A Lemna Miner. Proc. Entomol. Soc. Washington 104: 458-467.

· Thullen, J. S., J. J. Sartoris, and W. E. Walton. 2002. Effects of Vegetation Management in Constructed Wetland Treatment Cells on Water Quality and Mosquito Production. Ecological Engineering 18: 441-457.

· Keiper, J. B. and W. E. Walton. 2002. Effects of Three Vegetation Management Strategies on Shore Flies (Diptera: Ephydridae) in Newly Constructed Treatment Wetlands. Ann. Entomol. Soc. Am. 95: 570-576.

· Keiper, J. B., W. E. Walton, and B. A. Foote. 2002. Biology and Ecology of Higher Diptera from Freshwater Wetlands. Annual Review of Entomology 47: 207-232.

· Walton, W. E. 2002. Multipurpose Constructed Treatment Wetlands in the Arid Southwestern United States: Are The Benefits Worth the Risks? In: “Treatment Wetlands for Water Quality Improvement: Quebec 2000 Conference Proceedings (Selected Papers).” (J. Pries, ed.). CH2M Hill Canada Limited, Pandora Press, Waterloo, ON. (Invited paper). pp. 115-123.

· Walton, W. E. 2001. Effects of Triops newberryi (Notostraca: Triopsidae) on Aquatic Insect Communities in Ponds in the Colorado Desert of Southern California. Israel Journal of Zoology 47: 491-512. Invited paper for a Special Issue on the "Ecology of Temporary Pools."

· Keiper, J. B., J. Jiannino, M. Sanford, and W. E. Walton. 2001. Biology and Immature Stages of Typopsilopa nigra (Williston) (Diptera: Ephydridae), A Secondary Consumer of Damaged Stems of Wetland Monocots. Proc. Entomol. Soc. Washington 103: 89-97.

· Workman, P. D. and W. E. Walton. 2000. Emergence Patterns of Culex Mosquitoes (Diptera: Culicidae) at an Experimental Constructed Treatment Wetland in Southern California. J. Am. Mosq. Control Assoc. 16: 124-130. [PDF]

· Keiper, J. B., M. Sanford, J. Jiannino, and W. E. Walton. 2000. Invertebrates Inhabiting Wetland Monocots Damaged by Lepidoptera. Entomological News 111(6): 348-354.

· Keiper, J. B. and W. E. Walton. 2000. Biology and Immature Stages of Brachydeutera sturtevanti (Diptera: Ephydridae), A Hyponeustic Generalist. Annals of the Entomological Society of America 93: 468-475.

· Keiper, J. B. and W. E. Walton. 2000. Biology and Immature Stages of Ochrotrichia quadrispina Denning and Blickle (Trichoptera: Hydroptilidae), A Spring-Inhabiting Scraper. Proc. Ent. Soc. Washington 102(1): 183-187.

· Walton, W. E., J. B. Keiper, J. Jiannino, and M. Sanford. 2000. Effects of Nitrogen Composition and Fish on Mosquito Populations in Constructed Treatment Wetlands. Mosquito Control Research Annual Report. Univ. of Calif., Div. of Agric. & Nat. Resources, Berkeley, CA. pp. 54-56.

· Offill, Y. A. and W. E. Walton. 1999. Comparative Efficacy of the Threespine Stickleback (Gasterosteus aculeatus) and the Mosquitofish (Gambusia affinis) for Mosquito Control. J. Am. Mosq. Control Assoc. 15: 380-390. [PDF]

· Keiper, J. B. and W. E. Walton. 1999. Biology and Morphology of the Mature Larva of Oxyethira arizona Ross (Trichoptera: Hydroptilidae). Pan Pacific Entomologist 75: 212-230.

· Walton, W. E., K. Chan, L. H. Gould, and J. B. Keiper. 1999. Mosquito Production From Three Vegetation Management Practices for Constructed Treatment Wetlands: Preliminary Findings. Proc. Papers Mosq. Vector Control Assoc. Calif. 67: 18-21.

