Mason bees sometimes specialize in sunflower pollen to fend off parasites.
Bees evolve to specialize in different kinds of pollen for a variety of reasons. Some specializations arise from the availability of plants within a species’ range, while it turns out that some may develop as a response to parasitic activity. Sunflowers, which include dandelions, daisies, and thistles, generally produce pollen that is a poor quality food for bees. Those that feed exclusively on this kind of pollen are often underdeveloped, or grow more slowly than other bees, and sometimes don’t grow at all.
But there are still bees that specialize in sunflower pollen, and that specialization has evolved in multiple places around the world. Enter the sapyga wasp, a parasitic insect that lays its own eggs in the nests of solitary mason bees. The wasp larvae hatch and kill off the bee eggs while eating their honey provisions. But it turns out that honey made from sunflower pollen is no good for the wasps. In laboratory tests, researcher Dakota Spear found that wasps fed on sunflower provisions had a significantly lower survival rate than wasps fed on other honey provisions.
As a result, the sapyga wasps tend to avoid the nests of sunflower specialized bees, which works out well for the bees. The fact that sunflower pollen isn’t the best food source for them might be enough to balance out reducing the risk of losing entire nests to invasive wasps. Bees which develop slower than their peers are better than no bees at all.
This knowledge gives us a better understanding of bees more broadly, who seems quite capable of adapting to deal with new problems, like parasitic wasps, and still survive. Whether that adaptability is enough to help preserve bee populations around the world I the face of human activity is yet to be seen. But it also helps us understand why certain animals will evolve to focus on less valuable or efficient foods, like sunflower pollen.