Wild bee associations with blueberry crops in Argentina, 2020-2021

Fieldwork instrumentation used: No fieldwork instrumentation was used outside of GPS to position the sites locations.

Methods of collection: Pollinators on nine farms were sampled, eight in 2020 and six in 2021—five of these farms were sampled in both years. Five farms had honeybee hives to enhance crop pollination while four rely on wild pollinators or feral honeybees. On each farm, an edge area (25 m from the field margin) and an inner area (50 m from the field margin) were established, each comprising two 70 m transects running parallel to the field margin (width 2m) and separated by 8 m. On each of the four transects 25 plants in full flower were selected on which three 25-second pollinator counts were conducted, one in the morning, one at midday and one in the afternoon. All sampling took place between 10:00 and 17:00 on sunny days with low wind and a temperature above 15°C. The abundance of honeybees, small wild bees (any bee smaller than a honeybee), hoverflies (Syrphidae) and butterflies were recorded. Hummingbirds and large wild bees (bumblebees Bombus spp. and carpenter bees Xylocopa spp., which are all larger than honeybees) showed behaviours that made them difficult to record as they fled when surveyors approached the plants. Therefore, after every 25-plant pollinator counts, the researchers walked the same transect to record the abundance of hummingbirds and large wild bees for 5 min. These were recorded within the confines of the transect, as well as those that were observed nearby but outside of the transect. This was assessed for the single blue-berry cultivar Emerald.

To compliment this data on pollinator abundance, the contribution of pollinators to fruit set for the blueberry crops was assessed. A field experiment was conducted to maximize variation in stigmatic pollen load. In one farm 20 plants of Snowchaser cultivar were randomly selected and two flowering branches for each plant were selected that were similar in orientation, size and number of flowers. On these branches, two treatments were applied: 1) pollination exclusion – this treatment consisted of a nylon mesh bag surrounding the flowers to prevent animal pollination; 2) free pollination – the flowers were exposed to natural pollination. The number of flowers and buds on branches was counted before bagging. When the fruits were fully mature, they were counted to assess fruit set. This assessment was undertaken on the cultivar Snowchaser.

How values were arrived at: Values of pollinator abundance determined from transect walks were based on visual observation and identification where possible in the field.

Nature and units of recorded variables: All data on abundance of pollinators represents counts of individuals. Data on fruit set represents counts of the number of fruits, buds and flowers.

Processing steps performed on the data: No data has been transformed.

Quality control/assessment applied to the data: All field workers were either experts with a long track record of pollinator identification or underwent extensive training. Questionable specimens were collected for subsequent identification under laboratory conditions. Data was collected in the field using pre-prepared data sheets. Data sheets were checked both visually and following data entry into digital format by confirming where outlier abundances (>2SD from mean) were found that these were consistent with raw field data sheets.

Limitations on the data’s reliability: Transect walks were not of a fixed width and so bumblebee abundance cannot be converted into a true measure of density.