Advances in resistance monitoring of agricultural pests and in the elucidation of mite reproductive physiology

The work conducted for this dissertation aimed to contribute to 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 examined 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, lead 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 not 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 that 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. 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 is 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 may lead to new ways of mite pest control.