PARENT SESSION
Oral Session # 32: Herbivory II: Grasslands.
Presiding: K Suttle
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 200.
Parallel host-race formation among goldenrod herbivores and their parasitoids.
Heard, Stephen*,1, Nason, John2, Stireman, John2, 1 University of New Brunswick, Fredericton, NB, Canada2 Iowa State University, Ames, IA, USA
ABSTRACT- Evidence is mounting that among phytophagous insects, new biodiversity can arise via host-race formation and subsequent speciation - even in sympatry. A few examples of recent host-race formation have been well documented, but it remains unknown whether host-race formation is rampant or is a rare and special process. An ideal system in which to assay the frequency of host-race formation is the community of herbivorous insects and their parasitoids associated with the goldenrods Solidago altissima and S. gigantea. About 100 species of insect herbivore attack these goldenrods, and one of them (the tephritid fly Eurosta solidaginis) has well-known host races (work of Abrahamson et al.). We have used allozyme and mtDNA markers to test for host-associated genetic differentiation in several goldenrod herbivores and their parasitoids. Host-race formation has been common among gallmaking herbivores: genetically distinct host forms attack S. altissima and S. gigantea in E. solidaginis, the gelechiid moth Gnorimoschema gallaesolidaginis, and the cecidomyid fly Rhopalomyia solidaginis, and may also exist in the tortricid moth Epiblema scudderiana. Parasitoids of gallmakers can also show differentiation: distinct forms attacking hosts on S. altissima and S. gigantea appear to exist for an encyrtid parasitoid of Gnorimoschema, Copidosoma gelechiae, and for a torymid parasitoid of Rhopalomyia, Torymus sp. Overall, our results suggest that host-race formation is extremely common, at least for goldenrod gallmakers and their parasitoids; in fact, what is missing to date is much evidence of goldenrod insects that have NOT evolved host races. Cross-lineage surveys such as ours will eventually document phylogenetic and ecological factors that control the likelihood of host-race formation, and therefore shape the origin of new biodiversity, among insects.
Key words: speciation, parasitoid, host-race formation, herbivorous insect