Nectar Dynamics and Pollinators Preference in Sunflower

SIMPLE SUMMARY: The survival of pollinators is in real danger, and the reasons are due to climate change, inadequate pesticide use, invasive species and diseases. The nectar produced by plants is the basic food for many of these insects, together with pollen. However, the scarcity of nectar secretion in certain plant species is becoming alarming, especially in recent years. We focused our study on sunflower species, a plant which is an object of debate within the scientific community for the strong industrial interest, but also for the decline in pollen, nectar and honey production displayed globally in recent decades. We tested a commercial hybrid variety in different soil conditions and verified nectar secretion and quality. We also evaluated the pollinator visiting habits using the same hybrid in comparison with a non-hybrid variety. Our findings point out the effect of compost with respect to nectar composition and the pollinators preference toward the non-hybrid variety. ABSTRACT: Nectar is a complex biochemical substance secreted with particular rhythm by flower nectaries. Nectar is the base of a mutualism in which pollinators consume nectar, as food source, and are involuntarily responsible for the transport of pollen and pollination. The dynamics and temporal patterns of nectar secretion are still not fully understood as well as the environmental and climatic factors influencing its production. The quantity and quality of nectar found in standing crops at flowering influence the mutualistic relationship with pollinators and their foraging behavior. This situation is even more significant considering the reduction in undisturbed environments, the loss of soil quality, the spread of monoculture agricultural management and the use of self-fertile hybrids. The objects of the study are understanding the relationship among soil properties and nectar quality, comparing the nectar composition in a sunflower hybrid variety and evaluate pollinator preferences in selecting nectar sources among hybrid and non-hybrid varieties. For these purposes, two different experimental tests were established. Results highlighted that fertilization strategy influenced crop biomass development, determined soil characteristics and nectar composition in Sunflower. However, when comparing nectar composition of hybrid and non-hybrid varieties of sunflower, no significant differences were found. Despite this, the analysis of number of visits on the two treatments showed statistically significant differences. This research provides further understanding of the very complex relationship among soil, crop and nectar to support the definition of agricultural management strategies and reach the optimal nectar composition level for pollinators in agricultural crops.