Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Dr. Vojislava Grbić

Abstract

Two-spotted spider mite (TSSM), or Tetranychus urticae (Koch), is a major agriculture pest known for its rapid development of resistance to pesticides. The analysis of spider mites’ pesticide resistance demonstrated that resistance patterns and frequencies vary between T. urticae strains collected from different geographic locations and host plants. This research aims at characterization of pesticide resistance patterns in mite populations present in greenhouses in the Southwestern Ontario by identifying genetic and metabolic markers of their pesticide resistance. The establishment of these markers lays the basis for development of a pesticide resistance diagnostic tool that will enable prediction of population resistance status based on the resistance-associated markers. The ultimate aim of the project is to enable identification of genetic patterns to be used for recommendations on pesticide use to growers.

In the Fall of 2018, 19 TSSM populations from different Ontario greenhouses and different crops (tomato, eggplant, cucumber, pepper) were collected. First, the bioassay protocols were optimized and then applied to the collected populations to determine their resistance status. Following that, genotyping and RT-QPCR were performed to check for known genetic markers: single nucleotide polymorphisms associated with abamectin, bifenazate, and etoxazole resistance and metabolic markers of detoxification associated with abamectin resistance, respectively. Lastly, the correlation between the genetic/metabolic markers and resistance status was analyzed, and multiple pesticide resistance was assessed. As a result, the pesticide resistance diagnostic tool was developed for abamectin. More informative markers are needed for bifenazate diagnostic tool, and further research is needed for etoxazole. Cross-resistance to abamectin and bifenazate was also observed in three out of 19 greenhouse populations. This work demonstrates that Canadian populations differ greatly from the populations found in other countries. In addition, the high frequency of resistance-associated alleles in tested populations alerts on a need to develop pesticide resistance diagnostic tools to help growers in mite pesticide resistance management.

Summary for Lay Audience

Tetranychus urticae (Koch), or two-spotted spider mite, is one of the most damaging agricultural pests. It is able to feed on over 1,100 plant species, 150 of which are crops. Since TSSM favours hot dry climate, the ongoing global warming contributes to its spread, and it is predicted that TSSM populations will dramatically increase and migrate further north posing eve greater challenge to the sustainability of Canadian agriculture. Rapid pesticide resistance development is another extraordinary ability of TSSM contributing to its status of a pest. Greenhouses are particularly susceptible to spider mites’ infestations because they are isolated, monocultured, with longer growing seasons, and they are subjected to the extensive pesticide use. However, local spider mite populations appear to have different resistance status for different pesticides; thus, it is hard to predict what pesticide would be efficient against the particular spider mite population. Therefore, there is a need for a pesticide resistance predictive tool which would support decision on what pesticide to use. Such a tool will increase the quality of the crop, decrease the cost of the production and help extend the utility of current pesticides.

This research looked at various genetic markers associated with abamectin, bifenazate, and etoxazole resistance, and aimed to find a correlation between the markers and resistance status of 19 spider mite populations collected from various vegetable greenhouses across Ontario in the Fall of 2018. Moreover, the resistance to more than one pesticide was also assessed. In conclusion, the pesticide resistance tool was established for abamectin, further research is needed for bifenazate and etoxazole, and cross-resistance between abamectin and bifenazate was observed.

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