· Walton, W. E., P. D. Workman, and J. B. Keiper. 1999. An Inexpensive Collapsible Pyramidal Emergence Trap for the Assessment of Wetland Insect Populations. Proc. Papers Mosq. Vector Control Assoc. Calif. 67: 15-17. [PDF]

· Keiper, J. B., J. Jiannino, J. Beehler, and W. E. Walton. 1999. Distribution and Abundance of Culicidae and Chironomidae (Diptera) Following Storm Damage in a Southern California Constructed Wetlands. Proc. Papers Mosq. Vector Control Assoc. Calif. 67: 47-54.

· Walton, W. E., P. D. Workman, and C. Tempelis. 1999. Dispersal, Survivorship, and Host Selection of Culex erythrothorax (Diptera: Culicidae) Associated with a Constructed Wetland in Southern California. Journal of Medical Entomology 36: 30-40. [PDF]

· CH2MHILL. 1999. A Mosquito Control Strategy for the Tres Rios Demonstration Constructed Wetlands. Final Report. (W. E. Walton, ed.), City of Phoenix Water Services Department, Phoenix, AZ.

· Walton, W. E. and P. D Workman. 1998. Effect of Marsh Design on the Abundance of Mosquitoes in Experimental Constructed Wetlands in Southern California. J. Am. Mosq. Control Assoc. 14: 95-107. [PDF]

· Walton, W. E., P. D. Workman, L. A. Randall, J. A. Jiannino, and Y. A. Offill. 1998. Effectiveness of Control Measures Against Mosquitoes at a Constructed Wetland in Southern California. J. Vector Ecology 23: 149-160.

· Walton, W. E., M. C. Wirth, P. D. Workman, and L. A. Randall. 1997. Survival of Two Larvivorous Fishes in a Multipurpose Constructed Wetland in Southern California. Proc. Papers Mosq. Vector Control Assoc. Calif. 65: 51-57.

· Walton, W. E., P. D. Workman, and S. Pucko. 1996. Efficacy of Larvivorous Fish Against Culex spp. in Experimental Wetlands. Proc. Papers Mosq. Vector Control Assoc. Calif. 64: 96-101.

· Walton, W. E. and M. S. Mulla. 1991. Integrated Control of Culex tarsalis Larvae Using Bacillus sphaericus and Gambusia affinis: Effects on Mosquitoes and Nontarget Organisms in Field Mesocosms. Bull. Soc. Vector Ecol. 16: 203-221.

· Walton, W. E., M. S. Mulla, M. J. Wargo, and S. L. Durso. 1991. Efficacy of a Microbial Insecticide and Larvivorous Fish Against Culex tarsalis in Duck Club Ponds in Southern California. Proc. Papers Calif. Mosq. Vector Control Assoc. 58: 148-156. [PDF]

· Walton, W. E., N. S. Tietze, and M. S. Mulla. 1991. Consequences of Tadpole Shrimp Predation on Mayflies in Some Californian Ponds. Freshwater Biology 24: 143-154.

· Walton, W. E., E. T. Schreiber, and M. S. Mulla. 1990. Distribution of Culex tarsalis Larvae in a Freshwater Marsh in Orange County, California. J. Amer. Mosq. Contr. Assoc. 6: 539-543. [PDF]

· Walton, W. E., N. S. Tietze, and M. S. Mulla. 1990. Ecology of Culex tarsalis (Diptera: Culicidae): Factors Influencing Larval Abundance in Mesocosms in Southern California. J. Med. Entomol. 27: 57-67.

· Walton, W. E. and M. S. Mulla. 1990. The Influence of Vegetation and Mosquitofish on Culex tarsalis Abundance in Duck Club Ponds in Southern California. Proc. Papers Calif. Mosq. Vector Control Assoc. 57: 114-121. [PDF]