Field Sampling
Three large-scale crop production strawberry fields in Southern Ontario
were selected. Since crop field size was the presiding selection
criteria, fields had differing crop varieties, surrounding habitat, and
pollinator-friendly additions, or lack thereof. Fields were within 120
km of each other and within a latitudinal gradient of 0.15 degrees. The
narrow latitudinal gradient was chosen to increase the similarity in
flowering time and temperature fluctuations. All fields had a seven-day
spraying rotation; however, pesticides used are largely unknown and
therefore were not considered. Each field was sampled weekly between May
1st and August 31st of 2018 when the crop reached at least 20% bloom.
Bloom percentage was assessed by walking up a row from the field edge
and counting the number of flowers on each side, to a depth of 50
flowers (100 flowers total); this was repeated in the field centre, and
numbers were averaged. Sampling took place from 09:30 to 16:00 and
consisted of five, hour-long periods followed by a 30-minute break. Each
sampling event was divided into a 30-minute active period and a
30-minute observation period with five sampling events in a day.
During active sampling periods non-bee flower-visitors (excluding
Lepidoptera and Drosophila spp.) were collected directly into
sterile vials and set aside for lab work. Lepidoptera were excluded from
these collection samples, because the scales from their wings would
disrupt the quantification of pollen found on individuals.Drosophila spp. were excluded because they were far too numerous
to capture without affecting the capture rate of other specimens.
Samples were placed in a small cooler containing freezer packs at the
end of each sampling to minimize grooming behaviour and regurgitation.
The remaining 30 minutes of each sampling hour were for observational
sampling, where all flower-visiting insects were identified to the
lowest confident taxonomic unit. This approach provided a non-lethal
sampling method to determine the insect community (including bees) and
reduce collector bias. A small number of bees were sporadically
collected, to provide comparative data on pollen sources and their
abundance. Because this sampling was not standardized, the abundance of
these collections cannot be considered representative of true
populations. Only observational data are representative of bee abundance
at each site. The order of active and passive sampling portions of each
hour periods were randomly selected. Sampling periods rotated between
edge habitat (the edge of the crop, to 50 m into the interior) and
interior habitat (at least 60 m into the crop), while randomizing
whether the first period was interior or exterior. Measurements were
collected for wind speed, rainfall, humidity, and temperature using
AcuRite weather station and solar radiation using a TES 1333R Solar
Power Meter, every half-hour. These environmental measurements were
taken every 90 minutes during sampling (five per sampling day) and
averaged for the analysis.