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Early Season Population Dynamics and Residual Insecticide Effects on Bird Cherry-Oat Aphid, Rhopalosiphum Padi in Arkansas Winte

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Early Season Population Dynamics and Residual Insecticide Effects on Bird Cherry-Oat Aphid, Rhopalosiphum Padi in Arkansas Winte University of Arkansas, Fayetteville ScholarWorks@UARK Theses and Dissertations 5-2012 Early Season Population Dynamics and Residual Insecticide Effects on Bird Cherry-oat Aphid, Rhopalosiphum padi in Arkansas Winter Wheat Beven McWilliams University of Arkansas, Fayetteville Follow this and additional works at: http://scholarworks.uark.edu/etd Part of the Entomology Commons, and the Plant Pathology Commons Recommended Citation McWilliams, Beven, "Early Season Population Dynamics and Residual Insecticide Effects on Bird Cherry-oat Aphid, Rhopalosiphum padi in Arkansas Winter Wheat" (2012). Theses and Dissertations. 246. http://scholarworks.uark.edu/etd/246 This Thesis is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of ScholarWorks@UARK. For more information, please contact [email protected], [email protected]. EARLY SEASON POPULATION DYNAMICS AND RESIDUAL INSECTICIDE EFFECTS ON BIRD CHERRY-OAT APHID, RHOPALOSIPHUM PADI IN ARKANSAS WINTER WHEAT EARLY SEASON POPULATION DYNAMICS AND RESIDUAL INSECTICIDE EFFECTS ON BIRD CHERRY-OAT APHID, RHOPALOSIPHUM PADI IN ARKANSAS WINTER WHEAT A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Entomology By Beven McWilliams Rhodes College Bachelor of Science in Biology, 2008 May 2012 University of Arkansas ABSTRACT Bird cherry-oat aphid is a common pest of Arkansas winter wheat. This aphid vectors barley yellow dwarf virus which may cause extensive crop damage and yield loss when wheat is infested by virulent aphids in the fall. Some suggest this damage may be avoided using insecticide seed treatments if growers are unable to delay planting, as is recommended. Field population dynamics of bird cherry-oat aphid during fall 2009 and 2010 was assessed through random sampling of whole plants and pan trapping methods to evaluate aphid immigration. The field plots were divided into four subplots treated with a systemic insecticide seed treatment (thiamethoxam at the recommended rate of 0.148 liters of insecticide per 45 kilograms of seed or 5.0 fluid ounces per 100 lbs of seed) and four untreated plots. Aphids were counted twice weekly in ten 1 m row samples from plant emergence until the end of December. Aphids were classed as small or large nymphs and alates. Winged immigrants were also counted twice weekly in eight pan traps situated at equidistant points within the study fields. Aphid densities in untreated plots increased throughout the season and aphid densities were significantly lower in treated plots. In 2009 winged aphid numbers in untreated fields were significantly greater (mean = 6.54 per meter-row) than in the treated fields (mean = 0.03 per meter-row) (t = 23.48, df = 639, P < 0.0001). Large aphid numbers were greater in the untreated fields (mean = 5.17) than in the treated fields (mean = 0.43) (t = 10.6, df = 639, P<0.0001). Small aphid numbers were greater in the untreated fields (mean = 34.82) than in the treated fields (mean = 0.16) (t = 19.88, df = 639, P<0.0001). In 2010 winged aphid numbers were low but still differed between untreated fields (mean = 0.26 per meter-row) and treated fields (mean = 0.05 per meter-row) (t = 8.75, df = 1197, P<0.0001). Large aphid numbers were greater in the untreated fields (mean = 3.63 per meter- row) than in the treated fields (mean = 0.14 per meter-row) (t = 15.82, df = 1198, P<0.0001). Small aphid numbers were greater in the untreated fields (mean = 34.82) than in the treated fields (mean = 0.16) (t = 19.88, df = 639, P<0.0001). Alate densities in the field were greatest early in the season, declining around two weeks after plant emergence. Winged aphids caught in pan traps roughly related to dates when winged aphids were observed in field samples. Greenhouse studies were conducted using potting soil as well as silt loam and clay (common soil types used for winter wheat in Arkansas). Trials conducted in the greenhouse showed that aphid numbers on treated plants were lower than untreated plants regardless of soil type for up to 20 days. However, insecticidal activity was longer in field-collected soils relative to potting soils, suggesting that future efficacy studies should use natural soils instead of potting soils. Based on field samples and greenhouse experiments, seed treated with thiamethoxam provided excellent control of immigrant aphids for up to 20 days. Thiamethoxam treatment of wheat seed provides some level of aphid suppression beyond the first 20 days after plant emergence, but additional studies are required to more accurately determine the duration of effective control. This