Progress 10/01/00 to 09/30/06
Outputs
In 2006 we completed a multi-year project on how mosquito populations are affected by the management of rice straw and winter flooding of rice fields. Rice fields are the main habitat for Culex tarsalis mosquitoes in Northern California in the summer; this mosquito is the primary vector of West Nile Virus in this area. Therefore, it is very important to understand factors that determine its population size. The main findings of this study were that both beneficial predators and mosquitoes increased in response to on-site decomposition of rice straw, and that winter flooding interacts with residual straw to increase mosquito numbers. There was also an association between extremely high mosquito numbers and a mid-season drain and re-flood of the rice fields. This likely occurred because Culex tarsalis mosquitoes prefer to lay eggs in freshly flooded habitat, and because beneficial predators are initially not abundant enough to control mosquitoes. A final publication
presenting these results appeared in the Journal of Medical Entomology (Lawler and Dritz 2006). Other completed research addressed the effects of an agricultural insecticide on riceland mosquitoes and beneficial predators; this will appear shortly in Pest Management Science (Lawler and Dritz, in press). Lambda-cyhalothrin is increasingly used to control a variety of pests in rice. However, our work shows that this material has a large impact on beneficial predators in rice fields, and that mosquito populations recover faster than predators after its use. Lambda-cyhalothrin contributes incidental mosquito control for up to 3 weeks. Its activity fades gradually, which means that it has potential to contribute to the development of insecticide resistance in mosquitoes. We completed a 3rd year of field work for a study of how ultra-low volume applications of synergized pyrethrin for mosquito control affect the invertebrates of wetlands adjacent to rice fields. Although prior years
showed no effect of these applications on non-target invertebrates, we were not confident in the results because there was high variance in invertebrate abundances. We established a mesocosm experiment at Colusa and Sacramento National Wildlife Refuges so that we could control these variables. 15 cattle-watering tanks (12 at Colusa and 3 at Sacramento) were filled with 5 cm of clean dirt and sod, and were flooded with purified water. 6 of the Colusa tanks were fitted with lids on spray nights; these acted as controls; Sacramento was not sprayed. The Colusa Mosquito Abatement District applied pyrethrin with piperonyl butoxide over wetlands on Colusa Refuge 2X per week in Sept. and Oct. of 2006, and left Sacramento Refuge untreated. On the 5th and 10th spray nights, we established 2 cages of 10 Baetidae mayflies and 2 cages of 20-25 Daphnia magna in each mesocosm. We caged adult mosquitoes over the mesocosm arrays to verify the efficacy of the pesticide. Despite effective control of
mosquitoes, survival non-targets was excellent. This indicates low deposition of the insecticide into the wetland.
Impacts
This project has had many important impacts over its five years. For example, results will help mosquito abatement districts prioritize rice fields for inspection and treatment. It is important for them to know that mid-season re-flooding of rice fields can create local mosquito outbreaks. Also, they can save time and effort by not inspecting fields recently treated with lambda-cyhalothrin, but prioritize these fields for re-inspection after 2 weeks in case mosquitoes rebound before predators. Prior work on this project showed that the mosquitofish used as biocontrol in rice fields are vulnerable to lambda cyhalothrin. Work on how rice straw and flooding affect mosquito populations may give insight to long-term trends in mosquito abundances in the Central Valley of California. Our research on ULV pyrethrin has informed discussions between wildlife managers and mosquito abatement agencies as to the safety of mosquito treatments for non-target invertebrates.
Publications
- Lawler, S.P. and D.A. Dritz. 2006. Effects of rice straw and water management on riceland mosquitoes. Journal of Medical Entomology 43:828-832.
