and four flies, Dilophus nigrostigma (Walker, 1848), Melangyna novaezelandiae (Macquart, 1855), Eristalis tenax (Linnaeus, 1758) and Melanostoma fasciatum (Macquart, 1850). We used four measures to characterize overall pollinator effectiveness. Two of these were related to pollen transfer efficiency as follows: (i) amount of pollen deposited on stigmas per single visit and (ii) stigmatic contact, and two others related to the rate of visitation: (iii) flower visitation rate (number of flower visits by an individual pollinator per minute) and (iv) visitor abundance per number of available open flowers (measured by observed visits to a 10 × 10 m quadrat per 10 min and corrected for the no. open flowers in the quadrat; Rader et al. 2009). To simplify terminology relating to the rate of visitation, we refer to (iii) as ‘flower visits RO4929097 per minute’ and (iv) as ‘visitor abundance per number of open flowers’. As these measures have been used widely in the literature to quantify and rank individual pollinator contributions to overall pollination services (Primack & Silander 1975; Herrera 1987; Vazquez, Morris & Jordano 2005; Ne’eman et al. 2010), we use all four measures in an attempt to understand the spatial and temporal patterns relating to the provision of pollinator services by unmanaged taxa. To investigate spatial variation in pollen transfer efficiency and visitation rate, we observed flower visitors in four commercial B. rapa fields (two in Lincoln (Lincoln site 1: 43°37′53·92″S; 172°29′03·96″E; Lincoln site 2: 43°37′28·52″S; 172°28′12·46″E) and two in Gore (Gore site 1: 46°07′00·13″S; 168°52′58·74″E; Gore site 2: 46°06′28·89″S; 168°53′35·70″E) on the South Island of New Zealand between December 2006 and February 2007. Fields were selected according to their size (2 ha) and location adjacent to pasture (predominately Lolium perenne) without neighbouring flowering crops. Common flowering weeds were present within field margins at low densities. These included white clover Trifolium repens L., shepherds purse Capsella bursa-pastoris L. (Medik.), hedge mustard Sisymbrium officinale L. (Scop.) and Mallow Malva spp. Because of the large number of honeybee hives operating in close proximity to all four study sites (range 3–8), we assume all honeybee visits were from managed hives. All floral visitor observations were made on sunny or partly cloudy days when the temperature was >16 °C and wind speed <5 ms−1. Pollen deposition was estimated by bagging (fine mesh 50 × 50 um) randomly selected virgin inflorescences in bud to exclude pollinators. When flowers opened, we removed the bag and observed until an insect visited the flower and contacted the stigma in a single visit. After identifying each insect, we removed the stigma by carefully severing it from the style using finely pointed forceps. The stigma was placed on a cube of gelatine-fuchsin (c. 3 × 3 × 3 mm) and a coverslip placed on top.