Copyedited by: OUP Annals of the Entomological Society of America, XX(X), 2018, 1–6 doi: 10.1093/aesa/say028 Research Research Pollen Use by Osmia lignaria (Hymenoptera: Megachilidae) in Highbush Blueberry Fields Mario S. Pinilla-Gallego1,2,4 and Rufus Isaacs1,3 1Department of Entomology, Michigan State University, 578 Wilson Road, East Lansing, MI 48824, 2Applied Ecology Department, North Carolina State University, Campus Box 7617, 100 Brooks Avenue, Raleigh, NC 27607-7150, 3Ecology, Evolutionary Biology, and Behavior Program, Michigan State University, 103 Giltner Hall, 293 Farm Lane, East Lansing, MI 48824, 4Corresponding author, e-mail: [email protected] Subject Editor: Allen Szalanski Received 8 May 2018; Editorial decision 14 July 2018 Abstract The blue orchard bee, Osmia lignaria (Say) (Hymenoptera: Megachilidae), is an alternative managed pollinator of rosaceous tree-crops, and potentially could be used for blueberry (Ericaceae) pollination. However, the floral preferences of this species for other types of flowers could prevent them from visiting blueberry flowers when alternative forage is available. To evaluate O. lignaria suitability for pollination of commercial blueberries in Michigan, we identified the main pollen sources in scopal loads and brood provisions, and determined the contribution of blueberry pollen to pollen collected by females nesting inside or at the border of a large blueberry field. Across two bloom seasons, we found that blueberry pollen was not the most abundant pollen type in either the scopal loads (≈6%) or the brood provisions (13–20%). Black cherry (Prunus serotina, Rosaceae), white clover (Trifolium repens, Fabaceae), and red clover (Trifolium pratese, Fabaceae) were the most abundant pollen types in the brood provisions. While shelter location (inside or at the border of the field) had an influence on the use of some of these plants, it did not affect the use of blueberry pollen. Our results indicate that in these field conditions,O. lignaria visit other plants rather than blueberries as a pollen source, making it poorly suited as an alternative managed pollinator for this specific crop. Key words: blue orchard bee, mason bee, alternative managed bee, palynology, Vaccinium corymbosum Animal pollination is required by many crops to achieve profitable by mud partitions, what give them the name of ‘mason bees’ (Mader yields (Klein et al. 2007), with bees (Hymenoptera: Apoidea) being et al. 2010). Females usually build one cell per day (Phillips and the most important pollinators (Gallai et al. 2009, Garibaldi et al. Klostermeyer 1978), requiring 14 to 35 pollen and nectar foraging 2011, Nogué et al. 2016). European honey bees (Apis mellifera trips to provide one cell, and 12 trips are required to build each mud L.) (Hymenoptera: Apidae) are the most commonly used commercial partition (Torchio 1989). Nests usually have 4–12 cells and a female pollinator; however, in the last few decades beekeepers have faced can build 1–6 nests during the nesting period (Medler 1967, Mader increasing challenges to their management (VanEngelsdorp et al. et al. 2010). 2008, Potts et al. 2010, VanEngelsdorp and Meixner 2010), high- Highbush blueberry (Vaccinium corymbosum) requires insect lighting the importance of finding alternative pollinators for crops pollination for profitable yields (Mackenzie 1997, Ritzinger and (Garibaldi et al. 2013). The blue orchard bee, Osmia lignaria (Say) Lyrene 1999). The flowers produce pollen and nectar, and have pori- (Hymenoptera: Megachilidae), is an alternative managed pollinator, cidal anthers that release pollen by mechanical stimulus (McGregor with a higher pollination efficiency than honey bees for important 1976). For this reason, bees that can buzz-pollinate (e.g., bumble- crops such as apple, cherry, pear, and plum (Torchio 1982, Bosch bees) are more efficient at pollinating blueberries (Javorek et al. and Kemp 1999, Mader et al. 2010, Sheffield 2014). This is due to 2002, Ratti et al. 2008) than those that do not use this behavior, their efficient foraging behavior and strong preference for rosaceous such as honey bees. However, honey bee hives are usually placed in plants (Monzón et al. 2004, Matsumoto et al. 2009). the fields because the high number of visits to the flowers compen- O. lignaria is a univoltine, solitary, cavity-nesting bee (Levin sates for the lack of specialization in behavior (Dedej and Delaplane 1966). They nest in cavities in wood or hollow reeds, building a 2003). series of brood cells that are provisioned with a mix of pollen and Several species of Osmia have been tested for their ability to nectar (Bosch and Kemp 2002, Cane et al. 2007). Cells are separated pollinate blueberry. Osmia ribifloris (Cockerell) (Hymenoptera: © The Author(s) 2018. Published by Oxford University Press on behalf of Entomological Society of America. 