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Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/19/2006 Publication Date: 8/20/2006 Citation: DeGrandi-Hoffman, G., Chambers, M. 2006. Effects of Honey Bee (Hymenoptera: Apidae) Foraging on Seed Set in Self-fertile Sunflowers (Helianthus annuus L.). Environ. Entomol. 35(4): 1103-1108. Interpretive Summary: Some commercial sunflower varieties can pollinate themselves as florets mature and set seed. Whether seed set can be improved on such self-pollinating varieties by introducing honey bees is not clear. We compared seed set between sunflowers exposed to bees with those that were bagged so that bees could not forage on the florets. Ten sunflower varieties were evaluated. We also examined the role of temperature and relative humidity on seed set and whether the effects could be mitigated by honey bee pollination. In the first planting when temperatures were significantly higher than in the second, the number of foraging honey bees was smaller than in the second, and seed set for most cultivars did not differ between flower heads that were bagged and ones where bees could forage. In the second planting though, a majority of cultivars had significantly greater seed set when florets were exposed to bees compared with when they were not. The weight of seeds from open-pollinated florets also 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 in flower heads 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 that were bagged. These results suggest that foraging activity and cross-pollination by bees might mitigate reductions in seed set caused by high temperatures. The study also shows that bee pollination can improve seed yields in self-pollinating varieties if populations of bees are sufficiently large. Technical Abstract: Ten self-fertile commercial sunflower 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, 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 conditions 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. |
