Sweet Nectar

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Plants produce some serious chemical cocktails. Any compound that a plant produces that isn't involved in growth or reproduction is coined a secondary metabolite. These compounds often function as herbivore deterrents. We humans are well aware of this fact and have been utilizing plants as medicine for millennia. Though the human animal may appear unique in this aspect, self-medicating has nonetheless been discovered in many other animals. Everything from monkeys to birds and even elephants seek out specific plants for things like parasite control and birthing. A recent study published this month suggests that using plants as medication may even extend to insects. 

It has been documented that for a multitude of plant lineages, secondary metabolites are not restricted to vegetative structures. Many species produce secondary metabolites in their nectar. One interesting example of this can be found in coffee trees (Coffea sp.). These plants produce caffeinated nectar that has shown to keep bees coming back for more, not unlike we humans frequent our coffee pots. Plenty of other plants are doing this as well. Everything from amino acids, alkaloids, phenolics, glycosides and terpenoids have turned up in the nectar of different plant species.

Researchers wanted to know if these chemicals may be benefitting pollinators. By isolating the different compounds, researchers found that bumblebees drinking from these flowers had drastically reduced parasite loads, specifically the gut parasite Crithidia. About half of the compounds tested were implicated in reducing parasite load but one group in particular stood out, the tobacco alkaloids. 

Alkaloids such anabasine are not limited to tobacco plants. They can be found in the nectar of trees like the basswoods (Tilia sp.) and forbs like the turtle heads (Chelone sp.). Bees that drank nectar containing these alkaloids saw parasite reductions of upwards of 80%. However, like any viable medicine, there were side effects. The eggs of bees that drank these compounds took considerably longer to develop and hatch. This cost may be well worth the lower parasite transmission rates and likely do not pose considerable selective pressures.

Whether or not bees are specifically targeting these plants for their anti-parasite properties remains to be seen. More recent work has found that we must be tentative in our conclusions at this point. Tests on other nectar compounds have shown no benefit to pollinators. Either way, these findings have opened up a whole new door into the interactions between plants and their pollinators. 

Further Reading:

http://rspb.royalsocietypublishing.org/content/282/1803/20142471

http://f1000research.com/articles/4-73/v1