DOI: 10.5061/dryad.jq2bvq8dw
title: Exploring relationships between time of day and pollinator activity in the context of pesticide use - data

description: Pesticide exposure can be harmful to insect pollinators and the ecosystem
 services they provide. As pesticide guidelines warn against applying such
 products when pollinators are active, it is important to determine how
 pollinator activity changes with the time of day and when the most
 appropriate time is to spray these chemicals. We walked transects from
 sunrise to sunset in oilseed rape (Brassica napus L.) fields in Ireland to
 capture the abundance of honeybees, bumblebees, solitary bees, and
 hoverflies across daylight hours. We also recorded the activity of
 representative species from the three bee groups at their nests across
 similar time periods to compare with field observations. Peak pollinator
 abundance was in the mid-afternoon with fewer individuals in the early
 morning and late evening for all groups. At the nest, we observed patterns
 of activity that broadly reflected field abundance but indicated that bees
 are active earlier and later than those observed on the crop. However,
 there were differences between pollinator groups. Overall, honeybee and
 solitary bee abundance and activity were found to peak in the middle of
 the day, while bumblebee abundance and activity were more consistent
 throughout daylight hours. Hoverflies were relatively abundant in the
 morning and increased in number towards the late afternoon and early
 evening. Our results confirm current recommendations that pesticide
 application should be avoided in the middle of the day when pollinators
 are most active. However, the diversity of responses within and between
 pollinator groups to time of day should be accounted for when shaping
 guidelines, and clearly defining optimal pesticide application timings for
 end users is difficult and needs further consideration as it will vary
 between regions and crops. Further research should also explore how time
 impacts pesticide efficacy and exposure of pollinators to residues
 post-application to allow full evaluation of how practical and beneficial
 timing of application may be when aiming to protect pollinators from
 pesticide exposure.
description: <em>Pollinator abundance
 on oilseed rape </em> We observed three fields of mass-flowering
 spring-sown oilseed rape (canola; <em>Brassica napus</em> L.)
 in Co. Carlow, Ireland. We visited each field six times, twice from
 0600-1100, twice from 1100-1600, and twice from 1600-2200. Visits began
 when oilseed rape reached Growth Stage 6 (flowering) and was conducted in
 the best weather possible (i.e., dry, clear skies, still, warm) to
 replicate the recommended conditions for pesticide application which
 coincide with optimal conditions for pollinator abundance. All
 observations took place from 15 June to 07 July 2021.
 On
 each visit, we walked three 15-minute transects (with 20 minutes in
 between) in two-hour blocks. Transects were walked at a slow, steady pace
 along field tramlines. Tramlines nearest the sides of the fields were
 designated ‘edge’ and the tramlines past 20 meters into the fields were
 designated ‘centre;’ composition of a pollinator assemblage can differ
 between the ‘centre’ and ‘edge’ of fields; an even number of transects in
 both locations were walked to get a representative measure of the area.
 Every insect pollinator visiting an oilseed rape flower within a one-meter
 radius of the observer was recorded. To establish the effect of time on
 pollen gathering, bees with visible pollen loads were distinguished from
 those without. For modelling purposes, we grouped insects into four main
 groups - honeybees, bumblebees, solitary bees, and hoverflies - as this
 represents the main functional groups of pollinators in the study region
 and is best suited to the resolution of our data.
 <em>Data collection and
 processing for nest data</em>
 To compare the effect of time
 on pollinators in oilseed rape crops with activity at the nest, we also
 recorded honeybee (<em>Apis mellifera</em>) and bumblebee
 (<em>Bombus terrestris</em> audax) activity at their nest
 entrances. Nest arrivals were used as the measure of activity since the
 number of arrivals is representative of the number of foraging trips.
