by Jarrad R. Prasifka, Beth Ferguson, and Karen K. Fugate
The nectar reward a sunflower provides to bees depends on the type or ‘variety’ and the conditions, especially temperature, in which the crop grows. To better understand how pollinators choose which sunflowers to visit, several sunflower varieties were grown under different temperatures and nectar collected from the flowers. Separate experiments also looked at how mesh bags (used to keep bees from moving pollen in breeding or insect research) change the nectar rewards available to bees. In general, much more nectar was found when plants were grown in warmer temperatures, but not all varieties showed the same pattern. The different temperatures in which plants were grown caused only small changes in nectar concentration or the types of sugars found in nectar. Sunflower plants covered with mesh bags contained much more nectar, and far more bees visited these plants when bags were removed. Even though not all varieties react to temperature changes in the same way, plant breeders can still create sunflowers that provide more nectar to bees. Because of how mesh bags change nectar rewards, research on sunflower pollination should avoid using these bags when possible.