Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Dr. Vojislava Grbic

2nd Supervisor

Dr. Ian Scott

Joint Supervisor

Abstract

The two-spotted spider mite (TSSM), Tetranychus urticae (Koch), is one of the most damaging agricultural pests in the world. It feeds on over 150 crops, causing considerable yield losses in greenhouses and agricultural fields. Currently, using synthetic acaricides is the main method to control TSSM. However, it can develop resistance to acaricides with repeated exposure, and typically resistance can occur within two to four years. To understand the underlying mechanisms of spider mite adaptation to acaricides is an essential part of resistance management strategy. The resistance ratio of the pyridaben-selected strain compared with the pre-selection strain was estimated at greater than 3000-fold. The results of synergism experiments indicated that detoxification by cytochrome P450 enzymes may be the major resistance mechanism to pyridaben by the spider mite population studied. Piperonyl butoxide (PBO), an inhibitor of cytochrome P450 monooxygenases, can be used as an effective synergist to control pyridaben resistant populations of spider mites. RNA interference (RNAi) can be applied as an alternative pest management strategy with less likelihood of developing resistance. Plant-derived Vacuolar-type H+-ATPase RNAi through dsRNA ingestion in spider mites resulted in a significant decrease of the level of V-ATPase transcripts by 36%, while fecundity was reduced by 28%. Unwanted non-target effects often hamper the application of plant-derived RNAi pest management. However, no non-target RNAi effect on mortality and gain weight of cabbage looper and green peach aphid exposed to dsRNAs targeting Vacuolar-type H+-ATPase RNAi through dsRNA ingestion was observed. These results represent a potential delivery method of dsRNA to control spider mites through transgenic plants.