DOI: 10.5061/dryad.7m0cfxpsg
title: Data from: Wildflower plantings on fruit farms provide pollen resources and increase nesting by stem nesting bees

description: 1. Wildflower plantings on farms have been shown to attract foraging wild
 bees, however, whether these added floral resources increase nesting
 densities of bees remains largely untested. 2. We placed nest boxes
 containing natural reeds at 20 fruit farms in Michigan. We then compared
 nesting densities between farms with and without wildflower plantings and
 analyzed nest provisions to evaluate use of wildflower plantings for brood
 provisioning. 3. We found significantly greater nesting at farms with
 wildflower plantings, with only one out of 236 completed nests at a farm
 without a planting. The majority of nests were completed by Megachile
 pugnata, with a portion of nests completed by Osmia caerulescens. 4. We
 found that nesting bees collected pollen from only a subset of the
 available flowers in the wildflower plantings, with a strong preference
 for Centaurea maculosa, and Rudbeckia type pollens. While these species
 were found growing in the plantings, only Rudbeckia type species were
 seeded in the plantings. 5. This study provides evidence that wildflower
 plantings (though not only seeded species) are filling a critical resource
 gap for stem-nesting bees in agricultural landscapes and likely support
 local populations.
description: Study locations Twenty commercial fruit
 farms in the western region of Michigan were chosen for this study. These
 were comprised of ten tart cherry (<i>Prunus cerasus</i> L.)
 orchards and ten highbush blueberry (<i>Vaccinium
 corymbosum</i> L.) farms within the main production regions of these
 crops (Fig. 1A). Half of the farms within each focal crop had established
 wildflower plantings (Fig. 1B) which were seeded in 2011 or 2013 (Table
 S1). Locations with plantings were paired with a nearby farm without a
 planting, and paired farms ranged between 1.14 and 12.36 km apart (mean =
 4.55 ± 1.15 S.E.). Most paired farms were managed by the same grower, with
 similar applications of pesticides and weed management strategies (e.g.
 mowing, herbicides, etc.) that could affect the suitability of the
 landscape for bees. All plantings were seeded with a
 mix of native forbs and grasses optimized for wild bee conservation (Table
 S1) and designed to bloom after flowering of the two focal crops. They
 were located in the field margins adjacent to the crop and bordering a
 wooded edge. The plantings ranged in size from 0.08 to 1.97 hectares (mean
 = 0.49 hectares ± 0.17 S.E). Unenhanced, regularly mowed field margins
 that were also adjacent to a wooded edge were selected at the paired
 unenhanced comparison farms (mean = 0.24 hectares ± 0.04 S.E).
 Floral surveys Once every two weeks, floral
 surveys were conducted at each farm. The first visit was in the week of
 June 25, 2018, and surveys continued for 10 weeks (5 total visits per
 farm). At each visit, we walked a 50 m transect in front of the nest box,
 roughly down the middle of the wildflower planting, and parallel to the
 edge of the crop planting and the wood line. Similar transect samples were
 taken at unenhanced comparison farms, again directly in front of the nest
 box. Every 5 m along the transect, a 1m x 1m quadrat was placed on the
 ground. We then visually estimated the proportional cover (between 0 and
 1) of each species of flowering forb within the quadrat. Only the
 flowering head was considered in the estimate, and flowers that were
 obviously pre- or post-bloom were not included. Flowering plants were
 identified to the lowest taxonomic level in the field using Newcomb (1977)
 and the Pl@ntNet app (Joly <i>et al.</i>, 2016), usually to
 species. Any plants that could not be confidently identified in the field
 were brought back to the lab, pressed, and identified using the keys
 available in Newcomb (1977). Nesting
 density At each farm, one 45 cm x 30 cm open faced
 wooden box was mounted three feet off the ground between two metal posts.
 These were placed along the edge of each wildflower planting or unenhanced
 field margin, facing the crop and backing up to a wood line (Fig. 1C).
 Tangle-Trap Sticky Coating (The Scotts Company LLC, Marysville, OH) was
 sprayed on the posts below the boxes to limit ant activity. A wooden bar
 running lengthwise 8 cm below the top of the box was used to hang the
 nesting materials, consisting of 6mm diameter reeds
 (<i>Phragmites</i> sp.) (Crown Bees, Woodinville, WA). Bundles
 of 50 reeds each were assembled using zipties and three of these bundles
 were hung from the crossbar of each nest box. Nest boxes were set up
 during the week of June 11, 2018 and removed the week of September 4,
 2018. At the same time as floral surveys were conducted
 (once every two weeks), all reeds with completed nests were collected and
 replaced with new reeds (Fig. 1D). This included any reeds that had been
 capped at the end (either by Megachilid bees or Eumenid<i>
 </i>mason wasps) or were filled with grass (from grass-carrying
 <i>Isodontia </i>wasps). Though only those reeds completed by
 bees were used for future data analyses. Additionally, ants were
 occasionally found to be stripping parts of the reeds for nesting
 materials, at which time all reeds in the nest boxes were removed and
 replaced, and additional applications of Tangle-Trap were made to the
 posts to reduce ant visitation. All completed nests
 were brought back to the laboratory and the bee nests (N=236) and wasp
 nests (N=37) were separated. If we had collected more than one bee nest
 that day at a farm then one reed per farm, or 10% of collected reeds if
 there were twenty or more collected, were randomly selected for rearing
 out. Nests for rearing (N=24) were then put into mesh pollinator exclusion
 bags which were secured shut with zipties and stored in an unheated barn
 to overwinter. After the first male bees emerged (June 2019), the rest of
 the reeds were frozen and then opened to identify adult bees to species
 using published keys (Arduser, 2009; Sheffield <i>et al.</i>,
 2011). All other collected bee nests were used for pollen identification
 (N=212), and therefore placed in the freezer the same day they were
 collected to halt larval development. Nests used for pollen identification
 were not used to identify bee species. Pollen
 identification from nests Up to 10 nests were randomly
 chosen from each farm on each collection date and opened (Fig. 1E). Pollen
 provisions (bee collected pollen found in each cell) were removed and
 placed in individually labeled tubes. Each pollen provision was then
 suspended in 70% ethanol, with the amount of ethanol added varying in
 proportion to the size of the provision, but typically between 0.5 and 1
 ml. The sample was then vortexed until the pollen was homogenized (2-3
 minutes), and 20μl of the
 sample was immediately placed in the middle of a microscope slide, and the
 ethanol was allowed to evaporate. Pollen grains (Fig. 1F) were then
 stained with fuchsin gel and the sample was covered with a cover slip.
 Volumes of pollen species (Folk, 1951) were visually estimated for each
 sample. We identified the pollen to the lowest taxonomic rank
 possible using Sawyer (1981) and a reference collection of 254 known
 pollen species/types collected by bees in Michigan. Reference slides are
 housed in the Isaacs Lab at Michigan State University, Department of
 Entomology and primarily from west Michigan where our project farms were
 located. Some reference images are also available online:
 http://bit.ly/MSUbeepollen. If the identity of a pollen was uncertain, then it was lumped into a type category. Each pollen type is made up of a group of possible plant species that the pollen could be attributable to (Table 2).