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
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 had projects studying multipurpose
constructed wetlands in San Jacinto, the
My laboratory group
has been studying the efficacy of a 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 (Van Dam and Walton 2007). A summary of some our work can be found in
the PowerPoint presentation to a meeting
of local municipalities and vector control districts. Jennifer Henke recently completed a study
examining the interaction between the abundance of emergent vegetation and
efficacy of mosquito control provided by arroyo chubs (Henke and Walton 2009) and
Adena Why has been following the outcome of the
introduction of arroyo chubs into constructed treatment wetlands (Why et al.
2014).
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, 2012; Walton et al. 2012, 2013). 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). Narrow vegetation zones (3 m wide) produced
significantly fewer mosquitoes than did wide vegetation zones (20 m wide:
Walton et al. 2012, 2013). Not surprisingly, the fewest mosquitoes were
produced from open water. Our studies
have shown that current management practices for emergent vegetation to enhance
denitrification in wetland marshes significantly enhance 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 rates of constructed
wetlands, especially reduced forms of nitrogen (Walton et al. 2000, Sanford et
al. 2005, Peck and Walton 2008).
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 investigated the ecological
stoichiometry (Peck and Walton 2005, 2006) and microbiomes (Duguma
et al. 2013, 2015) of mosquitoes growing under different levels of nutrient
enrichment. More recently we have been
studying alternative species of emergent vegetation to the large California
bulrush (Schoenoplectus californicus)
for use in constructed treatment wetlands (Popko and
Walton 2013, Duguma et al. 2013, Duguma
and Walton 2014), alternative management strategies for emergent vegetation in
constructed wetlands, and the effects of kairomones
released by larvivorous fishes on mosquito egg-laying
behavior (Van Dam and Walton 2008, Walton et al. 2009).
Publications:
· Walton, W. E.,
D. Duguma, M. Tao, D. A. Popko and S. Nygren. 2016. Integrated mosquito management in
experiment constructed wetlands: Efficacy of small-stature macrophytes and fluctuating hydroperiod. Water 8, 421. Special
issue: Constructed Wetlands for Water Treatment: New Developments. H. Brix, C. A. Arias, and P. N. Carvalho (eds.) doi: 10.3390/w8100421
· Duguma, D., M. Hall,
P. Rugman-Jones, R. Stouthamer, J. D. Neufeld and W.
E. Walton. 2015. Microbial communities and nutrient dynamics in experimental microcosms
are altered after application of a high dose of Bti.
Journal of Applied Ecology. doi:10.1111/1365-2664.12422 [link to Wiley]. [Pre-publication version] [Supplemental material]
· Why, A. M., B.
Johnson, S. Nygren, R. Zembal,
J. Thieme and W. E. Walton. 2014. Suitability of the arroyo chub (Gila orcutti) for the biological control of mosquitoes in a
southern California treatment wetland. Proc. Papers Mosq. Vector Control Assoc.
Calif. 82: 80-89. [PDF]
· Walton, W., N.
McConnell, A. Why, S. Merkley, M. Saba, A. Semrow, R. Cummings, K. Nguyen and J. Newton. 2014. Assessment of native fishes for vector
control in Orange County, California. Proc. Papers Mosq. Vector Control Assoc.
Calif. 82: 70-79. [PDF]
· Duguma, D. and W. E.
Walton. 2014. Effects of nutrients on
mosquitoes and an emergent macrophyte, Schoenoplectus maritimus,
for use in treatment wetlands.
Journal of Vector Ecology 39(1): 1-13 [PDF].
· Popko, D. A., and
W. E. Walton. 2013. Small-stature emergent
macrophytes and crepuscular sprinkler disturbance
reduce mosquito abundance in wetland mesocosms.
Journal of Vector Ecology 38(2): 379-389. [PDF]
· Duguma, D., P.
Rugman-Jones, M. G. Kaufman, M. Hall, J. D. Neufeld, R. Stouthamer
and W. E. Walton. 2013. Bacterial communities associated with Culex mosquito larvae and two emergent aquatic
plants of bioremediation importance. PLoS ONE 8(8):
e72522.
· Walton, W. E.,
D. A. Popko, A. R. Van Dam, and A. Merrill. 2013.
Distribution of Culex species in
vegetation bands of a constructed wetland undergoing integrated mosquito
management. Journal of the American Mosquito Control Association 29: 69–73. [PDF]
· Rey, J. R., W.
