Biology Department

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Cross-Disciplinary Research at Muhlenberg College –
Plant-Insect Interactions

Funded by the National Science Foundation

In nature, the degree to which insects eat plants (herbivory) can be quite variable from location to location. Scientists have traditionally hypothesized that the physical environment can influence a plant, which in turn affects the ability of that plant to defend itself against herbivory. Thus, variation in local conditions is what drives the degree to which certain plants get eaten. More recently, the focus on herbivory has shifted from these environmental influences to biological influences. This has included studies of how predators and parasites of insect herbivores can be signaled chemically by plants being eaten by those insects. In other words, plants are using aromatic or volatile chemicals to attract enemies to their enemies. This type of interaction is referred to as a tritrophic interaction because it involves three feeding or trophic levels: the plant, the herbivore insect, and the predators or parasites of the herbivore. Other biological factors that can influence levels of herbivory include interactions with other plants, and variation in the genetic make-up of the plants

Research on herbivory has typically taken an either-or approach. Many studies have focused on how the physical environment, particularly light, influences plant-insect interactions, but have not considered biological factors such as tritrophic interactions. Conversely, studies of biological factors have been done without considering variation in the physical environment. By not considering both the local environmental conditions and the biological factors simultaneously, the complete picture of how herbivory varies in nature or in agricultural systems has not been fully understood. In this study, a plant ecologist, analytical chemist, insect molecular biologist, and a statistician will take an integrative approach to examine how light interacts with biotic factors in determining levels of herbivory in a natural system. Our study will focus on the caterpillar, Tulip Tree Beauty or Epimecis hortaria, and its primary food source Spicebush or Lindera benzoin. These native insects and plants are abundant in Northeastern forests. The plant, Spicebush, is easily recognizable by its aromatic condition or volatile chemistry.

Feeding rates of this insect on Spicebush have been demonstrated to differ between light and shade environments. Our goal here is explore the mechanisms responsible for this variation. We will examine how differences in light influence leaf characteristics such as leaf digestibility, leaf chemicals that could serve as defense against herbivory, and leaf volatile compounds that may cue the predators or parasites of the insect herbivore. We will also examine how light environment directly and indirectly mediates insect feeding, growth, and development. We will focus on how predation and parasitism of the herbivore, and association with other plants impact our system in relation to light environment. Finally, we will incorporate molecular and plant propagation techniques to test hypotheses about the relative importance of plant genotype and environment in determining levels of herbivory in this system. In so doing, this will be the first study that simultaneously examines how both physical and biological factors, including plant genotype, intersect in the determination of insect feeding rates in a natural, woody plant system.

The interdisciplinary and collaborative aspect of this work and its occurrence at Muhlenberg College, an undergraduate institution dedicated to broad scientific training and community outreach, will provide the opportunity for achieving significant, broader impacts. With the guidance of the investigators and as part of an already vibrant summer research program in the sciences, undergraduate students will develop independent research projects that will support the overall goals of this work. Participating students will have the opportunity to engage fully in science including project conception, experimental design, field and laboratory research, data analysis, presenting in-house and at national meetings, and writing for professional journals. In our work we will integrate a diversity of approaches to studying biological systems. We will model this for students that participate in this research, the other faculty and student researchers in all of sciences and the broader Muhlenberg College community, and local, less privileged high school students and their teachers who we interact with through our existing outreach programming. A Post-Doctoral Research Associate will receive scientific training, and experience and preparation for a teaching/research career at a primarily undergraduate institution. The investigators will also design and teach an interdisciplinary research/seminar course on plant-insect interactions that is based on this collaborative research project. Our model of research will serve to help remove the barriers of specific, discipline-based research, and show that collaboration is vital for fully understanding biological systems.

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This material is based upon work supported by the National Science Foundation under Grant No. 0442049. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.