Primary and secondary exposure to pesticides is known to cause sublethal effects which can be harmful to insect pollinators and the ecosystem services they provide. Pesticide application guidelines that take pollinators into account are typically shaped around the behavior of the honeybee (Apis mellifera) and exclude unmanaged pollinators whose behavior is known to be different. As there is an overlap in the ideal conditions for pollinator activity and pesticide application in agricultural systems, we wanted to know if there is an ideal time of day to apply pesticides to minimize direct insect exposure. We aimed to evaluate how differentially active various pollinator groups are across periods of day to explore their potential contact with applied pesticides. We walked transects from 0600 to 2200h at three Oilseed Rape (Brassica napus L.) fields in Ireland to capture the abundance of managed and unmanaged flower visitors across daylight hours. We also recorded three bee species at their colonies across time of day to compare with the field observations.
Results/Conclusions
We found that in the field, taxa and time of day are strong determinants of pollinator abundance and that relationships between pollen collecting behavior and time of day differed between bee 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 in the field. These results suggest that even if pollinators aren’t observed on the target crop they could still be active in field margins. Overall, honeybee and solitary bee abundance and activity was found to peak in the middle of the day, while bumblebee (Bombus spp.) abundance and activity was consistent throughout daylight hours. Hoverflies were relatively abundant in the morning and increased in number towards the late afternoon and early evening. Based on our findings we strongly recommend not applying pesticides in the middle of the day; whether guidelines are formed to spray in the morning or evening hours should account for the diversity of behaviors among pollinating insect groups to time in order to reduce pollinator exposure to pesticide.
