Date of Award:

5-2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Edward W. Evans

Committee

Edward W. Evans

Committee

James P. Pitts

Committee

Thomas C. Edwards Jr.

Committee

Eugene W. Schupp

Committee

Lawrence E. Hipps

Abstract

Sagebrush steppe habitat is rapidly declining in the Intermountain West in both quality and quantity. Observed reductions in animal and bird populations associated with sagebrush, invasion of exotic annual grasses such as cheatgrass (Bromus tectorum), and other concerns with climate change have led to a growing awareness of the need to monitor and better understand the rate of habitat loss. Sagebrush lands are subject to periodic loss caused by insect feeding damage, and human activities have the potential to promote unnaturally high levels of such loss. The sagebrush defoliating Aroga moth, Aroga websteri Clarke (Lepidoptera: Gelechiidae), can kill large stands of sagebrush over a short period of time. Despite the cyclic nature of A. websteri outbreaks throughout the Great Basin, there is limited information on the moth’s population dynamics. The goal of this dissertation was to develop effective means of assessing and describing how the Aroga moth abundance changes across the landscape over time, and potentially promoting biological control of the moth (by natural enemies) to prevent unnaturally large, prolonged and destructive outbreaks. Field studies were conducted to: 1) monitor and quantify activity of the Aroga moth and its damage to sagebrush across a montane landscape, 2) assess the effects of parasitoid and floral diversity on parasitism of the moth, and 3) develop a degree-day (°D) model to describe the insect’s development over time as well as field populations studied previously. North-facing stands of sagebrush, characterized by low values of solar radiation, appear to be especially favorable local habitats for the Aroga moth. High habitat suitability may result from favorable microclimate, both in its direct effects on the Aroga moth and in indirect effects tied to sagebrush plant community productivity and performance. Parasitoid and floral diversity differed strongly and predictably across space and time, with greatest overall parasitism occurring when three major parasitoid species were present. Field experiments revealed individual species of parasitoids differed substantially and complemented one another in their patterns of attack among local populations of the Aroga moth across the montane landscape. Differing responses to provision of floral resources and methyl salicylate (an herbivore-induced plant volatile) support the general hypothesis that over large scales of space and time, species diversity of natural enemies promotes suppression of insect herbivores. Lastly, degree-day models were developed and least variation among years in (°D) phenology resulted with the single-sine method with base temperature of 5°C. Years of historical Aroga moth outbreaks had characteristic seasonal patterns of °D accumulation that were intermediate and characterized by high precipitation in June and July during late stage larval development. Thus it appears that periodic outbreaks of the defoliator are due to favorable weather conditions.

Checksum

40758d488222359b1ef232d484948371

Download

Share

COinS

Copyright for this work is retained by the student. If you have any questions regarding the inclusion of this work in the Digital Commons, please email us at .