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United States Department of Agriculture

Agricultural Research Service

Research Project: Effects of Seasonal Bee Emergence Timing on Rates of Parasitism in a Solitary Bee Species

Location: Pollinating Insects-- Biology, Management and Systematics Research

Project Number: 5428-21000-015-16
Project Type: Nonfunded Cooperative Agreement

Start Date: Mar 01, 2014
End Date: Feb 28, 2019

Objective:
The objective of this cooperative research is to understand how shifts in the timing of seasonal bee emergence impacts rates of parasitism in a native bee species. The orchard mason bee (Osmia lignaria) is a solitary bee species that constructs nests inside of hollow reeds and twigs. This bee species is attacked by a diverse range of brood parasites during development, often resulting in high rates of mortality. This study investigates how climate change may disrupt these host-parasite interactions by altering the timing of bee activity.

Approach:
Orchard mason bees are attacked by a number of parasitoid wasps during development, often resulting in high rates of larval mortality. These parasitoids display a wide variety of strategies for gaining entrance to the nest, some of which are highly dependent on host phenology. We predict that host phenological shifts have differential effects on parasitoid species, largely due to parasitoid reproductive strategy. The foothills surrounding Logan, Utah are home to historically large populations of O. lignaria. Managed female bees originating from a Utah population will be randomly assigned to one of five treatments: Treatment A (“early release”), B (“semi-early release”), C (“control”), D (“semi-late release), or E (“late release”) corresponding to a unique numbered tag. Adults will be excised from their overwintering cocoons, and a tag will be attached to the thorax of each female. Marked females will be returned to their respective cocoons and each cocoon will be placed inside of a single nesting tube and returned to wintering conditions. According to treatment, groups of bees will be incubated at warm temperatures to stimulate adult emergence. Each female also will be weighed prior to release in order to determine whether length of cold storage has a measurable impact on bee weight. Emerged bees will be released at nest sites (nesting shelters and tubes) already established in natural areas of northern Utah known to be appropriate O. lignaria habitat. Observations of nesting tubes will begin the day after releasing each group, and will continue for every other day for at least two weeks or until the majority of available tubes are occupied. Each nesting tube will be uniquely marked to have a record of the position and nest construction rate of marked provisioning females as well as for bees from the natural community. Also recorded will be the presence of parasitoids near the nest boxes and the presence of nearby floral resources. In late summer 2014, all nesting tubes will be collected, and x-ray examination of tubes will reveal: (A) the abundance and species identity of nest parasitoids (B) the mortality rate of bee larvae and (C) the host sex ratio. Nest cells will be dissected in order to measure the weight of cocooned adult bees in each treatment group and the weight of parasitoids. These weight measures will serve as a proxy for individual host and parasitoid fitness. To sample the parasitoid community in the region surrounding the study site, sticky traps will be placed in the field every three days over the course of the experiment. In order to avoid reducing the parasitoid population near the experimental nest boxes, these traps will be placed in neighboring locations with historically high O. lignaria populations.

Last Modified: 7/28/2014
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