Benefits of Insect Pollination to Confection Sunflowers Differ Across Plant Genotypes

Sunflower (Helianthus annuus L.) is a major global crop that shows variable dependence on insect pollinators across systems (e.g., hybrid seed production, oilseed, and confection systems), growing regions, and plant genotypes. Although modern sunflowers have been bred for increased self-fertility, selfing rates still vary across genotypes, resulting in differing pollinator dependence. Furthermore, some plant genotypes may attract a greater abundance or diversity of pollinators, thereby receiving greater pollinator benefits. The goal of this study was to evaluate the benefits of insect pollination to different modern confection sunflower varieties. We conducted pollinator exclusion experiments for 15 confection hybrid varieties in 2014 and 2015 to measure self-fertility and pollinator-mediated yield increases. To assess whether pollinator benefits differ across hybrids due to their relative attractiveness to pollinators, we compared bee visitation rates among hybrids and related these rates to seed mass. Overall, sunflower seed mass was 26% higher on open flowers than on bagged ones. Furthermore, seed mass on open flowers increased significantly with pollinator visitation rates. Yield increases with insect pollination differed among hybrids, however, with 5 of 15 showing significant increases ranging from 39 to 108%. Pollinator visitation rates and degrees of self-fertility also differed across these hybrids, in part explaining the variability in pollinator benefits that they received. Our study shows that insect pollinators increase confection sunflower yields, but benefits vary across hybrids due to their self-fertility and relative attractiveness to pollinators.