The influence of host plant variation and intraspecific competition on oviposition preference and offspring performance in the host races of Eurosta solidaginis

1. A series of experiments was conducted to measure the impact of plant gen otype, plant growth rate, and intraspecific competition on the oviposition preference and offspring performance of the host races of Eurosta solidagin is (Diptera: Tephritidae), a fly that forms galls on Solidago altissima and Solidago gigantea (Asteraceae). Previous research has shown that both host races prefer to oviposit on their own host plant where survival is much hi gher than on the alternate host plant. In this study, neither host race sho wed any relationship between oviposition preference and offspring performan ce in choosing among plants of their natal host species. 2. The larval survival of both host races differed among plant genotypes wh en each host race oviposited on its natal host species. In one experiment, altissima host race females showed a preference among plant genotypes that was not correlated with offspring performance on those genotypes. In all ot her experiments, neither the altissima nor gigantea host race demonstrated a preference for specific host plant genotypes. 3. Eurosta solidaginis had a preference for ovipositing on rapidly growing ramets in all experiments, however larval survival was not correlated with ramet growth rate at the time of oviposition. 4. Eurosta solidaginis suffered high mortality from intraspecific competiti on in the early larval stage. There was little evidence, however, that fema les avoided ovipositing on ramets that had been attacked previously. This l ed to an aggregated distribution of eggs among ramets and strong intraspeci fic competition. 5. There was no interaction among plant genotype, plant growth rate, or int raspecific competition in determining oviposition preference or offspring p erformance.