The Roles of Stress and Time in Insect Outbreaks: The Effect of a One Million-Year Successional Gradient and a 100-Year Regional Drought on the Pinyon Needle Scale

Northern Arizona University, Flagstaff AZ

Investigators

Abstract

0075563 Whitham This project examines the underlying role of abiotic stress, as expressed in a one million-year successional gradient of soil development and a 100-year record drought, in explaining local and regional patterns of outbreaks in a keystone insect herbivore. First, the investigators hypothesize that scale herbivory will decrease across a one million-year successional gradient of young to old volcanic soils under the same climatic regime. Second, they hypothesize that new scale outbreaks are created in response to pulse of drought and that scale populations are less stable than high stress sites that suffer chronic attack. The combination of both new outbreaks and chronic infestations of pinyon needle scale provides the basis for a series of experiments that are designed to increase our understanding of the factors that promote and maintain insect outbreaks. These factors will be examined through intensive population studies comparing incipient outbreaks and chronic infestations, as well as reciprocal transplant experiments of soils and plants. These studies represent a critical opportunity to integrate a million-year successional gradient, chronic stress and acute stress events to explain spatial and temporal dynamics of an outbreak species that has expanded during a recent drought to become a regional problem.