 Activity of these two bee species was recorded at the UCD Rosemount
 Environmental Research Station from 01 to 31 July, for 24 hours a day in
 all weather conditions. <em>A. mellifera </em>and
 <em>B. terrestris </em>were tagged with Radio Frequency
 Identification (RFID) tags (mic3–TAG 64-bit RO, BeeID system; Microsensys
 GmbH, Erfurt, Germany); we used queen marking cages to stick tags to their
 thorax with Uhu Endfest Plus Adhesive (UHU GmbH & Co. KG,
 Bühl/Baden, Germany). Bee activity was recorded 24 hours a day except when
 RFID console data were downloaded. 
 Three <em>A. mellifera
 </em>hives were provided by Rosemount beekeepers. <em>A.
 mellifera </em>returning to the hive entrance were captured and
 tagged. We only captured those bees observed returning with a visible
 pollen load on their corbiculae to ensure they were foragers. Tagging of
 <em>A. mellifera </em>continued throughout the study duration
 with 199 <em>A. mellifera </em>tags being read in
 total. Three research <em> </em>colonies of
 <em>B. terrestris </em>were obtained from Biobest Group NV
 (Westerlo, BE) via Agralan Ltd. (Wiltshire, UK) with each colony
 containing a queen and approximately 50 workers upon delivery. Before
 outdoor placement, every worker from each <em>B. terrestris
 </em>colony was tagged. Afterwards, colonies were placed outdoors
 and allowed to forage freely. On subsequent days, workers observed
 returning to the colonies without a tag were captured and tagged, and 182
 <em>B. terrestris </em>tags were read in
 total.  Data from every day of the experiment,
 regardless of weather conditions, were included to capture an overall
 pattern of activity for both species. Legitimate foraging trips were
 specified by setting a threshold of at least 5 minutes between arrivals of
 the same tag. A 5-minute threshold has been used as the minimum for a
 ‘foraging bout’ length in honeybees, as orientation flight length rarely
 exceeds 5 minutes; a 5-minute flight has been used for <em>B.
 terrestris </em>as it is estimated to accurately represent a
 foraging bout. The number of arrivals was then aggregated into 15-minute
 intervals. Any intervals during which bees were tagged were removed, as
 the colonies were disturbed. Although 600 <em>A. mellifera
 </em>were tagged across all three colonies (approximately 200 per
 colony), due to misreads by the RFID system some tags were not detected,
 or detection frequency was inconsistent. Only 199 honeybee tags were read
 across all colonies which resulted in low readings of activity overall.
 However, data reflected patterns observed in the field and are thus
 assumed to be a representative subset. 
 We supplemented these data by
 also recording solitary bee (<em>Osmia bicornis</em>) nest
 activity from 29 to 31 July 2021. As an RFID system was not available to
 record solitary bee nest entrances, we used video cameras to record their
 activity from 0600 to 2200 on warm and sunny days which reflected the same
 timespan observed in the oilseed rape study.
 <em>O.
 bicornis</em> activity was recorded in two flight cages in the UCD
 Rosemount Experimental Research Station from 29 to 31 July 2021 (average
 sunrise at 0546 and sunset at 2128). <em>O.
 bicornis </em>females emerged from commercially available cocoons
 were marked and placed in each cage following mating and had access to
 flowering potted <em>Phacelia tanacetifolia</em> for forage as
 well as mud and water for nest cavity construction. Bees were placed in
 the cages five weeks before observations as they were used as the control
 group in a prior experiment. Video was recorded of nest activity in both
 cages from 0600 to 2200h for three days, apart from times when the cameras
 were switched out. Seven bees, five in one cage and two in another, were
 recorded. Since the bees could enter multiple nest cavities before
 locating their own, a threshold of 30 seconds between nest arrivals was
 used to ensure the time spent away from the nest was more likely for
 foraging than return orientation.
