RUI: Natural-Enemy Response to Herbivore Host-Race Formation: Specialization to Host-Plant Complexes

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ABRAHAMSON 9710109 The incorporation of a novel host into the diet of an herbivorous insect is a common occurrence, and it is thought to be a significant early step in the speciation process. One plausible consequence of herbivore speciation via a host-plant shift is that the herbivore's natural enemies might also undergo speciation in response. The investigators will examine the ecological response of the parasitic wasp, Eurytoma gigantea, to a recent host shift by its herbivorous prey, the goldenrod ball gall inducer (Eurosta solidaginis). Evidence suggests that tall goldenrod (Solidago altissima) was the original host of the gall inducer, and that only more recently was late goldenrod (S. gigantea) incorporated into the gall inducer's diet. The gall inducer currently exists as two distinct "host-associated races" that differ genetically, behaviorally, and physiologically. The objective of this study is to determine if phenotypic differences exist within and among the gall inducer predators. In particular the investigators ask if wasp populations differ in terms of adult oviposition preference for the two host races or if larval performance of the wasp predators differs on the two goldenrod host-races. Insect herbivores and their predators represent a great majority of biological diversity and are of considerable economic significance. Host shifts such as the one described above are common and have been reported for pests of agricultural, forest, endangered, and other native plant species. A shift by an agricultural pest to a new crop species may lead to high economic losses of the new crop species as the herbivore escapes its predators. This study will increase understanding of what may facilitate or limit a corresponding shift by natural enemies onto the novel host plant, and what may influence the evolution of increased efficiency of a predator in the utilization of the new host-plant complex. By directing research toward the adaptation of natural enemies to the plants on w hich their hosts feed, this research may improve the biological control of both native and introduced pests.