BIODIVERSITY RESEARCH Pollen transport differs among bees and flies in a human-modified landscape Romina Rader 1,2 *, Will Edwards 1 , David A. Westcott 1,3 , Saul A. Cunningham 4 and Bradley G. Howlett 2 INTRODUCTION The potential for landscape-wide pollen movement by insects is a central issue in studies of the ecology and management of both natural and agricultural systems (Hayter & Cresswell, 2006; Hoyle et al., 2007). Pollen transfer is a primary source of gene flow and has direct influence on the level of genetic exchange within and between plant populations (Ellstrand, 1992; Ennos, 1994; Burczyk et al., 2004). Gene flow can be considered either beneficial or detrimental depending on the landscape context in which it occurs. For example, pollen- mediated gene flow between native plant populations is beneficial as it aids gene flow between remnants including isolated trees existing within agricultural or urban land uses, reducing the likelihood of inbreeding depression (Ellstrand, 1992; Richards, 2000; Volis et al., 2005; Ottewell et al., 2009) and ensuring genetic variation exists to facilitate adaptation to future circumstances. Conversely, pollen-mediated gene flow between weeds or crop cultivars in agricultural systems can be undesirable owing to facilitation of weed invasion and/or reduced purity in seed crops (Lavigne et al., 2002; Wilkinson et al., 2003; Fenart et al., 2007), particularly in relation to the potential hybridization of genetically modified crops (Scheffler et al., 1993; Rieger et al., 2002; Devaux et al., 2008). 1 School of Marine and Tropical Biology, James Cook University, PO Box 6811, Cairns 4870, Qld, Australia, 2 The New Zealand Institute for Plant and Food Research Limited, Private Bag 4704, Christchurch, New Zealand, 3 CSIRO Ecosystem Sciences, PO Box 780, Atherton, Qld 4883, Australia, 4 CSIRO Ecosystem Sciences, Box 1700, Canberra, ACT 2601, Australia *Correspondence: Romina Rader, School of Marine and Tropical Biology, James Cook University, PO Box 6811 Cairns 4870, Qld, Australia. E-mail: RominaRader@gmail.com ABSTRACT Aim Dispersal distances of insect pollinators are critical in defining their contribution to landscape-wide pollen movement and ultimately gene flow in natural and agricultural systems. We ask whether bee and fly pollinator taxa differ in their dispersal distances and transport of viable pollen in a human-modified system. Location Canterbury and Otago region, South Island, New Zealand. Methods We captured pollen-carrying insects travelling outside of a model mass- flowering agricultural crop, Brassica rapa, using insect flight intercept traps at five distances (0, 100, 200, 300 and 400 m) from the pollen source. We examined pollen loads and pollen viability to determine whether pollen transport distance and viability differ among pollinator taxa. Results A total of 5453 insects were collected of which 717 individuals from 26 insect taxa were positively identified as dispersing pollen up to 400 m from the source. These taxa consisted of four species from two bee families (Hymenoptera: Apidae and Halictidae), and eight species from four fly families (Diptera: Bibiondae, Stratiomyidae, Syrphidae and Tachinidae). Apidae generally carried higher pollen loads and more viable pollen than most fly taxa. Taxa in the fly families Stratiomyidae and Syrphidae, however, carried pollen to 400 m, which is further than both bee families. Main conclusions A diverse array of wild and managed flower visitors can transport viable pollen from a pollen source to at least 400 m. Knowledge of the differences in transport distances among generalist pollinators in human- modified environments is crucial to understand the potential extent to which (1) pollen transport can facilitate gene flow and (2) unwanted hybridization may occur between crops and related weeds. Keywords Diptera, dispersal, distance, gene flow, hymenoptera, mobility, viability. Diversity and Distributions, (Diversity Distrib.) (2011) 17, 519–529 DOI: 10.1111/j.1472-4642.2011.00757.x ª 2011 Blackwell Publishing Ltd http://wileyonlinelibrary.com/journal/ddi 519 A Journal of Conservation Biogeography Diversity and Distributions