Date of Graduation

5-2012

Document Type

Thesis

Degree Name

Master of Science in Entomology (MS)

Degree Level

Graduate

Department

Entomology

Advisor

Timothy J. Kring

Committee Member

Rick D. Cartwright

Second Committee Member

Gus M. Lorenz

Keywords

Biological sciences; Barley yellow dwarf; Bird cherry-oat aphid; Rhopalosiphum padi; Systematic insecticide; Thiamethoxam; Winter wheat

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 (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 aphids in untreated fields were significantly higher (mean = 6.54 per meter-row) than in the treated fields (mean = 0.03 per meter-row) (t = 23.48, df = 639, P < .0001). Large aphids were greater in the untreated fields (mean = 5.17) than in the treated fields (mean = 0.43) (t = 10.6, df = 639, P<.0001). Small aphids were greater in the untreated fields (mean = 34.82) than in the treated fields (mean = 0.16) (t = 19.88, df = 639, P<.0001 ). In 2010 winged aphids were low and did not differ between untreated fields (mean = 0.26 per meter-row) and treated fields (mean = 0.05 per meter-row) (t = 8.75, df = 1197, P<.0001). Large aphids 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<.0001). Small aphids were greater in the untreated fields (mean = 34.82) than in the treated fields (mean = 0.16) (t = 19.88, df = 639, P<.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 loam and clay (common soil types used for winter wheat in Arkansas). Trials conducted in the greenhouse showed that aphid numbers on treated plants was lower than untreated plants regardless of soil type for at least up to 48 days. However, the insecticidal activity was longer in both field-collected soils relative to potting soils, suggesting that efficacy studies should used natural soils instead of potting soils. Based on field samples and greenhouse experiments seed treated with insecticide provided excellent control of immigrant aphids for at least the first 48 days.

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