E. Walton, R. J. Wolfe, C. R. Connelly, S. M. O’Connell, J. A. Berg, G. E. Sakolsky-Hoopes, and A. D. Laderman. 2012. North American wetlands and mosquito
control. International Journal of Environmental Research and Public Health
9(12): 4537-4605. [PDF] [Special
issue on “Environmental Determinants of Infectious Disease Transmission”, J.
Shaman (ed.)] doi:10.3390/ijerph9124537
· Walton, W. E.
2012. Design and management of free water surface constructed wetlands to
minimize mosquito production. Wetlands Ecology and Management 20: 173–195. [Special
Issue on “Wetlands and Human Health” edited by P. Dale and C. R.
Connelly.] doi:
10.1007/s11273-011-9243-1 The final
publication is available at www.springerlink.com. PDF available upon request.
· Walton, W. E.,
D. A. Popko, A. R. Van Dam, A. Merrill, J. Lythgoe, and B. Hess. 2012. Width of planting beds for
emergent vegetation influences mosquito production from a constructed wetland
in California (USA). Ecological Engineering 42: 150-159. [PDF]
· Berg, J. A.,
M. G. Felton, J. L. Gecy, A. D. Laderman,
C. R. Mayhew, J. L. Mengler, W. H. Meredith, N. R. Read, J. R. Rey, C. Roberts, G. E. Sakolsky-Hoopes, W. E. Walton, and R. J. Wolfe. 2010.
Mosquito control and wetlands. Wetland Science and Practice 27(2): 24-34. [PDF]
· Henke, J. A.,
and W. E. Walton. 2009. Effects of vegetation on the efficacy of larval
mosquito (Diptera: Culicidae)
control by a native larvivorous fish. Proc.
Papers Mosq. Vector Control
· Popko, D. A., M. R.
Sanford and W. E. Walton. 2009. The influence of water quality and vegetation
on mosquitofish in mosquito control programs in wastewater wetlands. Proc.
Papers Mosq. Vector Control
· Walton, W. E.,
A. R. Van Dam and D. A. Popko. 2009. Ovipositional
responses of two Culex (Diptera:
Culicidae) species to larvivorous
fish. Journal of Medical Entomology 48: 1338-1343. [PDF]
· Berg, J., M.
Felton, D. Fish, L. Gecy, A. Laderman,
C. Mayhew, J. Mengler, W. H. Meredith, N. Read, J.
Rey, C. Roberts, G. Sakolsky-Hoopes, W. E. Walton, B.
Warner, and R. Wolfe. (alphabetical list) 2009. Current practices in wetland management
for mosquito control. SWS Web Page. Wetland Concerns Committee. 19p. [PDF]
· Walton, W. E.
2009. Effectiveness of pyramidal emergence traps for estimating production of Culex mosquitoes (Diptera:
Culicidae). Journal of the North American Benthological Society 28: 676-682. [PDF]
· Van Dam, A. R.
and W. E. Walton. 2008. The effect of predatory fish exudates on the ovipositional
behaviour of three mosquito species: Culex quinquefasciatus,
Aedes aegypti and Culex tarsalis. Medical and Veterinary Entomology 22:
399-404. [PDF]
· Peck, G. W.
and W. E. Walton. 2008. Effect of mosquitofish
(Gambusia affinis) and sestonic food abundance on the invertebrate community
within a constructed treatment wetland. Freshwater Biology 53: 2220-2233. [PDF]
· Heft, D. E.
and W. E. Walton. 2008. Effects of the El Nińo - Southern Oscillation (ENSO)
cycle on mosquito populations in southern California. Journal of Vector Ecology
33: 17-29. [PDF]
· 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. [PDF]
· Walton, W. E.
2007. Larvivorous fish including Gambusia. In: “Biorational Control of Mosquitoes.” (T. Floore,
ed.) American Mosquito Control Association, Bull. No. 7,
· 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.
[PDF]
· 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.
· 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
· Workman, P. W.
and W. E. Walton. 2003. Larval behavior of four Culex (Diptera:
Culicidae) from treatment wetlands in the southwestern
United States. J. Vector Ecology 28: 213-228. [PDF]
· 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.
· 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. [PDF]
· 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. [PDF]
· 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,
· Walton, W.
E. 2001.
Effects of Triops newberryi (Notostraca: Triopsidae) on
aquatic insect communities in ponds in the Colorado Desert of southern
California.
· 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.
· 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
· 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.
· 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.
· 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
· 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
· 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
· 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,
· 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
· 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
· 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
· 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