Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Musser, Fred R.

Committee Member

Catchot Jr., Angus L.

Committee Member

Allen, Clint

Committee Member

Dodds, Darrin M.

Committee Member

Caprio, Michael A.

Other Advisors or Committee Members

Krishnan, Natraj

Date of Degree

8-14-2015

Document Type

Dissertation - Open Access

Major

Life Sciences

Degree Name

Doctor of Philosophy

College

College of Agriculture and Life Sciences

Department

Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology

Abstract

Lygus lineolaris (Palisot de Beauvois) is a pest of cotton (Gossypium hirsutum L.) in Mississippi, particularly in the Delta region of the state. It is estimated that 3.1old more insecticide applications are needed to control this pest and it costs producers 3.6old more in the Delta region than in the Hills region. These differences have been attributed to increased insecticide resistance in the Delta and the possibility of a biotype of L. lineolaris in the Delta that is better adapted to cotton than the population in the Hills. A series of experiments were undertaken to evaluate these differences. The first experiment compared developmental time, survival, fecundity, hatch rate, and the cox1 region of the genome of L. lineolaris populations, from both regions, reared on several diets. Data did not reveal any differences in the region of origin but showed that diet had a significant impact on all variables measured except hatch rate. Comparisons of the cox1 region revealed that two cox1 clades exist in the Delta while only one clade exists in the Hills. The second experiment compared the polygalacturonase (PG) system of L. lineolaris from each region. No differences in PG gene expression or enzyme activity, based on the region of L. lineolaris collection, were observed. Specific PG genes that could be a possible target for RNAi insecticides or polygalacturonase-inhibiting proteins in genetically modified cotton were not identified. The third experiment compared LC50s, esterase activity, and glutathione s-transferase (GST) activity of L. lineolaris from the two regions. Data revealed that LC50s and mortality were not different in regards to the region of origin; however, activity of GST revealed a strong trend of higher activity in Delta populations while the activity of esterase was significantly higher in Delta populations, indicating increased metabolic resistance in this region. The fourth study used L. lineolaris nymphs to compare the abilities of Delta and Hills populations to damage cotton in field cages. Damage was minimal and few differences between regions were recorded. Overall, our data revealed that metabolic insecticide resistance was the only difference between the two regions.

URI

https://hdl.handle.net/11668/20647

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