- Lawler, S.P. and D.A. Dritz. 2006. (In press). Effects of lambda-cyhalothrin on mosquito larvae and predatory aquatic insects. Pest Management Science. Preview available at: http://www3.interscience.wiley.com/cgi-bin/fulltext/112749929/PDFSTAR T
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Progress 01/01/05 to 12/31/05
Outputs
In 2005 I made significant progress on several projects designed to generate and disseminate knowledge about mosquito production and control in riceland agroecosystems. I completed data analysis and write-up for a three-year project on how rice straw and winter flooding affect mosquito populations in the rice agroecosystem. This study showed that mosquito populations increased in response to on-site decomposition of rice straw, even though beneficial predators also became more abundant. The first paper from this work was the December cover article for Ecological Applications (Lawler and Dritz 2005). A second manuscript has been submitted to the Journal of Medical Entomology; this ms shows that winter flooding interacts with residual straw to increase mosquito numbers, and that draining fields for herbicide applications may lead to unusually dense mosquito populations upon re-flooding. Greg Lanzaro and I completed the U.C. D.A.N.R. extension publication 'Managing
mosquitoes on the farm'. The work is now available online (U.C. DANR, IPM and Mosquito Research Program websites). This publication addresses how to manage mosquitoes in a wide range of agricultural settings, including dairy farms, orchards, rice fields and other row crops, and natural lands adjacent to fields. I revised a second manuscript on how the agricultural pesticide lambda-cyhalothrin affects mosquitoes and beneficial predators, and submitted it to Pest Management Science. Our previous results showing that this pesticide can kill mosquitofish have been incorporated into a California Rice Research Board brochure for growers (see http://www.carrb.com/Facts/Mosquito.HTM). We completed the second year of field work for a three-year study on how ultra-low volume pesticide fogs for mosquito control affect the invertebrates of seasonal wetlands. Seasonal wetlands in rice-growing areas both produce mosquitoes and harbor mosquitoes from adjacent rice fields. The Colusa Mosquito
Abatement District applied a pyrethrin insecticide over wetlands on Colusa Wildlife Refuge twice per week in September and October of 2005, and left Sacramento Wildlife Refuge untreated. We established study areas in three large wetland basins per refuge. We completed two series of light-trapping samples on nights before, during, and after a spray to estimate mortality of flying insects. We collected zooplankton samples and sweep-net samples of aquatic insects from all sites. In addition, we used Daphnia magna as 'sentinel' zooplankton to test whether adulticides affect zooplankton. A parallel study by Cathy Johnson is assessing whether the pesticide precipitated into the wetlands. This work will not be published until after all years of the study are complete.
Impacts
The online paper 'Management of Mosquitoes on the Farm' is a useful reference document for mosquito prevention and control in row crops, dairies and orchards. California's Mosquito and Vector Control Districts and U.C. extension personnel can refer growers to this publication for information. Our work on rice straw management informs growers and mosquito abatement districts about potential mosquito issues associated with on-site decomposition of rice straw and winter flooding.
Publications
- Lawler, S. P. and G. C. Lanzaro. 2005. Managing mosquitoes on the farm. University of California Division of Agriculture and Natural Resources Publication 8158. 19 pp. Online at http://anrcatalog.ucdavis.edu/pdf/8158.pdf
- Lawler, S. P. and D. A. Dritz. 2005. Straw and winter flooding benefit mosquitoes and other insects in a rice agroecosystem. Ecological Applications 15:2052-2059.
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Progress 01/01/04 to 12/31/04
Outputs
We completed our data analysis for last year's study of how the pyrethroid pesticide lambda-cyhalothrin affected mosquitoes and beneficial predators in rice fields, and have submitted a manuscript to the Journal of Medical Entomology presenting our results. The work showed that lambda-cyhalothrin provides incidental mosquito control but has the potential to disrupt biological control and select for resistant mosquitoes. No new work has been funded in on this topic as yet. Together with Dr. Greg Lanzaro, we produced a manuscript that significantly updated and augmented an out-of-print extension publication on mosquitoes in agriculture. The publication 'Mosquitoes on the Farm' had not been updated since the days of widespread DDT use. With the invasion of West Nile Virus into our area, a new publication was overdue. UC IPM has requested minor changes to the ms and it will be re-submitted shortly. This manuscript covers a wide range of agricultural situations, the
mosquito problems they can produce, and ways of remedying or preventing these problems.