1 All rights reserved. For permissions, please e-mail: [email protected]. Downloaded from https://academic.oup.com/aesa/advance-article-abstract/doi/10.1093/aesa/say028/5061887 by D H Hill Library - Acquis S user on 31 July 2018 Copyedited by: OUP Annals of the Entomological Society of America, 2018, Vol. 00, No. 00 Megachilidae) is considered to be specialized on blueberries, and At each location we placed a shelter consisting of pine plywood its nest provisions can be made almost exclusively with blueberry boxes (26 × 28 × 28 cm) with an open face. Each shelter contained pollen (Torchio 1990, Stubbs et al. 1994). Controlled experiments 50 stems (bamboo and natural reeds), approximately 15 cm long (greenhouse or cage) with the same species show that it is effective with an inside diameter of 7–10 mm. Shelters at the border of the at depositing pollen on the stigmas, in some cases achieving the same field were placed facing into the field, while shelters in the field were level of pollination as bumblebees (Bombus spp. Hymenoptera: placed with the open face parallel to the orientation of the plant Apidae) (Sampson and Cane 2000, Sampson et al. 2004). Species rows. Shelters remained in the field between 10 May 2016 and 8 that normally prefer Rosaceous trees (e.g., O. lignaria and Osmia June 2016, and between 6 May 2017 and 13 June 2017, correspond- cornifrons (Radoszkowski) (Hymenoptera: Megachilidae)) have ing to the start and end of blueberry bloom at the site. been found to also be efficient at depositing blueberry pollen on A small emergence box containing O. lignaria loose cocoons was the stigmas (Dogterom 1999, West and McCutcheon 2009), but the placed in each shelter at the start of bloom. In 2016 each emerg- floral preferences that O. lignaria show for rosaceous plants can ing box contained 30 female and 45 male cocoons collected in prevent them from visiting blueberry flowers in the field (Sampson September 2015 from trap nests located at Michigan State University et al. 2009). This is supported by reports that indicate that most of (MSU) campus in East Lansing, MI. In 2017 bees were from trap the pollen found in O. lignaria nests located in agricultural environ- nests located in Fennville, MI, and due to lower availability, each box ments comes from orchard crops (Torchio 1982, Bosch et al. 2006, contained 20 female and 35 male cocoons. Sheffield et al. 2008). Given this background, it is important to explore the pollen use Pollen Samples From Bee Nests by O. lignaria in open field experiments in large areas of blueberry To identify nests built by O. lignaria, we performed a 15-min inspec- production, to determine whether this bee species can be used as an tion of the shelters once per week, recording the location of tubes effective alternative managed pollinator of blueberry, or whether the where O. lignaria was nesting. In 2016, during these sampling peri- promising results described above are relevant only to greenhouse or ods we captured female O. lignaria returning to the nests with pollen caged settings. This is important because of the growing interest in the loads on the scopa. We immobilized them with cold, removed the use of alternative pollinators among growers who are experiencing pollen load with dissecting needles, and stored the pollen in 1.5-ml rising costs for honey bee rentals, and increased variability in spring centrifuge tubes. Bees were released after they recovered from the weather that creates unsuitable conditions for honey bee flight. To cold. On 8 June 2016 and 13 June 2017, when blueberry bloom address this question, the objectives of this study were to 1) determine was complete, tubes occupied by O. lignaria were brought back to the contribution of blueberry pollen to O. lignaria brood provision the laboratory and kept in cold storage (−23°C) until processing. All in a commercial field, 2) determine the plant species used as pollen nests were opened and the whole pollen provision from individual resources by O. lignaria in this setting, and 3) assess whether nest brood cells was collected and stored in individual tubes. The contri- location in the field influences the pollen sources used by O. lignaria. bution of blueberry pollen to mass provisions can be used as a proxy for pollination in blueberry, given than nectar-harvesting visits to flowers only result in pollination in 25% of the cases, in comparison Methods with 85% when bees actively harvest pollen (Javorek et al. 2002). Study System We recorded the total number of nests completed by O. lignaria in This research was carried out during the 2016 and 2017 growing each location and the number of cells per nest. seasons, at a large commercial farm in Pullman, MI (42° 28′ 40.42″ N 86° 1′ 38.50″ W). The farm has an area of approximately 63 ha Plant Richness and Pollen Library dedicated to highbush blueberry (V. corymbosum), with nine varie- To sample blooming-plant richness around each shelter, once per week ties grown, including Jersey, Bluecrop and Nelson, which occupy the we established two transects of 100 × 3 m at each shelter location.