OVIPOSITION SITE RESOURCE QUANTITY AND LARVAL ESTABLISHMENT FOR ORELLIA-OCCIDENTALIS (DIPTERA, TEPHRITIDAE) ON CIRSIUM-WHEELERI

We investigated factors associated with larval establishment of the te phritid fly Orellia accidentalis (Snow) on die thistle Cirsiun wheeler i (Grey) Petrak. Adult tephritid appearance was temporally synchronize d with the peak flowering of its host plant. During the 14-d period ad ult flies were active, 47% of the capitula were in a phenological stat e appropriate for female oviposition. Plant attributes such as plant h eight or capitulum size were good predictors of potential resource ava ilability. The larval establishment pattern appeared nonrandom. We fou nd a positive correlation between larval establishment and capitulum s ize; the largest capitula are also the rarest in tile population. We p ropose that adult phenology is adaptive, enabling 0. occidentalis acce ss to the largest percentage of resources in the environment for egg l aying and larval development.