Date of Award:

8-2020

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Ricardo Ramirez

Committee

Ricardo Ramirez

Committee

Diane Alston

Committee

Niel Allen

Committee

Juan Villalba

Committee

Noelle Beckman

Abstract

Spider mites are well-documented pests of many agricultural crops including cereals such as maize. In hot and dry conditions, when crop plants are under water-stress, spider mite populations can rapidly increase within weeks and can cause severe yield losses. One approach to manage pests, such as spider mites, is through the development and selection of plants that can resist pests. Screening of maize lines has provided evidence of spider mite resistance; however, it is unclear how plant water-stress may affect the ability of maize to sustain spider mite resistance. In addition, it is important to understand how plants respond to a combination of water-stress and the stress of herbivory. The frequency and severity of water-stress conditions are predicted to increase due to climate change. Therefore, understanding the effects of water-stress on maize resistance to spider mites is of critical importance. First, I evaluated the effects of water-stressed maize on the population growth of two species of spider mite, the twospotted spider mite (TSM) that feeds on a wide variety of plants and Banks grass mite (BGM) that feeds specifically on grasses, including maize. In addition, I evaluated plant responses to water-stress and herbivory for each mite species. I found that plants exposed to water-stress had increased spider mite populations. Interestingly, plants responded more when there was a combination of water-stress and TSM herbivory. I followed this with two studies, where I evaluated maize resistance to each mite species and tested whether water-stress affected resistance. I found that TSM was sensitive to maize resistance as its populations remained low, however, BGM feeding and reproduction was apparently unaffected by resistant maize. Furthermore, water-stress did not reduce maize resistance to spider mites. Together, my results show that maize resistance could be an important tool for spider mite management, specifically for TSM, and that this approach can be sustained in maize as water-stress conditions continue to be the new normal.

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