Project 2: Plant-insect interactions
The interaction between plants and insects is one of the important research
areas in plant ecology and evolutionary biology. Basically, we are interested in
how insects utilize plants as food sources and habitate; how plants resist the
damage by insects; how insects act as a disturbance factor that can influence
the nutrient cycling and dynamics of ecosystem . Among them, the resistant
ability of plants to the attack of insect herbivory has been intensively
studied. However, due to the complex biotic (e.g. plant species, physiological
development stage) and abiotic (e.g. light, temperature, moisture, and soil
nutrients) conditions, the resistance mechanisms of plants vary greatly among
different species and change over time and space. That is, no single factor can
account for all these variations.
I am currently working with Dr. Tom Kolb (School of Forestry, Northern Arizona
University) and Dr. Karen Clancy (Rocky Mountain Research Station, USDA Forest
Service, Flagstaff, Arizona). Our research is focused on the genetic variation
of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco in resistance to western
spruce budworm (Choristoneura occidentalis Freeman ) (Tortricidae). Douglas-fir
is one of the world’s most important and valuable timber trees and is a major
component of the forests in western Northern America. While western spruce
budworm is one of the main defoliators that is primarily associated with the
variety of Douglas-fir in the interior Rocky Mountain areas. The damage caused
by the western spruce budworm ranges from the destruction of a single tree to
entire forest ecosystem. This damage can result in the loss of productivity and
decrease the health of forest ecosystem . Therefore, understanding the
interaction between Douglas-fir and western spruce budworm will be helpful to
the sound management of that system.
We study the genetic variation of Douglas-fir and its resistance mechanisms to
the western spruce budworm on three diferent scales: mature trees in the field
(Arizona and Colorado site), clones and half-sib seedlings in the greenhouse. A
pairs of putatively resistant and susceptible mature trees were identified by
their relative amount of crown damage after several years of heavy defoliation
by western spruce budworm in 1980s. The pair of trees are nearby (less than 30
m) within each site and has the similar micro-climate conditions. The clones are
obtained by grafting the branches that were taken from the upper 1/3 crown of
mature trees in the field to one-year old stocks of Douglas-fir seedings. We
test the following hypotheses simutaneously: photosynthetic compensation, growth
vigor, foliage nutrients, foliage terpenes, and bud burst phenological
asynchrony under the greenhouse experimental conditions. That is, compared to
the susceptible tree phenotypes, the resistant tree phenotypes will have
difference in at least on of the above measurements. Additionally, we
hypothesize that western spruce budworm feeding on resistant tree phenotypes
will have a lower fecundity in terms of fresh pupal weight, number of eggmasses
per female adult, and eggmass viability. This comprehensive study will provide
an understanding of the resistance mechanisms of Douglas-fir to western spruce
budworm herbivory.
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