The leaf beetle Ophraella notolata and Ophraella sp. nov. (Coleoptera: Chrysomelidae) that specialize on the asteraceous plants Iva frutescens and Ambrosia artemisiifolia respectively, offer a unique opportunity to examine the relative contribution of the many factors that may act to restrict insect host ranges. Results to date suggest that the species feeding on the derived host plant (O. notulata) retains a greater ability (in terms of behavior and physiology) to utilize the ancestral host than the species (O. sp. nov.) feeding on the derived host. Further, there exists significant genetic variation in both species for the ability to utilize the host of its congener. These results will be expanded and complemented with a series of field experiments in Florida, where the two congeners overlap, to examine the ecological selective pressures that may be operating to restrict host range. The main objectives will be to: 1) test for tradeoffs in larval performance between hosts in the field, 2) examine effects of competition between the two Ophraella species and between each Ophraella species and other phytophages of their host plants, 3) scrutinize the effects of generalist predators and parasitoids, and 4) investigate the behavioral and physiological responses of Ophraella to host plant secondary compounds. It is expected that this effort will yield valuable information about how various intrinsic and extrinsic ecological factors (aspects of plant chemistry, competition, predation, and behavior/physiology) affect host plant utilization. Such knowledge should prove valuable in enhancing our understanding of the processes responsible for shaping patterns of insect host use.
