Insect Visitors of Sidalcea hickmanii ssp. petraea (Malvaceae) and Their Effect on Flower, Fruit, and Seed Production

Abstract This study sought to document potential insect pollinators of Neil Rock checkerbloom, Sidalcea hickmanii ssp. petraea (Malvaceae) and measure the effects of pollinator exclusion and plant type on flower, fruit, and seed production. Prior to this study, the pollination requirements of this gynodioecious plant were unknown and potentially complicated by its hermaphroditic and female-only plant types. Analyses showed that pollinator exclusion had no effect on mean number of flowers produced per raceme but significantly reduced the mean number of fruits produced per raceme and mean number of fruits produced per flower, as well as the mean number of seeds produced per raceme in both female-only and hermaphroditic plants. These results suggested that S. hickmanii ssp. petraea is pollinator dependent. Six orders (Hymenoptera, Coleoptera, Homoptera, Lepidoptera, Diptera, and Hemiptera) representing 29 taxa of insects (primarily Hymenoptera – notably Osmia and Hoplitis, and Coleoptera – notably Anthonomus and Trichodes) were collected from flowering S. hickmanii ssp. petraea plants. Adult Anthonomus weevils were observed selectively feeding on the developing fruits of hermaphroditic over female-only plants. This selective predation may have a significant impact on the maintenance of gynodioecy in this endemic, narrowly-isolated subspecies of Sidalcea hickmanii.