Date of Award:

5-2017

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Ricardo Ramirez

Committee

Ricardo Ramirez

Committee

Juan Villalba

Committee

Diane Alston

Committee

Niel Allen

Committee

Earl Creech

Abstract

Spider mites (Acari: Tetranychidae) are an important agricultural pest of many crops and landscape plants. They can reproduce rapidly and quickly develop resistance to many pesticides, making them difficult to manage. Plant water-stress and high temperatures promote spider mite infestations, while spider mite outbreaks can also result from neonicotinoid insecticide applications. Drought is predicted to increase in the Intermountain West due to increases in temperature and reduced frequency of precipitation events in the region, and neonicotinoids are currently one of the most widely used classes of insecticides in field crops. I studied the interactive effect of these two simultaneously occurring abiotic factors on spider mite outbreaks and plant biosynthesis of herbivore-related defense proteins. I also evaluated ways to alleviate spider mite outbreaks with drought-tolerant corn and the exogenous application of plant phytohormones involved in plant resistance toward biotic stressors. I found that plant water-stress increased spider mites and that neonicotinoids exacerbated the effect of water-stress. Although applications of plant hormones did not reduce the effect of water-stress and neonicotinoids, drought tolerant corn showed promise in reducing the effect of water-stress and spider mite outbreaks.

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