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Thesis Format

Integrated Article

Degree

Master of Science

Program

Biology

Supervisor

Vojislava Grbić

Abstract

The phytophagous two-spotted spider mite, Tetranychus urticae (Koch), is a major global pest to agriculture and other plant-production industries. Digestive tract pH is a key factor in regulating the enzymatic activity that facilitates digestion and detoxification of ingested plant cell contents and in my thesis I used various pH indicator dyes to determine the pH of regions of the digestive tract in T. urticae, in vivo. Digital colour values of stained specimen images were cross-referenced with the colour values from images of each dye taken at different pH values to determine the digestive tract pH in non-fed, fed and dsRNA-treated fed mites. The pH of vesicles in early-stage, free-floating midgut cells remained stable regardless of treatments whereas gut lumen pH showed slight changes as a result of feeding and when the expression of the gene tetur09g04140, which codes for V-ATPase subunit a, was downregulated. The identification of pH in the digestive tract of T. urticae can be used to better understand the localization of enzymatic activities responsible for digestive and detoxification processes.

Summary for Lay Audience

Spider mites are versatile pests that can adapt to feed on many different types of plants and quickly develop resistance to toxic chemicals from both plants and pesticides. Thus, they are serious pests in agriculture and other plant-growing industries. The processing of ingested plant material and harmful chemicals is predicted to take place in the mite’s digestive system by a variety of enzymes. Factors such as pH affect the ability of enzymes to perform. In this study I documented the pH in the digestive system of the two-spotted spider mite, Tetranychus urticae, using indicator dyes which show different colours depending on the pH of the substance they are dissolved in. These dyes were fed or injected in normal mites and mites with the gene coding for V-ATPase (a protein complex that regulates pH) was targeted by genetic silencing. The data suggest pH in cells were stable whereas pH in gut compartments showed slight change when the mites were fed and when the production of V-ATPase was interfered with. These results provide information that can be used in future research to find out which enzymes are operating in the mite’s digestive system as well as how active they are.

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