Dangerous flowers and pollinators

An interesting article has been published in New Scientist (April 25 - May 1, 2015) under the title 'Bitter sweet nectar: Why some flowers poison bees'.

The article describes how in 401 BC a total of 10,000 Greek warriors were behaving as madman on the way back to home after a war against the king of Persia after having eaten some honey made by local bees. They were lucky as they recovered and could continue going home. However, during later wars, there were armies that were slaughtered by the enemy because the soldiers were unable to fight after having eaten the honey; some local armies even used the honey to intoxicate the soldiers of foreign armies and thus this became one of the first known chemical weapons used during war.

Chemicals released in nectar of plants

The article describes how some plants leak certain chemicals such as nicotine and caffeine into their flowers and so in their nectar. In general, insects don't like these substances as they taste bitter and not sweet. But in the case of caffeine, at very low doses, it probably has a nice effect on the brain (as in humans) and makes the honey a little addictive to the insects. As a result, pollinators prefer plants that produce some of these chemicals and will return more often to the flowers of these plants than to flowers of other plants, therefore these chemicals probably increase the plants reproductive success.

The bitter-tasting nicotine seems to repel both pollinating insects and birds, but together with a strong attractive scent molecule (benzylacetone), both pollinating insects and birds are attracted to the flowers. However, as soon as they taste the nectar of these plants, they go away, taking only a little nectar with them while more is left in the flower. Doing so, over a longer period the flowers have nectar that insects and birds that are attracted to the smell of the flowers will spread and thus the likelihood that the nectar reaches more plants increases, and thus also the reproductive success.

Rhododendron - beautiful but it seems also dangerous

To return to the start of the article, it seems the common rhododendron (Rhododendron ponticum) is responsible for producing the 'mad honey' and even certain pollinators are intoxicated by its nectar such as honeybees who die within hours after having palpitations (= abnormality of the heartbeat) and becoming paralysed (paralysis = loss of muscle function) as the flowers produces nectar that contains the neurotoxins grayanotoxins that are responsible for keeping sodium channels open in all nerve and muscle cells. However, bumblebees don't mind these toxins and thus in areas with many rhododendrons, few honeybees can be found while bumblebees are thriving. Very interesting.

Bumblebee - also looking for nectar to produce honey

Nectar as medicine for insects

Then the article starts to discuss how insects can use nectar as medicines because some (many? all?) nectar have antibiotic and/or antiparasitic properties and can save large numbers of pollinators by killing bacteria and/or parasites that would otherwise destroy large parts of bee colonies.

But then the article mentions that, as the list of plant species with toxic nectar grows, certain ecologists wonder whether this could be a contributing factor to the global decline in pollinators. And thus, of course it is not the fault of humans and the chemicals they produce (such as pesticides but also toxic fossil fuels) that is the reason of the decline in pollinators but plants. However, these scientists seem to forget that these bees and plants are relying upon each other for millions of years and as described in the previous paragraph, even seem to keep colonies of pollinators healthy by destroying their enemies and thus contributing to healthy colonies.

Indeed, if there are only rhododendrons in an area so honeybees can only use this nectar, honeybees will disappear from that area unless some may not feel its toxic effects such as the bees that produce the 'mad honey' (I think this may be due to a mutation in the sodium channels although maybe other mechanisms are involved - more research is needed to solve this mystery but may even benefit humans when the knowledge allows us to understand why for instance certain people have a certain illness or respond differently to certain drugs than other people and thus money into this area isn't wasted money). But, if there are many plants around, then, as the article states, the pollinators are clever enough to avoid the harmful plants and only visit the flowers of plants that are beneficial to them (and thus even insects can learn in order to survive the dangers of nature while benefit from its gifts). Therefore, as the article concludes, there should be a large enough variety of plants with all sorts of flowers that produce different types of nectar so a diversity of bees and other pollinators can co-exist and pollinate a large number of plants. This will also result in the production of a large number of different types of honey. Nothing new, already many years it is known that diversity in nature is important.

Mono-culture one reason for collapse of honeybee colonies?

I think not only the use of pesticides and pollutants may be a reason why the numbers of pollinators are going down, but this may also be due to the fact that pollinators are having access to an increasing limited number of beneficial plants. Indeed, to maximise yields, honeybee houses are placed in areas where for instance only apple trees of few species are cultured. Bees can survive on the nectar and maybe the nectar even contains certain 'medicine-like' properties such as antiparasitic or antifungal actions (I don't know whether this is already known). But, as we should know, use always the same drug against an invasive species and it is likely the invasive species develops tolerance against the drug. Or the nectar of apple trees doesn't have these 'medicine-like' actions and thus, as the bees are housed in a mono-culture, they can't find and thus yield nectar that have these 'medicine-like' actions. So, while bees can feed on the nectar of the apple trees, by having access to only a very few types of nectar, it may be possible that certain diseases (such as mites, viruses, parasites, fungi) can affect the colonies as no nectar is present with actions against these diseases (at this moment, many honeybee colonies suffer, known as Colony Collapse Disorder (CCD)). And thus, maybe not only pesticides are causing havoc amongst bee colonies but maybe also the absence of the large number of different type of plant species, each having their own type of antibiotic/antiparasitic actions. Maybe we should only increase biodiversity again to see an increase in the numbers of honeybees and other pollinators while we should prevent to introduce only a small number of plant species that we think are positive as others may be even more beneficial but we don't know yet or too many of the plants with 'medicine-like' actions may kill the insects. And an increased biodiversity with many plants producing their own defences against invasive species may allow a reduction in the use of pesticides.