A Pollination Toolbox for Wild Blueberry Growers

A pollination “toolbox” was developed to facilitate workshops for wild blueberry (Vaccinium angustifolium Aiton) growers. The purpose of the workshop is to provide “hands-on” education about: 1) reproductive biology of wild blueberry; 2) the major pollinators, their life history and identification; 3) conservation and protection of native and commercial bee pollinators; 4) methodology for estimating fruit set, fruit drop, and pollinator field abundance; and 5) the use of a regression model for determining adequacy of pollinator field abundance. The workshop supplies a pollination toolbox to the growers which is comprised of the following materials: 1) a reference bee collection imbedded in plastic; 2) a “field-ready” fruit set estimation kit; 3) a “field-ready” pollinator abundance sampling quadrat; 4) five wild blueberry pollination and pollinator Extension color factsheets; and 5) a video (made in 2013) describing the estimation of fruit set and pollinator field abundance. A survey was given to growers at two workshops in 2014 to assess the workshop and pollination toolbox. This is an on-going project aimed at increasing the knowledge of wild blueberry pollination by growers so that sound decisions can be made in suitable pollination strategies and investments that fit the farm’s management philosophy. INTRODUCTION The wild blueberry (Vaccinium angustifolium Aiton) fields of Downeast Maine represent a unique agroecosystem that differs significantly from other blueberry production systems in the United States (rabbiteye, highbush, and southern highbush). Wild blueberry is native to North America, growing in the understory of native boreal forests and in the sandy acidic soils associated with rocky outcrops, pine barrens and bogs (Hall et al. 1979, Vander Kloet 1988). Fields of blueberry are established by clearing forest, then reducing the presence of plants that compete with wild blueberry (Yarborough 2009). Currently, more than 25,000 hectares of managed stands of wild blueberry are in production (Yarborough 2012). Insect mediated pollination is required for wild blueberry fruit set and subsequent reproduction due to mostly obligate outcrossing among clones (Lee 1958, Aalders and Hall 1961, Aras et al. 1996, Usui et al. 2005, Bell et al. 2010). Bees are the primary pollinators of this plant, although other insect taxa including beetles (Coleoptera), flies (Diptera), ants (Formicidae) and moths (Lepidoptera) have been hypothesized to be additional pollinators (Choate and Drummond 2012, Cutler et al. 2012, Bushmann 2013). There have been more than 100 bee species collected in wild blueberry fields (Bushmann 2013, Jones et al. 2014). The anatomical structure of the poricidal anthers in wild blueberry and other Vaccinium spp. limit a visiting insect's access to the pollen (Bell et al. 2009). Bumble bees (Bombus) and other native bee genera associated with wild blueberry (namely, Andrena, Halictus, Osmia, Megachile, and Lasioglossum) commonly exhibit buzz pollinating (Buchmann 1983) or drumming behaviors to enhance release of pollen (Javorek et al. 2002, Bushmann 2013). Honey bees (Apis mellifera L.) are not known to buzz pollinate wild blueberry (Drummond 2012). Therefore, honey bees are not considered efficient pollinators on an individual bee basis (Javorek et al. 2002, Drummond 2012), although the large numbers of foraging bees per colony make honey bees important pollinators (Aras et al. 1996, Drummond 2002, Drummond 2012, Eaton and Nams 2012, Asare 2013). Historically, wild blueberry growers relied upon the native bee fauna for pollination. However, even as far back as the 1930’s as larger tracks of land were brought into production and insecticides were developed for pest control, native bees were noted to be in decline (Boulanger 1964, Boulanger et al. 1967). As a result of these declines research was initiated to assess the efficacy of honey bees as pollinators of wild blueberry. Between the mid 1950’s to the 1960’s, research with honey bees showed that a migratory honeybee system could provide increases in yield, sometimes doubling the yield (Boulanger 1964). Honey bee importation into Maine has increased from about 500 colonies in 1965, to over 60,000 colonies placed in blueberry fields in 2000 (Drummond 2002), and reached an all-time high of more than 80,000 colonies in 2014 (Yarborough pers. comm.). In the past two decades research on two other commercial bees, the alfalfa leafcutting bee (Megachile rotundata) and the impatient bumble bee (Bombus impatiens) has demonstrated economic utility of these species for pollination of wild blueberry (Stubbs and Drummond 1997a, 1997b, Stubbs et al. 2001, Javorek et al. 2002, Desjardins and De Oliveira 2006, Drummond 2012). Conservation of native bees has also been an area of research in wild blueberry. Strategies for enhancing native bee communities through conserving bee plant forage, as well as providing leafcutting Osmia spp. bees