Mediation of Tritrophic Interactions by Oxidative Stress in a Model Plant-Insect-Entomopathogen System

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Baculoviruses are a group of viruses that infect insects. The effect of these viruses on insects, however, appears to vary with the chemical composition of the host plant that the insect consumes. For example, baculoviruses are less able to kill tobacco budworm (Heliothis virescens) when the insect feeds on cotton, than when it feeds on its other host plants such as tomato or lettuce. In this study, the PIs seek to determine the chemical interactions that cause some host plants to render their insect herbivores more resistant to infection by baculoviruses. Preliminary studies have suggested that the generation of reactive oxygen species (ROS) is a major cause of such disease inhibition, but it is unclear how this occurs or what steps in the pathway of infection are being altered by these reactive products. Generation of ROS occurs as a consequence of normal cellular processes but can be altered by ingestion of dietary chemicals. High levels of ROS lead to a condition known as oxidative stress which can damage cellular substances and has been associated with aging and cancer development. ROS can also destroy many microorganisms and appear to interfere with the ability of baculoviruses to kill their host insects. This study will examine whether diet-related ROS interfere with viral infection of insects by damaging the virus or by altering insect immune responses. These investigations should have broad implications for understanding the chemical basis of complex interactions among multiple trophic levels. Additionally, results will contribute to a general understanding of the effects of oxidative stress on disease processes and disease ecology. Finally, because baculoviruses are currently being used as an environmentally-friendly alternative to chemical pesticides, these results may help improve biological control practices in agriculture.