Xianchun Li

Education

B.Sc., 1984, Southwestern Agricultural University, China
M. Sc., 1990, Nanjing Agricultural University, China
PhD., 2003, University of Illinois at Urbana-Champaign
Best Fellow, 2004, University of Toronto

Research

As an insect molecular biologist with interests in evolutionary biology and extensive experience in applied entomology, I mainly use the closely-related Helicoverpa spp. (H. zea, H. armigera, and H. assulta), the pink bollworm (Pectinophora gossypiella), and the invasive and devastating sweet potato whitefly (Bemisia tabaci) species complex (especially B and Q biotypes or species) to explore how insect herbivores adapt to the ever-changing environment. My first focal area of current research addresses the question of how insect herbivores interact with their host plants (Plant-Insect Interactions). The second area focuses on how insect herbivores develop resistance to insecticides and/or Bt toxins and resistance management (Resistance Mechanisms and Management). The third focal area addresses the roles of Transposable elements (TEs) in generating genetic / genomic changes that allow insect herbivores to adapt to host plants and evolve resistance to insecticides and/or Bt toxins and the regulation of TEs in the genome of insect herbivores (Transposable Elements). The three areas are interconnected by a common theme: Environmental Adaptation.

In order to survive and reproduce, insect herbivores, like all organisms living in a native or invaded region, must keep improving their genetic/genomic make-up at the evolutionary time scale and adjusting their gene expression at the ecological time scale to cope with the ever-changing environment. For insect herbivores, perhaps the most important environmental factor they must deal with is host plants, which keep evolving new defenses (e.g. new plant toxins called allelochemicals) at the evolutionary time scale and escalating defenses (e.g. producing more allelochemicals) at the ecological time scale. In addition to host plants, there are other organisms to deal with, and these can be competitors, symbionts, or natural enemies of the herbivore. Insecticides and/or Bt (Bacillus thuringiensis) toxin-expressing transgenic crops used to control herbivores are another important changeable factors that insect herbivores must respond to by changing their genetic make-up and/or gene expression to resist. Also, insect herbivores need to adapt to the changeable abiotic factors such as weather and environmental pollutants. Most of these environmental factors act as pure selection agents rather than mutagens. Therefore, the genetic and genomic variations necessary for insect herbivores to adapt to the changing environment should arise primarily from internal spontaneous mutators. Transposable elements (TEs) are a major source of novel adaptive genomic changes on which natural selection can act.

In the area of plant-insect interactions I have two long-term projects. One addresses the question of how insect herbivores utilize plant-derived signals such as plant defense allelochemicals (i.e. plant toxins) to escalate their counter-defense genes [e.g. allelochemical-detoxifying P450s] for overcoming plant defenses. Such allelochemical inducibility is essential for insect herbivores to cope with a tremendous diversity of allelochemicals idiosyncratically distributed among potential host plants. The second project addresses the long-standing puzzle of host range difference—why most insect herbivores are exceptionally specialized in that they are associated with only one or two host plant families, while others (less than 10%) are extremely generalized in that they feed on dozens, or even hundreds, of host plant families. My research in the area of resistance and pest management mainly focus on resistance of B. tabaci to conventional insecticides, and resistance of H. zea, H. armigera, and P. gossypiella to Bt toxins. In the area of transposable elements, there are two projects in my laboratory. The first is focused on roles of TEs in generating genetic/genomic variability in environmental response genes to cope with the ever-changing environment. Another project addresses the question of how intact TEs are regulated in the host genome.