UNIVERSITY OF BRITISH COLUMBIA
DEPARTMENT OF FOREST AND CONSERVATION SCIENCES
FRST 498 B.Sc. Thesis in Forestry
Impact of Simulated Mechanical Defoliation caused by Zeiraphera canadensis (Spruce Bud Moth) on Food Resource Availability on Picea glauca (White Spruce) in Subsequent Years
MAY ANNE, THEN
SUPERVISORS DR. ALLAN CARROLL DR. YOUSRY EL KASSABY
APRIL 2015 Abstract
Zeiraphera canadensis (spruce bud moth) larvae feed on newly burst buds of Picea glauca
(white spruce). It has been observed that Z. canadensis herbivory on apical shoots leads to loss of apical dominance and the release of dormant buds in subsequent years due to shoot damage. It has also been observed that there is greater success of larval colonization in years following herbivory. This paper explores whether Z. canadensis herbivory increases the amount of food resource available for subsequent generations by simulating mechanical defoliation in a controlled experiment. The results rejected our original hypothesis and total buds produced was found to decrease with increasing herbivory. We did not observe positive resource regulation feedback in the spruce bud moth and white spruce system.
Key words: Zeiraphera canadensis, Spruce Bud Moth, growth compensation, herbivory, food resource feedback, mechanical defoliation, Picea glauca, White Spruce May Anne Then April 2015
1. Introduction
Native insect folivores are important actors in complex forest ecosystems, with important roles in water and nutrient cycles, as agents affecting successional changes, as plant growth stimulants and other ecosystem processes (Schowalter and Lowman 1999, Trumble et al. 1993).
It is known that folivore populations can not only cause small scale changes (at the tree level) as well as larger effects, such as reducing host plant density and productivity at the landscape level during population eruptions (Schowalter 2006). Host-plant interactions of herbivorous insects can also pose serious implications for forest management, especially when populations reach damaging levels as ‘pests’ due to their significant impacts on tree growth and wood quality
(Schowalter 2006). The spruce bud moth (SBM) and white spruce complex is a well studied system, with many studies since the 1990s focussing on the temporal and spatial patterns of the insect-host relationship and on SBM survivorship.
The spruce bud moth (SBM) larvae, Zeiraphera canadensis Mut. & Free. (Lepidopptera:
Tortricidae) is a native phyllophagous webworm that feeds on foliar buds. Its preferred host is the white spruce, Picea glauca (Moench) Voss, though it also feeds on black spruce trees (Picea marinara). Its native distribution matches that of white spruce and black spruce in Canada and populations have been associated with eruptive spruce budworm levels in the Eastern most provinces (Natural Resources Canada 2011).
An individual insect’s fitness is determined by its response to environmental conditions
(Schowalter 2006). In return, feeding can alter future habitat structure and resource distribution spatially and temporally, either by causing damage to plants after excessive feeding and biomass loss or by inducing growth (Romoser and Stoffolano 1998). Previous studies have shown that the