Graduation Date

Fall 2018

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Dr. Michael R. Mesler

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Alexandru M.F. Tomescu

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Paul Bourdeau

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Dr. Erik Jules

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories



Little is known about the pollination biology of the Pacific Coast Irises (Iris: series Californicae, hereafter PCI), especially who visits and pollinates their flowers. In general, Iris flowers are considered bee-pollinated, however, flies in the genus Eulonchus (Acroceridae) are known to visit some PCI members. Therefore, I assessed the relative importance of Eulonchus and other insect visitors to the pollination of a rare PCI species native to the Siskiyou Mountains, I. bracteata.

Methods. I quantified pollinator importance for all flower visitors at sites in northern California and southern Oregon as the product of average visit rate and the probability of stigma contact. I also documented the flower-handling behaviors of each visitor and determined the average number of grains delivered to virgin stigmas by the most frequent flower visitor.

Key results. A diverse set of insects visited the flowers of I. bracteata. Their visitation rates, flower-handling behaviors, and probability of contacting stigmas differed substantially. Contrary to expectations, the fly E. tristis was the most important pollinator; it accounted for more than 70% of total visits and consistently contacted stigmas when entering flowers. The species delivered an average of 185 grains per visit (median=96), which exceeds the average number of ovules per flower (100). Some bees (Osmia densa, Bombus vosnesenskii) likewise contacted stigmas and thus are potential pollinators, but they seldom visited flowers at my study sites.

Implications. My findings contribute to our general understanding of the role that flies play in pollination. Specifically, they show that flies in the genus Eulonchus – and not bees – are the main pollinators of a rare Iris in northern California and southern Oregon. Resource managers concerned about the conservation status of the plant should consider the life history requirements of the flies and, especially, the vulnerability of their larval spider hosts to habitat alteration. Several other plants in the same region are known to be visited by Eulonchus and thus, additional studies assessing their importance as pollinators are warranted.

Citation Style

Journal of Ecology


Thesis/Project Location