nesting sites and minimizing bee exposure to pesticides have been explored (Stubbs et al. 1992, Drummond and Stubbs 1997a, Drummond and Stubbs 1997b, Stubbs and Drummond 1997, Stubbs et al. 1997b, Stubbs and Drummond 1998, 1999, Stubbs et al. 2000, Drummond 2012a, 2012b, 2012c, 2012d). Educational materials that explain wild blueberry pollination (Drummond 2002), conservation of native bees (Stubbs et al. 2000), bee forage plants (Stubbs et al. 1992), protecting pollinators from pesticide exposure (D'Appollonio-Cote et al. 2013), and the use of honey bees (Drummond 2002), alfalfa leafcutting bees, and bumble bees (Stubbs et al. 1997a, Stubbs et al. 2001) have been published for wild blueberry growers. Wild blueberry growers have adopted many of these varied tactics for improvement of pollination (Hanes et al. 2013, Rose et al. 2013). However, investment in both time and capital for pollination is one of the highest single production costs for wild blueberry growers (Yarborough 2011, Rose et al. 2013). Because of this, in 2013 it was decided to develop a field workshop during bloom that would provide information on wild blueberry pollination biology and hands on training in bee identification, measuring bee foraging force in the field, and estimation of fruit set. This report describes the structure of the workshop and the “toolbox” made for eventual distribution to growers for use in their fields. MATERIALS AND METHODS This project was started in 2013 and continues through 2015. Pollination toolboxes were made for 100 growers, were trialed at field pollination workshops in 2014 and will be distributed to growers in 2015. The chronology of method and materials development for a pollination toolbox is described below. During May and June 2013, a pollination video was designed and shot during the wild blueberry pollination season. This video is an instruction tutorial that aims to demonstrate methods for field estimation of fruit set and bee density (bees / m / min). In addition, use of a regression model to estimate fruit set from bee density was explained and the assessment of set flowers that have a high likelihood of becoming fruit was illustrated. Also during the 2013 bloom period honey bees and native bees were collected on blueberry flowers and stored at 20o C until spring 2014. These collections provided the specimens that comprised a grower reference collection. The raw video was sent to Mr. Michael Wilson and Dr. John Skinner for editing and production during the 2013 fall and 2014 winter. In February through March 2013, most of the components of the pollination toolbox were assembled. Bee sampling frames were made from white PVC plumber’s tubing (0.5 inch OD diam) and elbows. The tubing was cut and fit to make 1.0 yd quadrats. Metal plant tags and twisty wires were purchased and sorted into groups of 30 and bagged in Ziplock bags. One bag is intended for each grower. A bee ID reference collection for growers was constructed from plastic bee molds (clear polyester resin with hardener, Castin’ Craft, poured into plastic square molds). The plastic mold reference collections included a single honeybee, bumble bee, sweat bee (mostly Augochlorella aurata), and sand bee (Andrena spp.). These specimens were selected because they represent the most commonly occurring bee genera and families in Maine wild blueberry fields (Bushmann 2013). Literature was printed for background reading for growers. The following publications were compiled as part of the toolbox: a. Stubbs, C.S. and N. Coverstone. 2001. Understanding native bees, the great pollinators. University of Maine Cooperative Extension, Bulletin #7153. b. Stubbs, C.S., F.A. Drummond, and D. Yarborough. 2001. Commercial bumble bee, Bombus impatiens, management for lowbush blueberry. Wild blueberry fact sheet No. 302 (Bulletin No. 2421). University of Maine Cooperative Extension Publication. 4 pp. c. Drummond, F.A. and C.S. Stubbs. 2003.Wild bee conservation for wild blueberry fields. Univ. Maine Coop. Ext. Fact Sheet 630. 12 pp. d. Drummond, F.A. 2002. Honeybees and Lowbush Blueberry Pollination. http://wildblueberries.maine.edu/FactSheet/NEW629HBPollin.pdf e. D'Appollonio-Cote, J., D. E. Yarborough, and F. Drummond. 2013 Maine Wild blueberry pesticide chart – 1 of 3. http://umaine.edu/blueberries/files/2010/05/2013-ME-Wild-BB-Pesticide-ChartInsecticides.pdf f. Stubbs, C.S., F.A. Drummond, and D. Yarborough. 2000. Field conservation management of native leafcutting and mason Osmia bees. Wild blueberry fact sheet No. 301 (Bulletin No. 2420). University of Maine Cooperative Extension Publication. 6 pp. g. Wild Blueberry Pollinator Poster. Wild Blueberry Producers Association of Nova Scotia. Two grower workshops were scheduled for approximate dates of peak wild blueberry bloom in two Maine growing regions, Coastal and Downeast regions. In the Coastal region a grower’s farm in Warren, Maine was selected for the workshop and in the Downeast region the site selected was the Universi