Impacts
Publishing our work on lambda-cyhalothrin and mosquitoes will raise awareness of the potential for agricultural insecticides to disrupt mosquito control, and to cause the emergence of strains of mosquitoes that are resistant to pesticides. Few 'families' of pesticides are registered for use against mosquitoes, so it is essential to stay on top of potential problems with resistance. Interest groups include growers, mosquito abatement districts and other public health agencies. Our publication 'Management of Mosquitoes on the Farm' outlines mosquito prevention and control for virtually every kind of grower: dairy operators, row crops, orchards, etc.. Mosquito control matters for livestock production, farmworkers and rural communities. Mosquito outbreaks can affect human health, livestock health and production, and property values. This document will be a useful resource for Mosquito and Vector Control Districts as well as growers; the Mosquito and Vector Control
Association of California encouraged us to produce this document.
Publications
- Lawler, S.P., D.A. Dritz, J.A. Christiansen and A. J. Cornel. (2005) Effects of lambda-cyhalothrin on mosquitoes (Diptera: Culicidae) and predatory insects: assessing biological control disruption and resistance risk. Submitted, Journal of Medical Entomology.
- Lawler, S.P. and G. Lanzaro. (2005) Management of Mosquitoes on the Farm. In revision for University of California Integrated Pest Management Education and Publications.
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Progress 01/01/03 to 12/31/03
Outputs
This year we performed two studies as part of our project 'Mosquito and agricultural pest management in riceland ecosystems'. The first extended our work on how a pyrethroid pesticide, lambda-cyhalothrin (Warrior), affects mosquitoes and beneficial predators (Lawler et al, in press). Warrior is used to control agricultural pests but is not labeled for use against mosquitoes. We tested whether mosquito abatement would benefit from agricultural use of Warrior or whether it would disrupt biological control. This work also included a field assay of survival of pyrethroid resistant mosquitoes, done in collaboration with Anton Cornell. Results show that Warrior controlled non-resistant mosquitoes for several weeks, however control of resistant mosquitoes was much poorer. There was a gradual 'tail-off' in pesticide activity and the pesticide persisted in the sediment. The gradually decreasing mortality caused by the insecticide could favor the emergence of
pyrethroid-resistant strains of mosquitoes. This is of concern for public health because pyrethroids are often used to control adult mosquitoes. Beneficial insect predators recovered faster in this full-scale field study than they did in a prior mesocosm study, indicating that biological control disruption problems might not be as serious as we first feared. The second project assessed how timing of flooding and different rates of fertilizer applications might affect mosquito populations in rice fields. This was a smaller-scale pilot study. Unfortunately, few mosquitoes bred in the one subdivided field allocated to this study, and we doubt we will have conclusive results for mosquitoes. We continue to analyze data on other invertebrates, to test whether beneficial predators responded to flooding or fertilization treatment
Impacts
Our work demonstrates that agricultural use of pyrethroids may help breed resistance to similar pesticides used for mosquito control. We have made presentations to both mosquito control agencies and rice growers, to raise awareness that they should coordinate pesticide rotations if pyrethroid resistance begin to spread.
Publications
- Lawler, S. P., D. A. Dritz and L. D. Godfrey. In press (2004). Effects of the agricultural insecticide lambda-cyhalothrin (Warrior) on mosquitofish (Gambusia affinis). J. American Mosquito Control Assoc.
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Progress 01/01/02 to 12/31/02
Outputs
This project, 'Mosquito and agricultural pest management in riceland ecosystems' is a broadly-based project on ricelands and similarly-managed wetlands. Mosquito management techniques used in rice are also applied to seasonal wetlands managed for duck populations, wetland endemics like tadpole shrimp, and other fauna of concern, therefore this research is conducted in both rice fields and managed wetlands. Assessing the effects of mosquito control on both mosquitoes and wildlife is of increasing importance because the threat of West Nile Virus and other invasive diseases makes it likely that mosquito control will be more widespread in future. Wildlife managers are often suspicious of mosquito control because of the potential for toxins to be introduced into the environment, or for pesticides to harm the food webs that support wildlife. Our data helps managers evaluate risks. Our progress this year includes two publications of research on how ducks, eggs of other
birds, and non-target invertebrates are affected by applications of a mosquito larvicidal oil, Golden Bear 1111 (GB1111). Bird eggs developed normally when GB1111 was applied at label rates, and ducklings maintained their weight and condition when they were corralled in a site treated with this pesticide. However our study raised the concern that application of the oil could lead to feather-matting and loss of thermoregulatory ability for the ducklings in cold weather. Air-breathing aquatic insects were depleted by the pesticide. A third publication shows that a bacteria used to control mosquitoes, B.t.i., is safe for an endangered tadpole shrimp. A new project begun this year evaluated the potential for an agricultural pesticide to disrupt the control of mosquitoes by mosquitofish in rice fields. Label-rate applications of the synthetic pyrethroid insecticide lambda-cyhalothrin caused 100% mortality in mosquitofish, plus loss of all predatory invertebrates. Treated sites became safe
for fish re-introduction after a week, but beneficial invertebrate populations did not recover for at least three weeks. We are preparing a manuscript to present these results.