 <em>Weather
 recording</em> For all experiments, we recorded temperature,
 relative humidity, solar radiation, precipitation, and wind speed at
 30-second intervals throughout each observation day using a HOBO Micro
 Station Logger from the Onset Computer Corporation. In the field, we
 placed the logger at the edge of the oilseed rape field, while when
 recording <em>A. mellifera</em> and <em>B.
 terrestris</em> nest entrance activity, we situated the logger
 between the two sets of colonies. When observing <em>O. bicornis
 </em>we placed the logger outside the flight cages. Note that we
 only had one weather station; weather data recorded was only able to be
 recorded at one site at a time.
description: # Exploring relationships between time of day and pollinator activity in
 the context of pesticide use - data ## (1) Oilseed rape abundance and
 weather data transect - refers to the transect number site - the field
 number location - where in the field observations were made (center or
 edge) bumblebee - # of bumblebees observed without pollen load butterfly -
 # of butterflies observed honeybee - # of honeybees observed without
 pollen load solitary - # of solitary bees observed without pollen load
 bumblebee_pollen - # of bumblebees observed with pollen load
 honeybee_pollen - # of honeybees observed with pollen load solitary_pollen
 - # of solitary bees observed with pollen load datetimestart - the date
 (dd-mm-yy) and time (hh:mm) format an observation began datetimeend - the
 date (dd-mm-yy) and time (hh:mm) format an observation ended meantemp -
 the average temperature (°C) recorded by the weather station during the
 observation period meanrh - the average relative humidity (%) recorded by
 the weather station during the observation period meansolar - the average
 solar radiation (W/m^2) recorded by the weather station during the
 observation period meanrain - the average precipitation (mm) recorded by
 the weather station during the observation period meanwindspd - the
 average wind speed (m/s) recorded by the weather station during the
 observation period secssincemidnight - the time of day in seconds since
 midnight format * NA data for values in the rain column indicates that
 weather data was not available at these times ## (2 & 3) Bumblebee
 & Honeybee RFID data timestamp - date (dd-mm-yy) and time (hh:mm:ss)
 at which a bee with an RFID tag was first recorded passing through an
 antenna uid - the tag identification number unique to each bee collection
 - the colony to which each bee belonged firsttimefound - the first time a
 tag was detected passing through an antenna lasttimefound - the last
 instance at which a tag was detected passing through an antenna numfound -
 the number of times an antenna was detected passing through an antenna
 ant1 - an 'x' indicates the tag was sensed by this antenna, a
 blank cell indicates it was not sensed ant2 - an 'x' indicates
 the tag was sensed by this antenna, a blank cell indicates it was not
 sensed direction - the direction a bee was recorded going (departing,
 arriving, or unknown) depending on the order in which ant1 and ant2 were
 triggered ## (4) RFID weather data This dataset contains the weather
 variables recorded during the capture of datasets 2 & 3. datetime -
 the date (mm-dd-yy) and time (hh:mm:ss) a weather recording was made temp
 - temperature (°C) rh - relative humidity (%) solar - solar radiation
 (W/m^2) rain - precipitation (mm) windspd - wind speed (m/s)
 secssincemidnight - the time of day in seconds since midnight format * NA
 data for for two values in the rain column indicates that weather data was
 not available at these times ## (5) Solitary bee activity data obs -
 observation number (note observations were divided into fifteen minute
 intervals) datetimestart - the date (dd-mm-yy) and time (hh:mm) format an
 observation began datetimeend - the date (dd-mm-yy) and time (hh:mm)
 format an observation ended bee - the identifying color (or lack of color)
 for each solitary bee recorded cage - the cage in which the bee was
 recorded. only two cages (labeled five and three) were used in this study
 arriving - how many times that bee arrived to its nest during an
 observation ## (6) - Solitary bee weather data This is the weather data
 recorded during observations of solitary bees (data set 5) datetime - the
 date (mm-dd-yy) and time (hh:mm:ss) a weather recording was made temp -
 temperature (°C) rh - relative humidity (%) solar - solar radiation
 (W/m^2) rain - precipitation (mm) windspd - wind speed (m/s)