Graduation Date

Spring 2019

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

Michael Mesler

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Victor Gonzalez

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Erik Jules

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

John Reiss

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories



Premise of the study: Although the study of bees and their pollination services has grown immensely in recent years, the natural history of most solitary bee species is still largely unknown. The goal of this study was to contribute to the natural history dossier of a late-season wool carder bee, Anthidium placitum Cresson (Megachilidae), by establishing which plants it uses as sources of nectar and pollen as well as documenting details of its flower-handling behavior, mating behavior, and nesting biology in northwestern California.

• Methods: Field observations were made at five sites in Del Norte, Humboldt, Siskiyou, and Trinity counties. Pollen use was determined via microscopic examination of samples taken from 244 foraging females and 13 larval provisions. Naturally occurring nests were difficult to find, so I deployed aerial trap nests and created clusters of artificial soil cavities in an effort to obtain nest cells and determine preferred nesting substrate. Light microscopy and SEM were used to identify nest cell trichomes and to check females for specialized clypeal and basitarsal hairs.

• Key findings: Analysis of scopal pollen loads and larval provisions revealed that A. placitum is oligolectic on Cordylanthus tenuis ssp. viscidus (Orobanchaceae). The pollen of this species comprised > 99 % of all samples. Females collect pollen from the nototribic flowers of this species by rubbing specialized clypeal hairs against dorsally located anthers. Both males and females appeared to use flowers of C. tenuis ssp. viscidus as their sole source of nectar. Males displayed resource defense polygyny, aggressively guarding patches of C. tenuis ssp. viscidus as mating venues. Nine nests were discovered, all in pre-existing soil cavities. Natural nests extremely cryptic and distributed in non-aggregated fashion across apparently suitable habitat; 140+ hours of searching yielded only three nests. Six of nearly 1400 artificial holes drilled in the ground yielded nests. Nests contained one or two cells, each constructed entirely of wooly plant hairs. The source of hairs used for cell construction varied across sites, depending on the local availability and relative abundance of wooly-haired plants. Nest entrances were closed with an average of >300 small pebbles and plant parts, which females carried one by one in quick flights from nearby sources. The basitarsi of females covered with dense hairs similar to the tomentum used by other Anthidium to collect extrafloral trichome secretions, but none of the nest cells showed evidence of incorporation of secretions.

• Implications: Effective conservation of native bees depends on understanding critical details of their life histories. Here I show that A. placitum depends on a single plant species for both pollen and nectar. This hemiparasitic forb, in turn, relies on its conifer host trees as a source of water and mineral nutrients. Thus a reduction in the number of these trees via fire, disease, or logging could have a negative impact on the bee. Although attempts to entice bees to use artificial soil cavities as nest sites were largely unsuccessful, with modification this approach may ultimately provide an effective approach for studying the nesting biology of other ground-nesting bees with cryptic, non-aggregated nests.

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