Field trials to enhance kiwifruit production using Osmia bicornis and supplementary flowering plants

Kiwifruit has a strong dependence on insect pollinators, and yet the relatively low attractiveness of kiwi flowers to European pollinators may lead to deficits in production. In Italy, due to the scarce efficacy of the honey bee in pollinating kiwifruit, the most used strategy to mitigate this issue is artificial pollination with mass-produced pollen, which incurs high costs and increases the risk of disease; alternative strategies are thus direly needed. The aims of this study are i) to quantify pollination deficit and pollinator contribution to kiwifruit production and quality, and ii) to investigate the release of red mason bees Osmia bicornis (L.) (synonym Osmia rufa) (Hymenoptera Megachilidae) and the use of flower strips (supporting both wild pollinators and the released red mason bees) as strategies for the improvement of kiwifruit pollination. Through manipulative experiments in 3 golden kiwifruit orchards in Northern Italy, we verified that kiwifruit production in the area was significantly improved by insect pollinators, but also suffered from pollination deficit, with average reductions of 9% in fruitlet set, 15% in final fruit set, and 30% in seed number. Our findings confirmed successful population establishment of managed O. bicornis in most sites, and analyses of pollen collected in their provisions indicated that these bees effectively gathered kiwi pollen. While the presence of O. bicornis had limited but statistically significant positive effects on fruit production and quality, the introduction of flower strips had a distraction effect on O. bicornis and other pollinators, leading to some negative consequences on the target crop. This suggests a need for careful management of floral resources to balance the benefits of supporting pollinator populations with the goal of maximizing kiwifruit production; at the same time, the introduction of managed pollinators such as O. bicornis might be especially beneficial to this crop in agroecosystems that are poor in alternative flower resources.