1. The status of pollinating insects is of international concern, but knowledge of the magnitude and extent of declines is limited by a lack of systematic monitoring. Standardised protocols are urgently needed, alongside a better understanding of how different methods and recorders (data collectors) influence estimates of pollinator abundance and diversity. 2. We compared two common methods for sampling wild pollinating insects (solitary bees, bumblebees and hoverflies), pan traps and transects, in surveys of 1km countryside squares (agricultural and semi-natural habitats) and flowering crop fields across Great Britain, including the influence of local floral resources (nectar sugar availability or crop flower density) on the insects sampled. Further, we compared the performance of recorders with differing expertise (non-specialist research staff, taxonomic experts and non-expert volunteers) in applying methods. 3. Pan traps and transects produced compositionally distinct samples of pollinator communities. In the wider countryside, pan traps sampled more species of solitary bee and hoverfly. In flowering crops, transects recorded greater numbers of individual bumblebees, but fewer species. 4. Across all taxonomic groups and countryside and crop samples, transects generally had lower rates of species accumulation per individual collected than pan traps. This demonstrates that differences between methods in estimating richness are not due to sampling effort alone. However, recorders possessing greater taxonomic expertise can produce species accumulation data from transects that is almost commensurate with pan trapping. 5. The abundance and species richness of pollinators (except solitary bees) on transects in the wider countryside was positively related to the availability of estimated nectar sugar. In crops, pollinator abundance responses to flower densities were idiosyncratic according to crop type, but overall the response was positive and negative for transects and pan traps, respectively. 6. Given these taxonomic and context-specific differences in method performance, we assess their suitability for monitoring pollinating insect communities and pollination services. We discuss the relevance of these findings within the context of achieving standardised, large-scale monitoring of pollinating insects.

Crop pollinator pan trap, timed observation and transect dataThis dataset contains abundance data for common groups of insect pollinators collected from 6 sampling locations in 8 conventional fields of apple, strawberry and field beans. Apple orchards were located in Kent (Southern England), field beans fields were located in Berkshire and Oxfordshire (Southern England) and strawberry field were in Yorkshire (Northern England). These data were collected using 3 different methods. Pan traps: 6 yellow, white and blue water trap stations were set up and left for between 8 and 24 hours. Transects: Each transect involved walking 50m of crop over 10 minutes recording all flower visitors observed in a moving window of fixed area alongside the recorder. Stationary observation: All floral visits made by pollinators in a fixed area were recorded for 10 minutes. The number of open flowers in the observation area was also recorded. Each method was carried out simultaneously, over several rounds during crop flowering and only in dry conditions, in temperature 15 oC or greater with no more than light wind.CropPollinator_Pan_Transect_StationaryObservations_2011.xlsx