Effects of nest invaders on honey bee (Apis mellifera) pollination efficacy Amanda Ellis 1 , Keith S. Delaplane * Department of Entomology, University of Georgia, 463 Biological Science, UGA, Athens, GA 30602, USA 1. Introduction The role of pollination in terrestrial plant and animal communities is so fundamental that the state of a community’s pollinators constitutes an indicator of its health and sustainability (Kevan, 1999). In the case of agro-ecosystems, pollination is recognized as a natural asset, and if natural pollinators are insufficient then managed pollinators are imported as deliberate inputs (Free, 1993; Delaplane and Mayer, 2000). However, there is evidence that pollinators, both wild and managed, are declining in much of the developed world (National Research Council, 2007). In the case of the western honey bee, Apis mellifera L., this problem is due to a variety of cosmopolitan pests, diseases, and environ- mental toxins taxing managed and feral populations (Cox-Foster et al., 2007). The honey bee is the pollinator of choice in much of its modern range, owing to its manageability and large forager populations (Winston, 1987; Hoopingarner and Waller, 1992; Free, 1993; Delaplane and Mayer, 2000). The annual value of honey bee pollination in the USA has been estimated at over $14 billion (Morse and Calderone, 2000). It is therefore a matter of public interest to sustain high densities of vigorous bee colonies. Varroa mites (Varroa destructor Anderson and Trueman) and small hive beetles (Aethina tumida Murray) are virulent nest invaders of A. mellifera. Varroa decreases a colony’s honey yield (De Jong et al., 1982) and number of pollen foragers (Janmaat et al., 2000). For individual bees, varroa reduces body weight, life span, sperm load in drones, size of mandibular glands, flight activity, and insecticide tolerance (Schmid-Hempel, 1998). Adult small hive beetles reduce colony bee populations, brood area, and flight activity (Ellis et al., 2003). This study examines whether nest invaders limit the efficacy of honey bees as pollinators. A cost to pollination could occur under two scenarios: (1) at the colony level where nest invaders compromise the health of the foraging cohort and reduce their efficacy as pollinators or (2) at the community level where invaders simply kill colonies and reduce the local population of pollinators. It is arguable that a cost to pollination could occur at a level preceding (1), that is, at the level of individual pollinator. However in the case of the honey bee, the pathology of the host and behaviors of its specialist, obligate nest invaders V. destructor and Agriculture, Ecosystems and Environment 127 (2008) 201–206 ARTICLE INFO Article history: Received 4 December 2007 Received in revised form 31 March 2008 Accepted 1 April 2008 Available online 20 May 2008 Keywords: Varroa destructor Aethina tumida Canola Blueberry ABSTRACT The work of pollinators is crucial to the sustainability of plant communities in natural and agricultural ecosystems; however, pollinators are declining in much of the developed world due to a variety of parasites, diseases, and environmental stresses. These experiments are the first to examine directly the impact of honey bee, Apis mellifera, nest invaders on plant pollination and fitness. A cost to pollination could occur under two scenarios: (1) at the colony level where nest invaders compromise the health of the foraging cohort and reduce their efficacy as pollinators or (2) at the community level where invaders simply kill bee colonies and reduce the local pollinator population. Honey bee colonies were manipulated to achieve different levels of the parasitic mite Varroa destructor or nest-invading beetle Aethina tumida and tented under one of two model plants: canola (Brassica napus) or rabbiteye blueberry (Vaccinium ashei). On the basis of single-bee flower visits, fruit-set was reduced in blueberry with bees from varroa- parasitized colonies. However, on the basis of colonies, there were no differences in blueberry fruit-set, number of blueberry pollen tetrads deposited on the stigma, and pod-set in canola among colonies with different levels of nest invaders or no-invader controls. Thus, within the range of nest invader densities used in this study, individual inefficiencies were erased by compensatory multiple flower visits by this colonial pollinator. By failing to affirm the functionality of scenario (1) this study indirectly supports scenario (2): the major contribution of honey bee nest invaders toward a pollinator deficit is the simple eradication of colonies. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +1 706 542 2816. E-mail address: ksd@uga.edu (K.S. Delaplane). 1 Current address: Florida Department of Agriculture & Consumer Services, Bureau of Plant & Apiary Inspection, Gainesville, FL 32615, USA. Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee 0167-8809/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2008.04.001