Document: AMY-3-46-5

Host switching: The roles of choice, performance, and host phenology.

WHIPPLE, A.V.*, M.P.BREMER and W.G.ABRAHAMSON

Bucknell University, Lewisburg, PA 17837 ¹

Abstract:
Host switching by phytophagous insects is thought to be the first step along a path to host-race formation and subsequent sympatric speciation. Thus, examining the factors that prevent and promote host switching may help us to understand the process of speciation. The goldenrod gall fly, Eurosta solidaginis, has been shown to exist as two host races on the goldenrods Solidago altissima and S. gigantea. We have found occasional galls on a third goldenrod species, S. canadensis, and flies have emerged from these galls. We wanted to know whether ability to induce galls on S. canadensis or aversion to oviposition on S. canadensis limited the use of this host plant in the field by flies from galls on S. gigantea. We conducted choice and no-choice oviposition experiments in the greenhouse to test these possibilities. Oviposition on the two hosts was equivalent in the choice test. In addition, galls were induced on S. canadensis at a higher rate than on the normal host S. gigantea, although we don't expect survival to adulthood on S. canadensis to be higher. Thus, choice and ability to induce galls do not seem to be any barrier to the use of this new host. Preliminary data suggesting higher galling rates of S. canadensis relative to S. gigantea on younger plants than on older plants, and the elimination of other alternatives, lead us to the new hypothesis that the differential timing of plant susceptibility to galling may be preventing the use of an alternate host plant.

Keywords: host switching, host races, Eurosta

This abstract is being presented at: 2:30 PM in session:
Oral Session #15: Parasitoids and Diseases.