Carla Roybal, 2010

Prescott College

The dark side of sunflowers: What limits the pollinators of Helianthus annuus?

Helianthus annuus, (the common sunflower) appears to be an important resource for pollinators. It produces abundant and easily accessible pollen and nectar and hosts nearly 400 different species of pollinators. However, literature suggests that the pollen of Helianthus may actually be a poor dietary resource for many pollinators. Some potential shortcomings include a relatively moderate amount of protein within the grain, a possible coating of toxic alkaloids on the exterior of the grain, and a relatively impermeable pollen wall, rendering the interior nutritional content inaccessible. This study explored larval bee development on diets of sugar water plus Helianthus pollen amended to test two of these factors: low amino acid content and low extraction efficiency from entire pollen grains. Experimental treatments comprised unaltered Helianthus pollen, Helianthus pollen amended with the essential amino acids phenyalanine and arginine, Helianthus pollen ground with a mortar and pestle, and a combination of grinding and amino acid addition. The bee used for this study was the alfalfa leaf cutting bee, Megachile rotundata, a legume specialist not known to visit Helianthus annuus. The control provisions comprised the bee's own natural provisions (mainly Fabaceae and Lamiaceae) that were subsequently homogenized like experimental hand-made Helianthus provisions. Bee larvae performed very poorly in all Helianthus treatments, suggesting that there is at least one additional trait of Helianthus pollen responsible for the high rates of mortality within the study group.

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