Date of Award

Fall 2013

Degree Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Clifford S. Sadof

Committee Chair

Clifford S. Sadof

Committee Member 1

Ricky E. Foster

Committee Member 2

Ian Kaplan

Committee Member 3

Michael V. Mickelbart

Committee Member 4

Roberto G. Lopez


Potato leafhopper Empoasca fabae (Harris) (Homoptera: Cicadellidae) and maple spider mite Oligonychus aceris (Shimer) (Acarina: Tetranychidae) are important pests of maple trees. Investigations determined how insecticide use and fertilization impacted the abundance of E. fabae and O. aceris on `Red Sunset' red maple and `Autumn Blaze' Freeman maples. Bifenthrin applications directed against leafhoppers reduced damage to both cultivars, but increased O. aceris on Autumn Blaze. Using a threshold of one leafhopper per branch to trigger pesticide applications protected Red Sunset maples from leafhopper injury. It also prevented outbreaks of O. aceris on Autumn Blaze because few trees reached this density. Two phytoseiid mites, Neoseiulus fallacis (Garman) and Typhlodromus caudiglans (Schuster) (Acarina: Phytoseiidae), and one stigmaeid, Zetzellia mali (Ewing) (Acarina: Stigmaeidae) were identified as predators of O. aceris on maple leaves. Populations of Z. mali were higher in both years on Red Sunset than Autumn Blaze. Fertilizer applications on field grown maples increased populations of leafhoppers and spider mites. More damage by E. fabae was observed on fertilized Red Sunset than on fertilized Autumn Blaze trees. O. aceris populations were higher on fertilized Autumn Blaze than fertilized Red Sunset trees. O. aceris populations were positively correlated with nitrogen content in the leaves in both cultivars. Mite populations increased at a lower rate with increasing concentration of nitrogen in the leaves of Red Sunset than on those of Autumn Blaze maples. Differences may be explained by a greater abundance of Z. mali (Ewing) on Red Sunset maples. In laboratory experiments N. fallacis consumed significantly more protonymphs and adults of O. aceris, whereas Z. mali consumed more eggs. N. fallacis consumed more Z. mali on Autumn Blaze than on Red Sunset maple. Z. mali consumed fewer N. fallacis on both maple cultivars than O. aceris. Leaf domatia on Red Sunset leaves provide refugia for Z. mali predators. Absence of leaf domatia on Autumn Blaze left Z. mali no place to hide from N. fallacis and diminished their contribution to O. aceris mortality Thus, differential susceptibility of these cultivars to spider mites is mediated by the capacity of leaf domatia to influence intraguild predation among phtyoseiid and stigmaeid predators.