Is pollinator visitation of Helianthus annuus (sunflower) influenced by cultivar or pesticide treatment?

Beneficial insects, such as Apis mellifera (honey bees) and Bombus sp. (bumble bees), play important roles in the environment as pollinators, and they are directly affected by agronomical practices, such as pesticide spraying or the selection of crop cultivar. Sunflower is an important resource for these pollinators, and its yield is highly dependent on pollination. Six sunflower hybrid cultivars (ES Biba, Gonzalo, Drake, Vellox, NK Neoma, and P63LE10) were used to compare the visitation rates (VR) of pollinators during flowering in three years (2015, 2016, and 2017). From this set, cultivar P63LE10 was selected to evaluate how pesticide treatments (mixture of two insecticide products containing acetamiprid and pirimicarb, respectively, and two fungicide products containing propiconazole plus prochloraz and dimoxystrobin plus boscalid, respectively) affect pollinator visitation. The amount of pesticide residue in sunflower inflorescences was analyzed to determine the content over the duration of the experiments. The sunflower cultivar P63LE10 was significantly the most attractive to both groups of pollinators in 2017. This cultivar was visited by the highest number of honey bees also in the other years. For bumble bees, cultivar P63LE10, along with cultivars NK Neoma and Vellox, had the highest visitation rates in 2015 and 2016. In 2017, plants treated by the fungicide dimoxystrobin plus boscalid had the highest visitation rates for both groups of pollinators. For bumble bees plants treated with this fungicide were significantly more visited (VR 23.1 ± 2.1%) than these treated with insecticide with pirimicarb (16.4 ± 2%) and the untreated control (17.9 ± 1.7%), and for honey bees plants treated with dimoxystrobin plus boscalid were significantly more visited (VR 24 ± 4.5%) than all other treatments except with acetamiprid (20.5 ± 3.5%). The residues of tested pesticides were found in blooms for the whole time of the experiment (range of values for 2016 and 2017 [ng/g]: acetamiprid 144-6, 3360-56; pirimicarb 177-12, 223-10; prochloraz 380-6, 1970-912; propiconazole 324-17, 1024-1018; boscalid 216-154, 9600-1319; dimoxystrobin 452-137, 6560-911). The influence of cultivar was more important than pesticide treatment in the selection of a preferred food source by pollinators.