Is Honey Good for Bees?

Not all flowers give up their nectar graciously. Some of them include doses of poisons. Nicotine and caffeine, for example, are both insecticides, but can be found in the nectar of some plants. Thymol is another example. Most are not very toxic to bees, on the whole, but they do have toxic effects and, in high doses, can be lethal.

At first glance, it’s difficult to see why an insect-pollinated plant would put an insecticide in the nectar, but it seems that bees and other pollinators are attracted to nectar with small doses of nicotine or caffeine in them [1,2]. However, although they make more visits, they help themselves to less nectar than usual [3]. If a plant can increase the number of pollinator visits, without having to pay the full price in nectar, why wouldn’t it? Expecially if the toxins also deter ‘nectar thieves’, such as ants, which just take the nectar but do no pollination.

From the plant’s point of view, that’s great news. It’s not such good news for the pollinators, though, who have to deal with the toxin. Happily, pollinators have mechanisms for dealing with toxins.

Honeybees deal with toxins, at least in part, by breaking them down using a bunch of proteins called P450s. They’re naturally in the bees, but they increase production in the presence of certain chemicals found in pollen, propolis or honey. The one that seems to have the greatest effect is one called p-coumaric acid, which is mostly found in pollen [4], though some things in propolis have a similar effect.

This is neat, because is looks like the plants are making good for their toxic trickery by helping pollnators cope with the poisons while nectar-thieves, the naughty insects that take the nectar and don’t bother with the pollen, don’t get the benefit.

The toxins in nectar (and honey) aren’t the only toxins in the hive. Fungi also live in the hive, and some of them produce toxins of their own [5] which bees are able to fight off better if their food has propolis in it. Other toxins, introduced by beekeepers, also exist. As well as thymol (in Apiguard, for example), there’s tau-fluvalinate (the active ingredient in Apistan) and flumethrin (ditto for Bayvarol), which are used to kill varroa mites. Strangely, although these pyrethroids are toxic to insects in general, honeybees seem able to tolerate them at relatively high doses, thanks to their specific bunch of P450s [6,7].

This is all very interesting, and highlights the complexity, and importance, of just one of the many immune-system and detoxification mechanisms that living things rely on. But what can we do, if anything, with this information? Should we take care to leave propolis in the hive? Should we make sure the bees are fed honey after varroa treatment? Should we feed pollen along with the candy in winter, or would that risk encouraging the bees to make more brood than is wise for the weather?

I don’t know, but it’s food for thought.

1. Singaravelan N, Nee’man G, Inbar M, Izhaki I (2005), Feeding Responses of Free-flying Honeybees to Secondary Compounds Mimicking Floral Nectars. Journal of Chemical Ecology 31: 2791-2804
doi: 10.1007/s10886-005-8394-z
2. G. A. Wright, D. D. Baker et al. (2013) Caffeine in Floral Nectar Enhances a Pollinator’s Memory of Reward Science Vol. 339 no. 6124 pp. 1202-1204
doi: 10.1126/science.1228806
3. Kessler, D. and Baldwin, I. T. (2007), Making sense of nectar scents: the effects of nectar secondary metabolites on floral visitors of Nicotiana attenuata. The Plant Journal, 49: 840–854.
doi: 10.1111/j.1365-313X.2006.02995.x
4. Mao W, Schuler MA, Berenbaum MR (2013) Honey constituents up-regulate detoxification and immunity genes in the western honey bee Apis mellifera PNAS 110: 8842-8846
doi: 10.1073/pnas.1303884110
5. Niu G, Johnson RM, Berenbaum MR (2011) Toxicity of mycotoxins to honeybees and its amelioration by propolis. Apidologie 42:79–87
doi: 10.1051/apido/2010039
6. Mao W, Schuler MA, Berenbaum MR (2011) CYP9Q-mediated detoxification of acaricides in the honey bee (Apis mellifera) PNAS 108: 12657-12662
doi: 10.1073/pnas.1109535108
7. Johnson RM, Wen Z, Schuler MA, and Berenbaum MR (2006) Mediation of Pyrethroid Insecticide Toxicity to Honey Bees (Hymenoptera: Apidae) by Cytochrome P450 Monooxygenases. Journal of Economic Entomology 99(4):1046-1050
doi: 10.1603/0022-0493-99.4.1046