Impacts
Wildlife managers are using information from our studies of GB1111 Oil and b.t.i. to negotiate pesticide use proposals with mosquito abatement districts (MADs). Mosquito abatement districts also use this information to justify management practices to their boards and regulatory agencies. Our lambda-cyhalothrin work helps MADs maintain biological control by re-introducing fish as needed.
Publications
- Miles, A. K., S. P. Lawler, D. A. Dritz and S. Spring. 2002. Effects of mosquito larvicide on mallard ducklings and prey. Wildlife Society Bulletin 30: 675-682.
- Dritz, D.A., S.P. Lawler, J. Albertson, W. Hamersky and J. R. Rusmisel. 2002. The impact of Bti on the survival of the endangered tadpole shrimp Lepidurus packardi. Proceedings and Papers of the 69th Annual Conference of the Mosquito and Vector Control Association of California. Pp. 88-91.
- Miles, A. K., S. P. Lawler, D. J. Hoffman, P. H. Albers, M. J. Melancon, D. Dritz, S. Spring and D. M. Buscemi. 2001. Experimental assessment of the toxicity of the mosquito larvicide Golden Bear Oil (GB-1111): (1) Field evaluations on ducklings, target and non-target prey survival; (2) Laboratory evaluations on reared mallard and bobwhite eggs, and wild redwing blackbird eggs. Final Report to the U. S. Fish and Wildlife Service Environmental Contaminants Program.
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Progress 01/01/01 to 12/31/01
Outputs
We are in the 3rd year of a project to assess the effects of rice straw management and winter flooding of rice fields on populations of mosquitoes, and other aquatic invertebrates including predators. Rice straw burning is being phased out to improve air quality, and more farmers are now either discing straw into fields and/or flooding fields in winter to decompose straw and attract waterfowl. We now have 3 yrs of invertebrate samples from a set of experimental rice fields in Maxwell, CA, where replicated rice fields were either flooded or unflooded in winter, and where straw was either burned, incorporated into the soil, or rolled down. In both 1999 and 2000, Culex tarsalis larvae were much more abundant in fields where rice straw was not burned, and in 2000 they were also more abundant in winter flooded fields. Winter flooding also benefited most other aquatic invertebrates, including predators of mosquitoes. This year sampling was extended to commercial rice
fields. We sampled 25 fields in Sutter Co. for mosquitoes and invertebrates where field treatments included: burned/winter dry, disced/dry, bale/flood, and disc/flood. Samples from experimental and commercial fields were collected May-September 2001 and are now being processed. Processing and data analysis requires at least 6 months for each year of this project, so further results will be available in 2002.
Impacts
Results to date have informed mosquito abatement districts that new rice straw management techniques are likely to produce larger mosquito populations. Results were also reported to CA Air Resource Board Staff to inform their policy development as they implement the Connelly-Areias-Chandler Rice Straw Burning Reduction Act of 1991.
Publications
- Lawler, S. P., D. A. Dritz, D. Brown, K. Knerl, and D. Lemanager. 2000. Effects of rice straw management on the dynamics of mosquito populations: a food web study. Mosquito Control Research Annual Report 2000: 41-45. University of California and Division of Agriculture and Natural Resources.
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