Browsing by Author "James Harper, Committee Member"

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Advances in resistance monitoring of agricultural pests and in the elucidation of mite reproductive physiology
(2010-03-31) Cabrera, Ana Rosa; Christina Grozinger, Committee Member; James Harper, Committee Member; R. Michael Roe, Committee Chair; Clyde Sorenson, Committee Member
The work conducted for this dissertation aimed to contribute in our knowledge regarding resistance monitoring of agricultural pests and mite reproduction. Resistance monitoring of lepidopteran pests exposed to transgenic cotton expressing Bacillus thuringiensis (Bt) toxins is necessary and required to prevent the development of insect resistance. A bioassay was developed using Bt cotton plant extracts to rehydrate a heliothine diet and observe feeding disruption of the cotton pest Heliothis virescens. A diagnostic dose was estimated for two different pyramided Bt cotton varieties. The bioassay was evaluated with field H. virescens populations from North Carolina and two Bt resistant, laboratory strains. Ready to use meal pads containing Bt from cotton plants can be stored for up to 5 months. This bioassay is practical, lower cost and can be adapted for other Bt cotton varieties and Bt crops. This work is described in chapter 1. Mites are important medical and agricultural pests. Currently, there is limited information regarding the regulation of female reproduction in mites and few studies have study mite yolk proteins. A review of the literature was conducted regarding the regulation of female reproduction in mites and a new model for the regulation of vitellogenesis in the Acari was proposed. Relevant work on the regulation of vitellogenesis in insects, crustaceans and ticks, as well as observations on the effects of some insect hormones and their analogs on mite reproduction, leads us to conclude that the prevailing assumption that mites regulate vitellogenesis with high levels of juvenile hormone (JH) may not be correct. As a result of this review a new unifying model for the Acari was developed where ecdysteroids, and no JH, regulate vitellogenesis in mites. This review was published in 2009 in the Journal of Insect Physiology and is presented in chapter 2. In chapter 3, the characterization of the major yolk protein vitellin of the twospotted spider mite, Tetranychus urticae, is presented. This work determined T. urticae vitellin is a glycolipoprotein, although the carbohydrate and lipid content appears to be lower than that of the American dog tick, Dermacentor variabilis. It was clear that spider mite vitellin does not carry heme, a fundamental difference with the tick yolk protein. Finally, T. urticae vitellin migrated as a single band under native-PAGE conditions, but five different bands were observed with isoelectric focusing analysis, indicating that multiple Vgs may be expressed. This conclusion is also supported by the recent evidence that T. urticae ovipositing females express at least 4 vitellogenin (Vg) genes. This work was published in the Journal of Insect Physiology in 2009. Finally, the transcriptome analysis of the predatory mite, Phytoseiulus persimilis, is presented in chapter 4. This is the first transcriptome analysis of a mite and as a result of a 454 pyrosequencing project that yielded 12,556 sequences of transcripts. From those, 11 contigs were similar to arthropod Vgs and 6 to Vg-receptors (VgR). These contigs were further studied with available tools such as the open reading frame finder in Genbank and alignments with ClustalW and stage-specific expression studies were conducted with selected Vg (6) and VgR (3) contigs. Two Vg contigs (11791 and 12365) are likely to correspond to two different Vg genes. Obtaining DNA-sequence information of mite Vg and VgR genes will facilitate the study of the regulation of female reproduction in mites, which can lead to new ways of mite pest control.
Novel Methods of Hematophagous Arthropod Control
(2009-11-24) Bissinger, Brooke Witting; D. Wesley Watson, Committee Member; Christina M. Grozinger, Committee Member; Charles S. Apperson, Committee Member; James Harper, Committee Member; R. Michael Roe, Committee Chair
Ticks are important vectors of human and animal diseases. One protective measure against ticks is the use of personal arthropod repellents. Here, the history and efficacy of tick repellents, discovery of new repellents, and areas in need of attention such as assay methodology, repellent formulation, and the lack of information about the physiology of repellency are reviewed. Studies were conducted to examine the efficacy of the repellent BioUD with the active ingredient 7.75% 2-undecanone, originally derived from wild tomato plants. BioUD was compared with 7 and 15% deet using arm-in-cage studies against the mosquitoes Aedes aegypti and Ae. albopictus. No differences were found in mean repellency over 6 h after application between BioUD versus 7 and 15% deet for Ae albopictus. For Ae. aegypti, no differences were found over the same time period for 7% deet. Compared to 15% deet, BioUD was less repellent over the 6-h test period. Human subject field trials were conducted in North Carolina and Ontario comparing the repellency of BioUD to products containing 25 and 30% deet. BioUD provided the same repellency or was more efficacious than 25 and 30% deet, respectively. Repellent efficacy of BioUD and 98.1% deet against ticks was examined in the laboratory using a choice test between repellent-treated and control filter paper surfaces for Amblyomma americanum, Dermacentor variabilis and Ixodes scapularis. BioUD provided greater repellency against A. americanum and I. scapularis than deet. No difference was found between BioUD and deet against D. variabilis. In head-to-head assays between BioUD and deet, undiluted and 50% dilutions of BioUD were more repellent than undiluted deet against all three species. A 25% dilution of BioUD was more repellent than deet against A. americanum while no differences were found between a 25% dilution of BioUD and deet against D. variabilis and I. scapularis. Based on regression analysis, the concentration of BioUD required for equivalent repellency to 98.1% deet was 39.5% for D. variabilis and 29.7% for I. scapularis. A log-probit model could not be constructed for A. americanum from the dosages tested. Repellency of BioUD was compared to five repellents against A. americanum and D. variabilis in two-choice bioassays on treated versus untreated cotton cheesecloth. Overall mean percentage repellency against both species was greatest for and did not differ significantly between BioUD and products containing 98.1% deet, 19.6% IR3535, and 30% oil of lemon eucalyptus. Products containing 5 and 15% Picaridin and 0.5% permethrin were also repellent compared to untreated controls but to a lesser degree than BioUD. The four most active repellents were directly compared in head-to-head bioassays. BioUD provided significantly greater overall mean percentage repellency than IR3535 for A. americanum and D. variabilis. BioUD was significantly more repellent than oil of lemon eucalyptus for A. americanum but did not differ significantly in repellency against D. variabilis. No statistically significant difference in overall mean percentage repellency was found between BioUD and deet for A. americanum or D. variabilis. Laboratory trials were also conducted to determine the repellent activity of BioUD against D. variabilis on human skin. BioUD repelled ticks at least 2.5 h after application to human skin. Characterization of the expressed genes in the tick central nervous system could lead to a greater understanding of the control of development and reproduction at the molecular level. A transcriptome to the female D. variabilis synganglion identified 21,119 unique putative gene sequences, of which 7,379 had significant matches to the GenBank nonredundant database. Microarray analysis comparing synganglia from unfed, partially fed, and mated replete females revealed that 121 of these genes were differentially regulated.