thesis is approved for recommendation to the Graduate Council. Thesis Director: ______________________________________________________ Dr. Timothy Kring Thesis Committee: __________________________________________________ Dr. Rick Cartwright __________________________________________________ Dr. Gus Lorenz THESIS DUPLICATION RELEASE I hereby authorize the University of Arkansas Libraries to duplicate this thesis when needed for research and/or scholarship. Agreed _________________________________________________ Beven McWilliams Refused _________________________________________________ Beven McWilliams ACKNOWLEDGEMENTS Special thanks are due to my committee members Dr. Gus Lorenz and Dr. Rick Cartwright, my department head Dr. Robert Wiedenmann, my advisor Dr. Timothy Kring, Dr. Edward Gbur, and lab assistant June Shen for all of their help with my project and the completion of my thesis. Also, special thanks go out to the faculty and staff at the University of Arkansas for their commitment to the University and success of the students. Thanks to the department graduate students including Kelly Carruthers , Ace Lynn-Miller, Bryan Petty, Sam Kim, Jessica Hartshorn, Amber Tripodi, Ray Fisher, Danielle Keeler, my lab mate Carey Minteer, and very special thanks to Kevin Durden. Thank you to all of my other amazing parents, family and friends, I am blessed to have such wonderful people in my life. TABLE OF CONTENTS Page I. INTRODUCTION A. Wheat 1 B. Insect Pests 1 C. Barley Yellow Dwarf Virus 5 D. Barley Yellow Dwarf Virus and Bird Cherry-Oat Aphid Management 6 E. Systemic Insecticides 8 F. Objectives of This Study 10 II. MATERIALS AND METHODS A. Alate Aphid Immigration 11 B. Aphid Population Dynamics 12 C. Insecticide Seed Treatment Residual Activity 13 D. Statistical Analysis 15 III. RESULTS A. Alate Aphid Immigration 2009 16 B. Aphid Population Dynamics 2009 16 D. Alate Aphid Immigration 2010 18 E. Aphid Population Dynamics 2010 18 G. Insecticide Seed Treatment Residual Activity 19 IV. DISCUSSION A. Aphid Population Dynamics 2009 22 B. Aphid Population Dynamics 2010 23 C. Insecticide Seed Treatment Residual Studies 23 D. Future Work 27 V. TABLES 29 VI. FIGURES 37 VII. LITERATURE CITED 38 VIII. APPENDIX 43 LIST OF TABLES Table Page 1. Mean numbers (plus variance) of winged aphids (1a), large aphids (1b) and small aphids (1c) collected from ten, 1 meter-row whole plant samples in the field during 2009. Comparisons were made between numbers of aphids on seed-treated plants and untreated plants. Large aphids included 4 th –instars and alate adults. Small aphids were 2nd and 3 rd instars. Tests were performed using an effect test (SAS Institute, Inc. 2010)._________________________________________________________________ 29 2. Mean numbers (plus variance) of winged aphids (1a), large aphids (1b) and small aphids (1c) collected from ten, 1 meter-row whole plant samples in the field during 2010. Comparisons were made between numbers of aphids on seed-treated plants and untreated plants. Large aphids included 3rd , 4th –instars and alate adults. Small aphids st nd were 1 and 2 instars. Tests were performed using an effect test (SAS Institute, Inc. 2010)._________________________________________________________________ 32 3. Direct counts of aphids on wheat plants grown in different soils, indicating aphid survival 24 hours after the initial aphid application of ten large aphids per plant totaling th 50 aphids per soil-type and treatment by day (including 4 –instars and alate adults). Clay, loam and potting soils for every trial were tested and significance was tested between treated and untreated. Treatments consisted of plants of different ages since germination. Tests were performed using a t-test (SAS Institute Inc., 2010)._________________________________________________________________ 35 4. Slope of population growth of R. padi on wheat plants grown in different soils. Linear slopes were calculated for 7-day periods after aphids were placed on plans. Treatments consisted of plants of different ages since germination. Slopes were compared to determine differences from zero. Tests were performed using a regression analysis (SAS Institute Inc. 2010). Slopes were not calculated for plants aged 4, 8, 10, and 12 days, due to short duration ofsurvival.__________________________________ 36 LIST OF FIGURES Figure Page 1. Yield data collected from field plots at the Arkansas Agricultural Research and Extension Center, Fayetteville, AR during the 2009 and 2010 growing seasons.________________________________________________________________ 37 Introduction Wheat Wheat ( Triticum spp.) is a grass that was originally farmed in the Fertile Crescent region of the Near East. Wheat has been domestically cultivated since around 9,000 B.C. and is one of the most important cereals in the world (Briggle 1980). In 2010,
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