Dear Mohamed,

Your last question is part of the answer : in some cases this can be explained by the fact that the toxic compounds are located in the sap or other tissues of the plant, but not in the nectar (or in smaller amounts).This allows the plant to be protected against herbivorous while not harming pollinators.

Another explanation is that some molecules poisonous to mammals could not be toxic for insects : the cardiac glycosides in Calotropis might have no effect on bees for example (see http://en.wikipedia.org/wiki/Cardiac_glycoside), but I don't know if this was the object of detailed studies.

Finally but I have no information about this, it might be possible that some bees are protected from this toxic compounds. Very interesting subject anyways, let us know if you find some more info.

Thanks Vincent for nice clarification indeed, it is very interesting subject. I was thinking that may be the bees gut have some metablosim change the structure of the nectar. I think the best option is to do analysis for the plant nectar and pollen. Do you know that Xylocopa used the stem of the toxic plant to build their nest. Very interesting.

Calotropis pollination is very elaborate and fantastic - pollen grains are present in specilised structures called pollinia which bees carry from one flower to another. I suppose, if nectar contained toxic compounds - insects/ bees would avoid that plant/ flower- which should not be the case of insect pollinated plants - most toxic allelochemicals would repel insects and bees. There are some reports of nectar toxicity however-

http://www.ibra.org.uk/articles/Toxicity-of-nectar-of-tea-Camellia-thea-L-to-honeybees

http://en.wikipedia.org/wiki/Bees_and_toxic_chemicals

There is a nice recent paper talking about that alcaloids help bumblebees to deal with gut parasites. You find the information here and some comments on my blog.

http://www.bee-safe.eu/alcaloids-nectar-agains-bumblebee-parasites/

http://www.bee-safe.eu/article/dose-makes-poison-paracelsus/

Datura inoxia is visited by honeybees for its nectar

Thanks very much for our interesting ANSWERS.

All the best

Mohamed

Great query, however this begs the question: How can these Calotropis plants live with the sodium-potassium pump inhibitor calotropin? Needless to say that all living things use sodium-potassium. Symbiosis with microbiota? The pant as network? I am going to extrapolate from generalities: Toxins seem to always a role in symbiosis, The photosynthesizing bacteria that coexist with coral often produce Tetrodotoxin. These Tetrodotoxin producing bacteria, Pseudomonas and others go right up the food chain, living with xanth crabs, puffer fish, and the blue spotted octopus in increasing toxicity. You see they produce a long term neurotoxin coupled with a short term antitoxin, as long as you let them live with you, you will have access to the antidote. It is quite probable that ecosystem that comprises Calotropis includes symbiotic microbes that prefer to live in a calotropin rich environment and provide the antidote for free while perhaps helping to produce thesodium-potassium pump inhibitor . Something similarly protective is possible for the bees. maybe the source is the microbiome of the Calotropis itself. Nota Bene plants and their microbial networks is new and may not be the case for Calotropis.

Plants hosting toxic bacteria was once a "batty idea" when Oliver Sack and Paul Cox suggested that cycads lived in symbiosis with cyanobacteria which then produced the neurotoxin beta-methylamino-L-alanine (BMAA) found in especially in the cycad seeds. These seeds were eaten by flying bats which biomagnified the poison, then humans ate these bats in Guam and suffered symptoms like Alzheimers, Parkinson's and ASL This poison antidote circle extends even to viruses and their prey; from Nick Lanes article in Nature: viral genes in the cell encode a long-lived toxin as well as its short-lived antidote; cells that stop expressing the viral genes run out of antidote and die. From https://www.nature.com/news/2008/080528/full/453583a.html

I hope this peaked your curiosity Mohamed.

Thanks a lot for this great clarification, although I left Saudi Arabia 3 years ago and the questions was to figure out how larger carpenter bees is adapted to get nectar from Calotropis procera. The stems of the plans also were used by bees for nesting. I may try to find this work again when I will be back to Egypt after my research visit to Hungary.

Thanks again Christopher and I wish for you all the best.