> Plant toxin levels in nectar vary spatially across native and introduced populations

I think it's tempting to assume that toxic substances occur in nectar and pollen "for a reason," when they may in fact be there as a side effect of the plant's production of protective toxins in the leaves, for example. 

The amount of nicotine in nectar is much lower than that in the leaves of the tobacco plant, and may be an unavoidable consequence of the plant having evolved poisonous leaves as a defense against herbivores. 

I find it extremely interesting that some plants are able to produce very mild flavored nectar while having very pungent leaves (Salvia mellifera) and others produce very strong dark honey, despite no significant odor components in the stems and leaves (Fagopyrum esculentum). 

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> Nicotine is synthesized in the root and transported to all above-ground plant parts, including floral rewards, with nicotine concentrations in leaves and flowers being greater than that in nectar.  -- Irwin, R. E., Cook, D., Richardson, L. L., Manson, J. S., & Gardner, D. R. (2014). Secondary compounds in floral rewards of toxic rangeland plants: impacts on pollinators. Journal of Agricultural and Food Chemistry, 62(30), 7335-7344.

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> Determining where imidacloprid concentrates in the flower; the petals, the anthers (by extension pollen), or the nectar, is of most interest to the issue of pollinator exposure. This study shows that IMI, when applied as soil and trunk injections, translocates primarily to leaves and secondarily to flowers. 

> Further evidence to support low to no exposure risk is supported by the absence of IMI in nectar and forager samples and the absence of metabolites in pollen, nectar and forager samples. -- Johnson, J. D. (2012). The role of pesticides on honey bee health and hive maintenance with an emphasis on the neonicotinoid, imidacloprid.

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