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ARS Home » Pacific West Area » Tucson, Arizona » Honey Bee Research » Research » Publications at this Location » Publication #214086

Title: Do Honey Bees Increase Sunflower See Yields?

Author
item Degrandi-hoffman, Gloria

Submitted to: American Bee Journal
Publication Type: Trade Journal
Publication Acceptance Date: 1/1/2008
Publication Date: 1/1/2008
Citation: Hoffman, G.D. 2008. Do honey bees increase sunflower seed yields?. American Bee Journal. (148):155-156.

Interpretive Summary: Some commercial sunflower varieties can self-pollinate as florets mature and set seed. Whether seed set can be improved by honey bee pollination is not clear. We compared seed set on sunflowers with and without exposure to bees. Ten sunflower varieties were evaluated. We also examined the role of temperature and relative humidity on seed set. In the first planting, the number of foraging honey bees was smaller than in the second and seed set for most cultivars did not differ between those with and without foraging bees. In the second planting though, a majority of cultivars had significantly greater seed set when flowers were exposed to bees compared with when they were not. The weight of seeds from open-pollinated plants was greater than from those where bees were excluded. Environmental conditions played a role in seed set. In the first planting, average maximum and minimum temperatures were significantly higher than in the second, and seed set was significantly lower on plants where bees were excluded. Under the high temperature conditions though, some cultivars set four times more seed on open-pollinated flower heads compared with those where bees were excluded. These results suggest that foraging activity and cross-pollination by bees might mitigate reductions in seed set caused by high temperatures. The study also showed that bee pollination can improve seed yields in self-pollinating varieties if populations of bees are sufficiently large.

Technical Abstract: Ten self-fertile commercial sunflowers cultivars were evaluated for seed set with and without exposure to bees. In the first planting, the number of foraging honey bees was smaller than in the second, and seed set for most cultivars did not differ between those excluding bees and ones that were open-pollinated. In the second planting though, a majority of cultivars had significantly greater seed set when capitula were exposed to bees compared with when they were not. The weight of seeds from open-pollinated capitula was greater than from those where bees were excluded. Environmental conditions also played a role in seed set. In the first planting, average maximum and minimum temperatures were significantly higher than in the second, and seed set was significantly lower in capitula where bees were excluded. Under the high temperature conditons though, some cultivars set four times more seed on open-pollinated capitula compared with those that were bagged. These results suggest that foraging activity and cross-pollination by bees might mitigate reductions in seed set caused by high temperatures.